Glossary
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Want to brush up on your knowledge? Here are some commonly used industry terms. Of course, our TPG experts are always happy to chat, contact us today and let us help you on your next project.
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A
Absolute Zero
The lowest theoretical temperature. At absolute zero, a body would have no molecular motion of heat energy. Absolute zero is the zero point on the Rankine and Kelvin scale. (-273.15°C or-459.67°F)
Accuracy Calibration Accuracy
The potential error of a device compared to a physical constant or agency standard.
Activation
An automated or manual method of turning a radiant snow melting system, radiant floor heating system, radiant roof snow and ice melt system, or radiant heating system on and off.
Activation Device
A sensor, thermostat or any other device that is used to turn a heating/snow melting system on and off.
Address
For digital communication between host computer and control, is a numerical value, typically between 1 and 255. The same address must be entered into both the computer program and the specific control to be addressed, or communicated with.
Alarm
A control condition or function, indicating that the process is at a predetermined amount above and/or below the set point.
Alarm relay options
Normally energized (relay energized when not in alarm) normally de-energized (relay not energized unless in alarm). Latching means a reset button must be pushed when the temperature drops below the alarm setting plus dead band.
Alarm Type
Typical choices for PID controls are: disabled, high, low, + deviation, -deviation, +/- deviation., and event (for ramp soak units.)
Algorithm
A set of rules with a finite number of steps for solving a problem.
Alternating Current (AC)
An electrical power system where the voltage reverses, alternating negative and positive. Typical frequency is 50 or 60 Hz. (cycles per second)
Ambient Compensation
The ability of an instrument to compensate for changes in the ambient temperature so that the changes do not effect control accuracy.
Ambient Temperature
The temperature of the immediate surroundings in which equipment is to operate.
Ambient Temperature Sensor
The temperature of something surrounding something else, i.e. The ambient temperature of a room is the temperature of the air surrounding a mechanism to measure temperature.
Ampacity
The current (in amperes) that a wire can carry without exceeding its temperature rating.
Ampere (amp)
The rate of flow of current in a circuit.
Analog Indication
A meter with graduated scale and a pointer that moves to indicate process condition.
Analog Output
A voltage or current signal that is a continuous function of the measured parameter.
Analog Set Point
Potentiometer adjustment of the control setting
Anneal
To relieve stress in a metal or glass material by heating to just below its melting point, then gradually cooling to ambient temperature. Annealing lowers tensile strength while increasing flexibility. Tubular heaters are annealed prior to forming.
ANSI
American National Standards Institute
Anti-reset Windup
A feature in 3 mode (PID) controls which prevents the integral (automatic rest) circuit from functioning when the temperature is outside the proportional band.
Approved
Acceptable to the authority having jurisdiction (for enforcement of the National Electrical Code, for example).
ASME
American Society of Mechanical Engineers.
ASTM
American Society for Testing and Materials.
Atmospheric Pressure (Standard)
Pressure exerted by the earth’s atmosphere on the objects within. Measured at 60°F (15°C), at sea level, standard atmospheric pressure is 14.7 psia.
Auto-Trace
A historic trademark of the families of self-regulating heating cables manufactured by Pentair Industrial Heat Tracing Solutions (formerly the Chemelex Division of Raychem).
Autoignition temperature (AIT)
The AIT is the minimum temperature at which a material can spontaneously ignite without an external source of ignition. This is different from the flash point of a liquid, which is the lowest temperature at which the liquid gives off sufficient vapor to form an ignitable mixture with air near the surface of the liquid or within the vessel used. The flash point of gasoline is -50°F and the AIT is 536°F.
Automatic Reset (Integral)
The integral function of a control that automatically compensates for the difference between the set point and the actual process temperature. A signal moves the proportioning band up or down to correct for the droop or offset error.
Automatic Tuning (of control parameters)
A control that calculates the optimum PID parameters with a built-in software algorithm to eliminate manual tuning efforts.
Autotherming
An operating characteristic of self-regulating heating cables that results in a substantial change of its electrical resistance over a small temperature increment— the autotherming temperature is the temperature at which this change occurs.
Auxiliary Output
Additional outputs for control of functions other than the primary control output, such as lights, buzzers, horns or gas purges that are triggered by the control alarm function.
Auxiliary Setpoint
An alternate set point on some PID controls, which can be selected from a button or external signal.
AWG
American Wire Gauge.
AWG (American Wire Gauge)
Also known as B and S wire gauge. Standard system to specify the diameter of wires for both power and control circuits. The larger the gauge number, the smaller the wire diameter.
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B
Band and Nozzle Heaters
Component heaters designed to heat cylindrical objects such as plastic extruders. A variety of sizes and constructions are available.
Bandwidth
The total temperature variation measured at some point in the system, normally the process.
Baud Rate
In serial communications, the rate of information transfer in bits per second. Must be set for the same value in the controller and the host computer program. Typical values are 1200, 2400, 4800, 9600, and 19200. The control, computer and wiring must be able to operate at the baud rate selected.
Bend Radius (minimum)
The minimum radius for bending a wire, heating element or heat trace cable, without damage.
Blackbody
A theoretical object that radiates the maximum amount of energy at a given temperature and absorbs all energy incident upon it.
Boiling Point
The temperature at which a substance in the liquid state transforms to the gaseous state. Commonly refers to the boiling point of water (100°C or 212°F at sea level).
Braid
A flexible woven covering, usually of metal wire, covering an insulated wire to provide a ground path (or shield) or to protect from mechanical damage.
Branch-circuit
The electrical current path from an individual branch-circuit breaker (or fuse) to all connected heating cable circuits.
BTU
The British thermal unit (BTU or Btu) is a unit of energy used globally in the power, steam generation and heating and air conditioning industries. Although it is in common use in these industries, in scientific use it has been replaced by the SI unit of energy, the joule (J). In North America, the term “BTU” is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills, and air conditioners. When used as a unit of power, BTU per hour (BTU/h) is understood, though this is often confusingly abbreviated to just “BTU”. In the UK and other parts of the world it is written BTU. One Watt is equivalent to 3.41 BTU/hr.
