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.
Control Accuracy – maintaining a process at the desired setting.
The errors or combination of errors in the entire system including the sensor, control,
power, load and design inefficiencies effect control accuracy.
Display Accuracy – the amount of potential error between a measured
value and the control’s displayed value.
Set Point Accuracy – the potential error between a measured value
and the control setting.
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.
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.
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.
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.
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.
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.
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.
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.
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).
BTU – British Thermal Unit; the amount of thermal energy required
to raise one pound of water, 1°F .
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.
Bulkhead Threaded Fittings – available on tubular heaters, factory
brazed, to allow heaters to be mounted through the wall of a tank or duct, etc.
Bumpless Transfer – The smooth, automatic transition from automatic
control (closed loop) to manual control (open Loop). The control output is maintained
during the transfer.
Burst Firing – a fast cycling control output, typically 3-32VDC,
used in conjunction with a solid state relay.
C
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
Cartridge and Immersion Temperature Controllers – are mechanical
Thermostats with operation based on the difference of expansion of different metals.
Cartridge Heaters – cylindrical heaters with leads exiting one
end. Most often inserted in drilled holes in platens and molds to heat blocks of
metal. A variety of standard diameters, lengths and wattages are available, as
well as special lengths, electrical ratings, and lead wire options.
Cascade – Control function where the output of one control loop
provides the set point for a second loop, which determines the control action.
CE – A mark that designates compliance with European Union (EU)
requirements for products sold in Europe
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 Beads – beads of ceramic material, with various hole sizes,
intended to insulate bare high temperature wire, to prevent short circuits.
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.
cfm – the volumetric flow rate of a liquid or gas in cubic feet
per minute.
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.
Circulation Heaters – heaters for fluids or gasses consisting of
an insulated pipe body with an immersion heater inside. Various sheath and pipe
body materials are offered to heat a variety of material to a range of temperatures.
Mechanical thermostats are included on some models. Options include mechanical or
electrical controls, built-in sensors, baffles, and ASME design and certification.
Complete skid mounted systems with panels are also available.
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 Length – the distance from the end of the sheath to the heated
section of a tubular or other similar heater.
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 – the transfer of heat from one material at a given
temperature to another material at a lower temperature, while in direct contact
with each other.
Conductivity – the ability of heat or electricity to flow through
a material.
Constant Wattage – refers to a type of heat trace cable having
a constant wattage output regardless of the surrounding temperature.
Continuity Check – A test that determines whether current can flow
throughout the length of a circuit.
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.
Control Type – options are direct acting (cooling) and reverse
acting (heating).
Convection – the transfer of heat from a source or higher temperature
area in a gas or liquid by the movement and mixing of the masses.
CSA – abbreviation for third party testing and approval agency,
Canadian Standards Association
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.
CPS – Cycles per Second (See Hertz).
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.
D
Data Logging – Recording a process variable over an extended period
of time.
Dead Band (differential) – is the difference in degrees between
temperature control turn on and turn off. This parameter is for on-off controls.
It also applies to overtemperature controls.
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 – an electrical insulator - a material with low electrical
conductivity.
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.
DIN – Deutsche Industrial Norms, a German agency that sets engineering
standards. Control panel hole size cutouts are typically based on DIN dimensions
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.
Dishwasher Heaters – immersion heaters with terminal housing and
built-in controls, designed for use in commercial dishwashers
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.
Drift – a change in a value over a long period due to changes in
factors such as ambient temperature, time or line voltage.
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.
Drum Heaters – flexible heaters designed to heat or maintain the
temperature of standard 5, 16, 30 and 55 gallon drums. A selection of ratings are
available, some with thermostats.
Dry Well Heater – a heater designed to be installed in a dry area,
usually a pipe, to heat the pipe, with the ultimate purpose of heating liquid surrounding
the pipe.
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.
E
Efficiency – the amount of useful output versus energy input, expressed
as a percentage.
Electric Stud Heater – a long cylindrical heater designed to be
inserted into the hollow bolts of large machinery to obtain “shrink fit tightness”
when the bolts cool.
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.
Element Clamps – cast iron clamps are offered to clamp strip and
ring heaters to surfaces for conduction heating of tanks, etc.
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.
Enthalpy – the sum of the internal energy of a body and the product
of its volume multiplied by the pressure used to evaluate the energy change occurring
when a vapor or gas is heated. Expressed in units of Btu/lb. or Joules/gram.
Error – the difference between the correct value and the reading
or display value.
Exothermic – a process is exothermic when it generates heat.
Explosion Proof Strip Heater – used to heat by conduction in areas
with explosion hazards.
Explosion Proof Terminal Housing (or Enclosure) – an enclosure,
housing, or panel which will contain a internal gas explosion. This prevents an
explosion from setting off surrounding area. Housing contents must not produce surface
temperature which would ignite flammable gases or vapors in the vicinity.
Extension Wire – 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.
External Interlock – provided on most Chromalox panels, the interlock
is a jumper, which turns off the load when interrupted. Typically connected to a
flow or pressure switch