Bulb & Capillary
Refers to thermostat construction which has a bulb filled with a fluid in the process. The increasing heat forces the fluid through a narrow tube into a bellows. The bellows actuates a snap switch, at a temperature determined by the knob setting which moves the switch toward or away from the bellows.
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C
C-UL
This is an acceptance of UL (Underwriter’s Laboratory) approval of a product. Often accepted by customers who would normally require CSA approval.
Cable Repair Kit
When RayChem Cable is damaged, a Cable Repair Kit is used to repair the damaged portion of the cable without replacing the entire length of cable.
Cable sets
A pre-terminated MI heating cable complete with a heated section and non-heated cold lead section.
Calibration
The process of adjusting an instrument so that the indication is accurate compared to the actual value.
Calorie
The amount of thermal energy required to raise one gram of water 1°C at 15°C
Cascade
Control function where the output of one control loop provides the set point for a second loop, which determines the control action.
CE
Marking to show compliance with all essential safety requirements of European Union directives.
CEC
Canadian Electrical Code.
Celsius
(Centigrade) a temperature scale with 0°C defined as the ice point and 100°C as the boiling point of water at sea level.
Ceramic Fiber
A light weight, low density fiber, typically used as a high temperature insulation or a refractory
Ceramic Post Terminal Insulators
Used to cover the terminals of common strip heaters to prevent personnel contact with electrical hazards. Sold in pairs.
Chatter
The rapid cycling of a relay due to too narrow a bandwidth in the control.
Circuit
A complete or partial path over which current may flow.
Circuit breaker
A device that opens and closes a circuit by non-automatic means; it also opens the circuit automatically on a predetermined overcurrent (without damage to itself) when properly applied within its rating.
Cladding
An outer jacket, usually metallic, encasing the thermal insulation.
Classified locations
A location that is classified into a class, division, and group, or into a class, zone, and group, because a fire or explosion hazard may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or filings.
Closed Loop Control
A control system in which process temperature changes are detected by a sensor. The feedback from the sensor allows the control to make adjustments for accurate system regulation.
Cold Junction Compensation
A temperature sensitive device that prevents changes in the ambient temperature from affecting the cold junction of a thermocouple.
Cold lead
An electrically-insulated conductor that connects a heating cable–circuit conductor to the branch-circuit conductors; it does not produce any appreciable heat. Constant wattage heating cables require the use of cold leads.
Combustible dusts
Any finely divided solid material of 20 microns or less in diameter (i.e., material passing through a U.S. No. 40 Standard Sieve) that presents a fire or explosion hazard when dispersed and ignites in air or another gaseous oxidizer.
Combustible liquid
A liquid having a flash point at or above 100°F (37.8°C).
Comfort Heaters
Heaters, usually for the heating of areas to maintain comfort of the occupants. Generally, not for use in areas above 100°F. A wide variety of types (convection and fan forced) are available for use in ordinary, corrosive, and explosion hazard areas.
Common Mode Line Filter
A device to filter noise signals on both power lines with respect to ground.
Common Mode Rejection Ratio
The ability of an instrument to reject interference from a common voltage at the input terminals with relation to ground. Expressed in dB (decibels).
Compression Fittings
Bulkhead fittings designed for customer installation on round tubular heaters, to allow heaters to be mounted through the wall of a tank, duct, etc.
Conduction
One of the three methods of heat transfer (the others: radiation and convection). The transfer of heat by molecular motion without the bulk movement of material. Conduction is the only way that heat can be transferred within a solid.
Conductivity
The ability of heat or electricity to flow through a material.
Conductor
A long thin piece of metal used to carry current. An insulated conductor is a wire.
Conduit
Conduit is a housing used to protect wires and cables in an electrical system from damage and moisture. Conduit is made of PVC or metal and is available in various sizes.
Constant-wattage heating cable
Heating cables that have effectively the same power output over a large temperature range. Zone heating cables that use Nichrome® heating wires and most series resistance heating cables are examples of constant-wattage heating cables.
Contactor
A heavy-duty relay that controls electric power circuits.
Continuity
The presence of a complete path for current flow.
Continuity Check
A test that determines whether current can flow throughout the length of a circuit.
Continuous load
A load in which the maximum current is expected to continue for three hours or more.
Control Loop
The basic control loop of any automatic control system consists of: 1) variable (process) 2) sensor 3) error detector (of control) 4) control 5) final control element (relay, SSR, SCR) 6) temperature indication.
Control Mode
The method in which the control restores the system temperature to set point. On/Off, proportioning, and PID are the most common control modes.
Controller
A device that regulates the state of a system by comparing a signal from a sensor with a predetermined value and adjusts its output to the predetermined value. Controllers used in electric heat-tracing systems normally include some form of monitoring and alarming. Thermostats typically include little or no monitoring. Temperature sensors used with controllers are usually electronic (thermocouple, RTD, thermistor). Temperature sensors used with thermostats can be mechanical (bulb and capillary, bimetallic) or electronic.
Convection
One of the three methods of heat transfer (the others: conduction and radiation). The transfer of heat by the bulk motion of a fluid (liquid or gas). Convection is also the transfer of heat between a solid and a fluid.
Corrosive environment
An area where chemically-aggressive gases or liquids are present either in the pipe or in the surrounding atmosphere.
CPS
Cycles per Second (See Hertz).
CSA
Abbreviation for third party testing and approval agency, Canadian Standards Association
CSA International
CSA International is a leading provider of product testing and certification services worldwide. They test products for compliance to national and international standards and issue certification marks for qualified products across North America and around the world.
Current
Measured in amperes (A), is the flow of electricity. One ampere is one coulomb per second.
Current Limiting
A means to limit the current delivered to a load by a power control device, usually an SCR.
Current Proportioning
A 4-20 milliamp (typical) current output which provides a current proportional to the amount of control required.
Current Transformer
A transformer, usually toroidal (doughnut) shaped, designed to accommodate an electrical conductor, and provide a reduced, but linear output at a lower current, for instrument use. Typically specified by ratio i. e. 100:1
Cycle Rate (or Cycle Time)
In a time proportioning control, the period (usually in seconds) of time that is required to complete one on/off cycle once temperature has settled at the center of the proportioning band.
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D
Data Logging
Recording a process variable over an extended period of time.
Deadband
The range through which a measured signal can vary without initiating a response by the controlling device.
Deadleg
A segment of pipe that is designed to be in a permanent no-flow condition. This pipe section is often created for use as a control point for a larger system.
Default Parameters
The programming instructions permanently written in microprocessor software.
Definite Purpose Magnetic Contactor
Similar to a motor starter relay, for use with on-off controllers for slow processes. Available with optional enclosures for general, wet, and explosion proof areas.
Density
Mass per unit of volume, such as lbs./cu.ft.
Derivative
(See Rate)
Deviation
The difference between the selected value and the actual value.
Deviation Alarm
An offset value that follows the set point. If the set point is 300°F and the Deviation Alarm value is +20°F (or 320°F), then the set point is changed to 350°F, the Deviation Value alarm would be 350°F plus 20°F (or 370°F). See Process Alarm.
Deviation Meter
The display of process temperature on meter that indicates difference of or deviation of the process temperature from the set point.
di/dt
The rate of change of current vs. time. Filtering on large SCR units may be necessary to prevent damage from large current changes in small time periods
Dielectric
A material with a large resistance to the flow of electricity; an insulator.
Dielectric Strength
An amount of voltage that an insulating material can withstand before an electrical breakdown occurs.
Differential
In an on/off control, the temperature difference expressed in degrees between where the control switches off and the control switches on.
Differential Mode Line Filter
A device to filter noise signals between two power lines.
Digital Indication
The actual process temperature in indicated by LED or LCD display.
Digital Set Point
The desired temperature value is set by means of up-down pushbuttons or pushwheel switch.
Diode
A device that allows current to flow in only one direction.
Direct Current (DC)
An electric current flowing in one direction.
Disconnect
A control panel mounted main switch, which provides a means to turn off power in the panel before opening the door for servicing. Most disconnects do not provide overcurrent protection. This must be provided upstream using fuses or circuit breakers.
DOT (Demand Oriented Transfer)
An SCR power control system using the smallest time base possible. For example, 25% output would be 1 cycle on, and 3 cycles off.
Downspout
A Downspout channels the water gathered by rain gutters or a flat roof drain system down to the ground.
Drift
A change in a value over a long period due to changes in factors such as ambient temperature, time or line voltage.
Drip Edge
A drip edge is a type of flashing that is installed on the front edge of a roof to prevent water from seeping back under the roofing material.
Droop
In time proportioning controls, the difference in temperature between the set point and where the system temperature stabilizes. Corrected by automatic or manual reset.
DTS
Distributed Temperature Sensing (DTS) is a method of monitoring temperature along the continuous length of a pipeline. It provides a temperature profile for the full length of the pipeline for better visibility of hot/cold spots than can be provided by widely spaced RTD’s.
Dual Output
The primary control output will regulate the process temperature. A secondary control output will be utilized for process cooling or as an alarm.
Duty Cycle
The ratio of on time to on time plus off time, expressed as a percentage.
dv/dt transient protection
Filtering to limit voltage vs. time presented to an SCR. Helps protect SCR’s against transient voltages.
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E
Eave
An eave is the overhang on a roof which protects the building from weather damage. It is especially prone to ice dams and icicles which can cause water damage to a building.
Efficiency
The amount of useful output versus energy input, expressed as a percentage.
Electric heat-tracing system
A system of electric heating cables, connection kits, and a power distribution system that may include cables, panelboards, and transformers whose purpose is to maintain a piping system at or above a given temperature. The system may also include a control system with sensors, alarms, and controllers. Electric heat-tracing systems are sometimes referred to as electric pipe heating of trace-heating systems.
Electrical insulation (cable)
The part of the cable that consists of dielectric (see above) material.
Electromagnetic Interference (EMI)
Electrical and magnetic “noise” than can be generated when switching AC power. EMI can interfere with the operation of microprocessor based controls.
Electromechanical relay (EMR)
An electromechanical device that completes or interrupts a circuit by physically moving electrical contacts into or out of contact with each other. (See Contactor)
Emissivity
The ratio of radiant energy emitted from a surface compared to the radiant energy emitted from a black body at the same temperature.
Endothermic
A process is endothermic when it absorbs heat.
Equipment
A general term including material, fittings, devices, appliances, fixtures, apparatus, and the like used as part of, or in connection with, an electrical installation.
Error
The difference between the correct value and the reading or display value.
Event
A programmable On/Off output used to signal peripheral equipment or a process.
Exothermic
A process is exothermic when it generates heat.
Explosion-proof
A method of protection for electrical equipment used in Class I hazardous locations.
Explosion-proof apparatus
Is an apparatus enclosed in a housing that is capable of withstanding an explosion of a specified gas or vapor that may occur within it, and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.
Extension Wire
A wire intended to connect a sensor (typically a thermocouple or RTD) to a panel or control. Thermocouple wire must be same type as TC (J for J). RTD wire may be copper.
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F
Factory fabricated
A heating cable assembled by the manufacturer, including hot and cold end terminations and cold lead. Mineral insulated (MI) cable is generally factory fabricated. Self-regulating heating cables are generally not factory fabricated.
Fahrenheit
A temperature scale with 32°F defined as the ice point and 212°F as the boiling point of water at sea level.
Fault
A Fault is any condition that turns off the control unit and turns on the fault light. It most commonly occurs when one or more conductors of electric current short to each other or find a path to ground.
Fiber Optic Cables
Fiber Optic cables are traditionally used in telecommunications. However, they are being deployed as sensors for continuous temperature monitoring, leak detection and intrusion detection on pipelines in industrial applications. These fiber optic cables are specially armored for durability.
Field assembled
Heating cable supplied in bulk; terminating kits to be assembled (terminated) by field personnel.
Flash point
The minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid, as specified by tests.
Floor Temperature Sensor
A Floor Temperature Sensor is used in radiant floor heating applications to measure the temperature of a floor. It is used to activate a radiant floor heating system should the temperature of the floor drop below the desired temperature.
FM Approvals
FM Approvals offers worldwide quality management systems and certification and testing services of industrial and commercial products to national and international standards.
FM Approved
A product or system which has been evaluated by FM Approvals, and found to comply with a given standard or set of standards or has been evaluated for its use by utilizing accepted engineering practices and performance approaches.
Form A Relay
Single pole, single throw relay with Normally Open (NO) and common contacts. When coil is energized, the contacts will close.
Form B Relay
Single pole, single throw relay with Normally Closed (NC) and common contacts. Contacts are open when coil is energized.
Form C Relay
Single pole, double throw relay with Normally Open (NO), Normally Closed (NC) and common contacts. Can be selected as Form A or Form B contact.
Freezing Point
The temperature where a material changes from a liquid to a solid.
Frequency
The number of event occurrences or cycles over a specified period of time.
Fuse
An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcurrent through it. A fuse is a one-use device, unlike a circuit breaker, which can be reset and used many times.
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G
Ganging
The practice of combining multiple heating cables onto one branch circuit breaker.
Ground
The electrical line having the same potential as the surrounding earth; the negative side of a DC power supply; the reference point for an electrical system.
Ground fault
The passage of current from a circuit to earth-ground.
Ground-fault circuit breaker
A device that protects equipment; it turns off a circuit within an established period of time when a current to ground exceeds some predetermined value (usually from 5 to 100 mA) which is less than that required to operate the overcurrent protective device of the supply circuit.
Ground-fault circuit interrupter
A device intended for the protection of personnel; it turns off a circuit within an established period of time when a current to ground exceeds some predetermined value (usually 5 mA) which is less than that required to operate the overcurrent protective device of the supply circuit.
Ground-fault protection of equipment
A system that protects equipment from damaging line-to-ground-fault currents by disconnecting all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage from a supply circuit overcurrent device.
Grounded
Connected to earth or to some conducting body that serves in place of the earth.
Grounded Junction
A thermocouple junction in which the sheath and conductors are welded together forming a completely sealed integrated junction.
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H
Hazardous locations
Same as a classified location. A location that is classified into a class, division, and group, or into a class, zone, and group, because a fire or explosion hazard may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or Filings. For a more detailed description, refer to the National Electrical Code, Articles 500 through 503 in particular, as well as other related articles.
Hazardous locations divisions
Divisions 1 and 2 as defined in the National Electrical Code describe the likelihood that a flammable or combustible mixture will be present in ignitable quantity.
Hazardous locations groups
Groups A, B, C, D, E, F, and G in the National Electrical Code Article 500 classification system, and Groups IIA, IIB and IIC in the National Electrical Code Article 505 method of classification. For purposes of testing, approval, and area classification, various air mixtures (not oxygen-enriched) are grouped together because they have similar explosion characteristics.
Heat
Thermal energy expressed in Calories, Btu’s or Joules.
Heat loss
The rate of energy lost from a pipe, vessel, or equipment to the surrounding environment due to the difference in temperature between the pipe and the surrounding environment. The heat loss needs to be calculated because the heat tracing selected must be of sufficient power to replace the heat lost if the desired temperature is to be maintained.
Heat Loss Calculation
A heat loss calculation is determined by the type and amount of insulation and materials used to construct a building. It determines the ability of a building to hold heat in and calculates how much heat/energy must be put into a home to keep it warm.
Heat Offset
For some PID controllers; allows the creation of a dead area where neither heat nor cold is on, to prevent the process from oscillating between heat and cool. Saves energy.
Heat sink
A part that conducts and dissipates heat away from the pipe or equipment. Heat sinks can be pipe supports, valve operators, etc.
Heat Tracing
Heat applied to pipes or tanks usually by means of self-regulating cable, to replace heat lost through the insulation to the ambient.
Heat Transfer
A process of thermal energy flowing from one body to another. 1) Conduction: the transfer of heat from one particle of matter to another. 2) Convection: the transfer of heat from one part of a particle to another by the mixing of the warmer particles with the cooler. 3) Radiant: the transfer of heat from one body to another as the result of the bodies emitting and absorbing radiation energy.
Heat transfer aids
Thermally-conductive materials, such as metallic foils or heat transfer cements, used to increase the heat transfer rates from the heating cables to the process piping or equipment.
Heating cable circuit
A discrete length of heating cable that is directly wired to a single power connection kit at one end and terminated with an end seal kit. Intermediate branch heating cables (connected to the primary run of heating cable with a tee connection kit) are considered part of the heating cable circuit. Note that multiple-entry power connection kits will accommodate multiple heating
Hertz
Units of expression for frequency, measured in cycles per second.
High Temperature Wire
Special wire with high temperature insulation and nickel or nickel plated copper conductor. Can withstand higher temperatures than plastic insulated copper conductor wire used for general connections. Do not use tin plated copper lugs on high temp wire. They will oxidize and fail. High temperature terminations require special nickel or stainless steel lugs, if lugs are used.
High-limit temperature
The maximum allowable heat-tracing system temperature of the heat-traced equipment. A marking that indicates the maximum temperature that a piece of equipment will reach based upon a 104°F (40°C) ambient temperature. The temperature marking is compared to the ignition temperature of explosive gases, vapors, dusts, or filings that may be encountered in hazardous areas. Hi-Pot Test – the application of a high voltage to an electrical conductor to test the surrounding insulation.
Hopper Heaters
Modular heaters, consisting of tubular heating elements mounted to a metal plate, for attachment to hoppers. These are used to keep the walls above a critical temperature to prevent contents from sticking to or attacking the hopper.
Humidity Transmitter
An electronic device which provides a 4-20 mA signal based on the relative humidity sensed by the probe.
Hysteresis
The temperature sensitivity designed into the on/off control action between the on and off switching points. Expressed in percentage of control range. Also known as dead band.
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I
Ice Dam
An ice dam is ice that forms over the exterior wall of a building that prevents water, formed from melted snow and ice, from draining off the roof.
Ice Point
The temperature where pure water freezes (0°C or 32°F).
IECEx
IEC System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres.
IEEE
Institute of Electrical and Electronics Engineers is the world’s largest professional association for the advancement of innovation and technological excellence.
IEx
Institute of Certification - IEx is a Brazilian company with international renowned experts in electrical equipment for explosive atmospheres. IEx is accredited by INMETRO, National Institute of Metrology, Standardization and Industrial Quality, for hazardous locations products.
Impedance
The total opposition in a circuit to the flow of alternating current. Measured in ohms and represented by “Z”.
Input Scaling
Allows PID control to be adjusted to display inputs from transmitters (i.e. humidity), in appropriate engineering units.
Insulation
The term insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. Heat is transferred from one material to another by conduction, convection and/or radiation. Insulators minimize the transfer of heat energy. In home insulation, the R-value is an indication of how well a material insulates.
Insulation Resistance
Is the resistance of an insulator to current flow from a conductor (typically a heating element winding) to ground (the sheath). Usually measured by the application of a voltage, and measuring the resulting current. The resultant resistance, which is expressed in ohms, is calculated by the formula: R= V / I.
Insulation, Electrical
A substance which surrounds an electrical conductor, to prevent current from flowing to or leaking to ground or to other conductors.
Insulation, Thermal
A material which reduces heat flow from heated areas or objects to colder objects to conserve energy improve performance, or prevent operator contact with hot objects.
Integral
(See Automatic Reset)
Intrinsic Safety Barriers
Devices that limit current voltage and total energy delivered to a sensor or other instrument located in a hazardous area.
Intrinsically Safe Equipment and Wiring
Products that are not capable of releasing sufficient energy in a circuit to ignite a flammable atmosphere in a hazardous area.
Isometric
An engineering drawing: a three-dimensional view of the object or system.
Isothermal
A process or area that maintains a constant temperature.
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J
Jacket
A thermoplastic or thermosetting plastic covering, sometimes fabric-reinforced, applied over the insulation, core, metallic sheath, or armor of a cable.
Joule
The basic unit of thermal energy. 1 Joule equals 1 ampere passed through a resistance of 1 ohm for 1 second.
Joule effect
The heating effect produced by the flow of current through resistance.
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K
Kelvin
The unit of absolute or thermodynamic temperature scale. Zero Kelvin is absolute zero, where all molecular activity stops. No ° symbol is used. 0°C = 273.15K; 100°C = 373.15K.
Kilowatt (kw)
1000 watts or 3412 Btu per hour.
Kilowatt Hour
Electrical unit of energy expended by one kilowatt in one hour.
kVA (kilovolt Ampere)
A kilovolt ampere is a rating used for certain devices operating off of alternating current. It is in essence the number of “apparent” watts that that device is rated for.
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L
Lag
The time delay from application of heat until the process reaches temperature or the delay in a controller responding to a temperature change.
Lagging
(See Cladding)
Least Significant Digit
The digit farthest to the right in a display.
Light Emitting Diode (LED)
A solid state device which produces light from the flow of electric current through a semiconductor. These are individual indicating lights or segmented readouts used to display temperature.
Linearity
The compliance of an instrument’s response to a straight line.
Liquid Level Control
Detects liquid level below a reference depth. Can be used for replenishment or to turn off a heater to prevent damage.
Listed
In accordance with the National Electrical Code and other NFPA standards this means equipment or materials included in a list published by an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of listed equipment or material, and whose listing states either that the equipment or material meets appropriate designated standards or has been tested and found suitable for use in a specified manner.
Load
The electrical demand of a process expressed as wattage, amps or resistance (ohms).
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M
Maintain temperature
Specified temperature of the fluid or process material that the heat tracing is designed to hold at equilibrium under specified design conditions, normally at minimum ambient temperature.
Manual Reset
The adjustment on a proportional control which shifts the proportioning band in relation to the set point to eliminate droop or offset errors.
Maximum ambient temperature
Highest expected environmental temperature surrounding the heat-traced object.
Maximum contact temperature
The maximum withstand temperature of the heat traced plastic pipe. The temperature depends on its pressure rating and material.
Maximum equilibrium temperature
The highest equilibrium pipe temperature that occurs when the heating cable is continuously energized at the maximum ambient temperature (defined as runaway pipe temperature by IEEE 515).
Maximum intermittent exposure temperature
The highest temperature to which the heating cable may be exposed intermittently. (power on or off) Defined as high-temperature excursions of not more than 48 hours in duration, with total cumulative exposure of less than 1000 hours. Intermittent high-temperature exposure may occur during process upset conditions or steam-cleaning operations.
Maximum maintain temperature
The highest temperature at which the heating cable may be operated continuously (power on).
Maximum operating temperature
The maximum temperature of the process fluid during normal continuous operation. This temperature may be the same as the maintain temperature, but it is sometimes substantially higher. This is assumed to be the highest temperature to which the heating cable will be continuously exposed.
Mean Temperature
The maximum and minimum temperature average of a process at equilibrium.
Mechanical Relay
An electromechanical device that completes or breaks a circuit by closing or opening electrical contacts.
Mercury Contactor (Mercury Displacement Relay)
A mechanical relay with mercury as the current carrying conductor. They are faster, quieter, and last longer than conventional mechanical contactors. Contains mercury, a hazardous substance, not permitted in some plants.
Metal Drip Edge
A metal drip edge helps to prevent water from seeping back under the shingles. It is placed along the edge of a roof.
MI Cable (Mineral Insulated Cable)
Refers to metal sheath heat trace cable, having internal magnesium oxide insulation between the conductor(s) and the sheath. Especially suited for high temperature operation, and is mechanically rugged. All MI cables are made to order.
Microprocessor
The central processing unit (CPU) that performs the logic operations in a micro-computer system. The microprocessor in a process or instrument control decodes instructions from the stored program, performs algorithmic and logic functions, and produces signals and commands.
Milliamp
(one thousandth of an amp).
Millivolt
(one thousandth of a volt)
Minimum ambient temperature
The lowest expected ambient temperature at the design location. The effect of wind is covered in the design. The wind chill factor should not be used.
Minimum operating temperature
The lowest process-operating temperature of the fluid during flow conditions. This temperature is frequently the same as the design maintain temperature.
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N
NEC (National Electrical Code)
Regulations and specifications for wiring as published by the National Fire Protection Association, Inc.
Negative temperature coefficient
A device or material whose resistance decreases with an increase in temperature and increases with a decrease in temperature. A thermistor generally has a negative temperature coefficient.
NEMA
National Electrical Manufacturer’s Association Noise – undesirable electrical interference on the signal wires.
NFPA
National Fire Protection Association is an international nonprofit organization established in 1896. The company’s mission is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating consensus codes and standards, research, training and education.
Noise Suppression
A device used to reduce electrical interference.
Noncorrosive environment
An area where chemically-aggressive gases, vapors, or fluids are not present.
Normal Mode Rejection Ratio
The ability of an instrument to reject interference of the line frequency (50-60Hz) across the input terminals.
nVent
The global leader of inventive electrical solutions that connect and protect customers by creating safer systems to ensure a more secure world. The Thermal Management segment consists of heat tracing solutions and complete heat management systems.
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O
Offset
The difference in temperature between the set point and the actual process temperature.
OHM
The unit of electric resistance.
On-Off
A control whose action is full on or full off.
Open Loop Control
A control system with no sensing feedback.
Open Sensor Output Command
For some PID controls, allows selection of shut down or switch to pre-assigned power output (i.e. 30%), in the event of an open sensor.
OSHA
US Government agency, Occupational Safety and Health Administration (or Agency). Specifies and enforces safety in the workplace.
Outdoor location
The installation is subjected to environmental extremes, including exposure to a high wind velocity (assumed to be 20 mph [32 km/h] for an insulated, heat-traced pipe).
Output Limit
For some PID controls, allows selection of a maximum percent of full power. Useful of heater is oversized, or for fast heat up followed by close control.
Overcurrent
Any current more than the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault. A current more than rating may be accommodated by certain conductors for a given set of conditions. Hence, the rules for overcurrent protection are specific to particular situations.
Overcurrent protective device
An in-line component of an electric circuit used to cause and maintain the interruption of current flow to the protected device when the protected device is subjected to an overcurrent condition (e.g., circuit breaker, fuse).
Overload
Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity when, if it persists for a sufficient length of time, it would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload.
Overshoot
Excursion of temperature above the set point.
Oversize insulation
A term applied to thermal insulation when the thermal insulation inner diameter must be larger than the nominal outer diameter of a particular pipe in order to accommodate the heating cable.
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P
P & ID
Piping and instrumentation diagram.
Panelboard
A single panel or group of panel units assembled in a single panel that includes buses, and automatic overcurrent devices. A panelboard may or may not have switches for the control of light, heat, or power circuits. Designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front.
Parallel heating cable
A heating cable with heating elements that are electrically connected in parallel, either continuously or in zones, such that watt density per linear length is approximately equal along the length of the heating cable (allowing for the drop in voltage down the length of the heating cable).
Percentage Timing Input Controllers
Are motor driven adjustable duration cam devices. These provide an adjustable duty cycle, for a time base of 15 or 30 seconds. Useful for intensity (open loop) control. Not for use with tungsten quartz radiant heaters.
Phase
Time based relationship between an intermittent function and a reference. Electrically, the expression is in angular degrees to describe the voltage or current relationship of two alternating waveforms.
Phase Angle Control
SCR firing mode in which the SCR’s are turned on for a portion of each half cycle. Necessary for high inrush and/or inductive loads, such as tungsten (quartz lamp) heaters and transformers.
Phase Proportioning
A temperature control form where the power supplied to the process is controlled by limiting the phase angle of the line voltage.
PID
Three mode temperature control–proportional, integral (automatic reset), derivative (rate).
Pipe schedule
An index that specifies the nominal wall thickness as a function of pipe size.
Pipe size
The nominal diameter of the pipe. For tubing, the size and outside diameter are the same.
Pipe support
A device for supporting a section of pipe.
Pitch
The degree of slope or the distance between two points of a spiraled heating cable.
PLI (Power Line carrier Interface)
A set of components that provide temperature monitoring capability for heat-tracing control & monitoring systems by communicating the temperature data to the control system using the heat tracing and power distribution wiring thus eliminating the need for RTD wiring.
Plot plan
A representation of the layout of a particular facility or area. It typically shows the position of roads, buildings and other constructions inside an industrial plant with their coordinate lines. Polarity – having two oppositely charged poles; one positive, one negative.
Pole, Single and Double
A single pole breaker is the breaker used for 110 volt power. A double pole breaker is for 220 volt power. It is designed as two single pole breakers connected together and feeds two sources of 110 volt power into one to make 220 volts. It is designed so that if one of the two 110 volt breakers trip, it will automatically trip the second.
Positive temperature coefficient (PTC)
A characteristic of a device or material whose resistance increases with an increase in temperature and decreases with a decrease in temperature. Self-regulating heating cables have positive temperature coefficients and are often referred to as PTC heating cables.
Potting
The sealing of components with a compound such as epoxy to protect against moisture and other contaminants.
Power-limiting heating cable
A type of heating cable that shows PTC behavior based on the properties of a metallic heating element. The PTC behavior exhibited is much less (a smaller change in resistance in response to a change in temperature) than that shown by self-regulating heating cables.
Process Alarm
A fixed alarm or secondary set point value independent of the primary set point. Should a process value exceed this value, an alarm condition would register.
Process control
These terms are generally used to denote any heat-tracing application other than (also process-temperature control) freeze protection of water lines.
Process operating temperature
The maximum temperature of the process fluid during normal continuous operation. This temperature may be the same as the maintain temperature, but it is sometimes substantially higher. This is assumed to be the highest temperature to which the heating cable will be continuously exposed.
Process Value
The indicated value of the parameter being measured/controlled.
Process Variable
The parameter being controlled or measured such as temperature, relative humidity, flow, level, pressure, etc.
Programmable Thermostat
A programmable thermostat is a thermostat which is designed to adjust the temperature according to a series of programmed settings that take effect at different times of the day. Programmable thermostats may also be called setback thermostats or clock thermostats.
Proportioning Band
The temperature band in degrees within which a control’s proportioning function is active. The width is usually adjustable, and is expressed in degrees or as a percent of span.
Proportioning Control Mode
When process temperature approaches set point and enters the proportioning band, the output is switched on and off at the established cycle time. The change in power to the load provides a throttling action which results in less temperature overshoot. This cycling will continue until on and off times are equal.
Protection Head
A junction box for the protection of the sensor to extension wire connection. Protection heads can provide mechanical, moisture, and explosion area protection.
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R
Radiation
One of the three methods of heat transfer (the others: conduction and convection). The transfer of heat by the propagation of energy waves. When dealing with insulated pipes and vessels the effect of radiation is usually insignificant.
Ramp
A programmed rise in temperature.
Range
An area between two limits in which a measurement or control action takes place. Typically expressed in upper and lower limits.
Rankine
An absolute temperature scale based upon the Fahrenheit scale with 180° between the ice point and boiling point of water. 0°F = 459.67°R.
Rate (derivative)
A control function that measures the rate of increase or decrease of the system temperature and brings the control into an accelerated proportioning action. This mode prevents an overshoot condition at initial heat-up and with system disturbances.
Rate Time
The interval over which the system temperature is sampled for the derivative function.
Rated output
The expected minimum power output of a heating cable for a given set of conditions. These conditions may include applied voltage, pipe or surface temperature, and total length.
Rated voltage
The voltage to which operating and performance characteristics of heating cables are referenced.
Redundant or Redundancy
The introduction of auxiliary elements and components to a system to perform the same function as other elements in the system for the purpose of improving reliability. Redundant electric heat-tracing systems consist of duplicate independent heating cables and controllers, each with its own sensor supplied from separate power systems, all independent of each other but all applied to the same mechanical piping, valves, tanks, etc.
Remote Setpoint
On some controllers, an external 4-20 mA signal, or similar, will change the setpoint of a control. Good for remote computer system control or cascading.
Remote Shutdown
A feature on some SCR units, permitting the shutdown of output from a remote contact opening or closing.
Repeatability
The ability to give the same output or measurement under repeated identical conditions.
Resistance
Electrical resistance is a measure of the degree to which an object opposes an electric current through it. The SI unit of electrical resistance is the ohm.
Resolution Sensitivity
The amount of temperature change that must occur before the control will actuate. It may be expressed in temperature or as a percentage of the control’s scale.
Response Time
In analog instruments, the time required for a change of the measured quantity to change the indication. In sensors, the time required to reach 63.2% of the step change.
Retransmit Output
Analog output scaled to the process or the set point value.
RMM2
Remote Monitoring Module which aggregates RTD temperature data in the field and sends it over one wire pair to the control & monitoring panel. This allows reduction of RTD wiring runs in the field while ensuring all temperature data is provided to the heat tracing control & monitoring system.
Routine test
A test carried out by the manufacturer of the heating cable during production.
RS232 or RS 422-485 Input/Output Signal
A serial interface suitable for connection between a digital control and a personal computer, a host computer or printer.
RTD
A temperature sensing probe of finely wound platinum wire that has a linear resistance change for a corresponding temperature change. The resistance increases as the temperature rises. A base resistance of 100 ohms at 32°F is the industry (DIN) standard.
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S
Saturation Temperature
The boiling temperature of a liquid at the existing pressure.
SCFM
Volumetric flow rate in cubic feet per minute at 60°F (15°C) and standard atmospheric pressure.
Schematic
A diagram that represents the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension.
SCR
Silicon Controlled Rectifier
Self-regulating
The inherent capability of polymer-core heating cables to inversely vary their power output in response to an increase or decrease in the actual temperature in the immediate vicinity of the heating cable.
Self-tune
An internal program in some PID controllers, which allows the control to experience the process and internally calculate parameters to obtain good process control operation.
Sensor
The first system element that responds quantitatively and performs the initial measurement. In electrical heat-tracing systems, sensors respond to the temperature of the system and may be directly connected to controllers. Sensors can be mechanical (bulb and bellows, bimetallic) or electrical (thermocouple, RTD, thermistor).
Sensor Breakdown Protection
Circuitry which ensures safe process shut down in the event of sensor failure.
Sensor Selection
A menu or hardware feature on most indicating controls which allows selection of a number of thermocouple types, RTD’s and /or other sensors
Sensor, In floor
A sensor that is installed into a floor to monitor its temperature. It is particularly common in radiant heating applications because of its ability to sense floor temperature.
Sensor, Moisture/Temperature
A sensor that is used in snow/ice melting applications to monitor the exterior temperature and moisture content of the air. When moisture and a near freezing temperature are sensed, the sensor activates the snow melting systems before snow and ice accumulate.
Serial Communications
A method of transmitting data between devices.
Serial Interface
The hardware and wiring to connect control(s) with digital communications to a computer. Typical choices are RS232 (single drop), RS 422, 458 (multi-drop).
Series heating cable
A heating cable using a high resistance wire in order to create heat via electrical resistance. These cables provide a constant heat output and cannot be overlapped.
SES
Smart End Seal transmitter that enables monitoring signals to transmit through heating cable bus wires and power cables. No additional field wire is necessary. Part of the Power Line Carrier Interface (PLI) option on certain Raychem control & monitoring systems.
Set Point
Control setting to achieve or maintain temperature.
Sheath
The outer shell of a heating element, usually metal. Typical materials are: copper, steel, stainless steel alloys, and others. Provides mechanical protection and a ground path.
Sheath temperature
The temperature of the outermost heating cable jacket covering that may be exposed to the surrounding atmosphere.
Shield
Material surrounding a conductor(s) to prevent interference of electrostatic or EMI from external sources.
Short circuit
A fault consisting of a lower-resistance connection across a voltage source, which normally results in an excessive current. It should cause the overcurrent device (circuit breaker or fuse) to open.
Shorted SCR Detection
Circuitry in some SCR’s to detect a shorted SCR in a power control module. Usually the output can be an alarm to alert operator that unit needs service.
Shunt Trip
A coil, designed to turn off the main disconnect on a panel, when energized. Typically used for large SCR panels, to drop the load if high limit is reached.
Silicon-controlled rectifier (SCR)
A four-layer semi conductive device that is used as an electrical switch in ac and dc circuits. An activation signal is required to turn the SCR on or off.
Skin Effect
The phenomena which results from AC Current traveling through a wire located inside a ferromagnetic metal tube in which the return current flowing in the metal tube limits the current flow to the inside surface of the metal tube. No current or voltage potential exists on the outside of the tube.
Snow Load
Snow Load is the force exerted on roof structures by the weight of accumulated ice and snow. Snow Load requirements vary dramatically by geographic location of the project, characteristics of the building or its location that influence the accumulation of snow and ice on the roof structure and the water content of the snow.
Soak
To raise the temperature of a metal object in a heated environment to produce a metallurgical change. Also, a pre-programmed time to provide a set point to a process, as used in a ramp-soak program.
Soft Start
Reduces voltage on initial start-up which reduces power to the heaters.
Solid-state relay (SSR)
A solid-state switching device that completes or interrupts a circuit electrically. An SSR has no moving parts.
Span
The difference between the upper and lower limits of a controller’s range.
SPC
Smart Power Connector is part of the Power Line Carrier Interface (PLI) option which allows MI and VPL technology heating cables to be used with the PLI option on certain Raychem control & monitoring systems. The SPC takes the place of the power connection kit.
Specific Heat
The ratio of thermal energy required to raise the temperature of a mass of material 1 degree to the thermal energy required to raise an equal mass of water 1 degree.
Speed of Response
Time needed for a temperature change occurring at the sensor to be translated into a control action.
Stability
The ability of an instrument or sensor to maintain a constant output when a constant input is applied.
Standard
Reference point from which references or calibrations are made.
Start-up current
The initial current drawn by a heating cable when it is energized at the start-up temperature.
Start-up temperature
The lowest temperature expected at a time when the heat-tracing cable will be switched on. This can be an important design consideration for self-regulating cables because the start-up current depends on the start-up temperature.
STS
Raychem’s Skin-effect heat Tracing System (STS) is a pipe heating technology designed for long pipeline applications. It is capable of providing high heating power to over 25Km of pipeline between power points.
Surge Current
A higher than nominal current of short duration occurring when power is initially applied to loads such as self regulating heat cable and tungsten filament quartz radiant heaters.
System limit temperature
The highest temperature that the heat-tracing system is allowed to impose on the rest of the system. For example, a plastic pipe system will have a relatively low system limit temperature to protect the plastic pipe. A temperature-sensitive fluid will have a system limit temperature to protect the fluid from high temperatures from the heating cable.
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T
Temperature Gradient
The range of temperature variations at various physical locations throughout a thermal system.
Thermal Conductivity
The property of a material to conduct heat.
Thermal Expansion
An increase in size due to an increase in temperature.
Thermal insulation
Material that is designed to have a low thermal conductivity. Thermal insulation is placed on the outside of pipes and vessels to reduce the rate of heat loss.
Thermal Lag
The time delay in the distribution of heat throughout a thermal system.
Thermal System
A series of components arranged and designed to provide heat. The four elements or components compromising a Thermal System are: 1) work or load 2) heat source 3) heat transfer medium 4) control system
Thermistor
A temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance in response to a small change in temperature. Thermistors usually have negative temperature coefficients.
Thermocouple
A temperature-measuring device consisting of two wires of dissimilar metals. The voltage difference across the wires can be related to the difference in the temperature of the two junctions.
Thermostat
A device that senses temperature and activates a relay to control the flow of current to a downstream device.
Touch 1500
A state-of-the-art user interface using a 15-inch (381 mm) color display with touch screen for the Raychem NGC-40 system.
Touch Safe Design
Optional shields available on some SCR power control modules, reduce the possibility of personnel coming in contact with high voltage.
TraceCalc Pro
Pentair Industrial Heat Tracing Solutions' heat-tracing system design software. Performs thermal calculations, selects products, and generates the required Bill of Materials based upon the input design parameters.
Transducer
A device that converts a measured variable into another form which is the transducer’s output. A thermocouple transforms heat to a millivolt output.
Transformer
A transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling without requiring relative motion between its parts. It usually comprises two or more coupled windings, and, in most cases, a core to concentrate magnetic flux. An alternating voltage applied to one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Varying the relative number of turns between primary and secondary windings determines the ratio of the input and output voltages, thus transforming the voltage by stepping it up or down between circuits.
Transmitter
A device used to transmit temperature data from the sensor.
Turnkey installation
Complete, cost-effective installation using front-line, direct-hire labor. Includes complete documentation of the system.
Type test
A test or series of tests carried out on equipment; representative of a type, to determine compliance of the design, construction, and manufacturing methods within specified requirements.
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U
UIT2
User Interface Terminal. This is the touch screen display used for local control and monitoring of Raychem NGC-30 controllers.
UL
Underwriters' Laboratories is an independent product safety certification organization that tests products and writes standards for the safety of commercial and industrial products.
Undershoot
Excursion of temperature below set point.
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V
Valley
A valley is a location on a roof where two roof sections meet together forming a concave joint. Valleys are especially susceptible to ice dams and often need some form of ice melting system.
Valley Metal
Valley Metal is flashing that is placed in a valley to prevent leaking from occurring.
Volatile flammable liquid
A flammable liquid having a flash point below 100°F (38°C), or a flammable liquid whose temperature is above its flash point, or a combustible liquid having a vapor pressure exceeding 40 psia at 100°F (38°C) whose temperature is above its flash point.
Volt
The volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force.
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W
Watt-density
Thermal output of heating cable in watts per unit area.
Wattage
A unit of measurement of electrical power. In a resistive circuit, VI = W (See Ohms Law formulas).
Weather barrier
A material or materials, which, when installed on the outer surface of thermal insulation, protects the insulation from the weather, such as rain, snow, sleet, wind, solar radiation, or atmospheric contamination and physical damage.
Welded
One common method of attaching sensor probe to threaded hub. Welding produces a moisture proof, mechanically strong bond.
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Z
Zero Voltage (or Zero Crossover) Switching
Completing or breaking of a circuit when the voltage wave form crosses zero voltage.
Zone
Zone refers to the area that is covered by each individual control unit in an electric radiant heating system. The larger the area to be heated, the more zones that will be installed.
Zone heating cable
A parallel resistance heating cable which uses a resistive element between the bus wires to act as a heater. The resistive element makes contact with alternate bus wires at a distance called the zone length.
Zoned Heating
Zoned Heating allows for temperature variability throughout a building or home. Zoned heating uses numerous zones, each with their own activation device. Each zone can then be adjusted to the desired temperature.
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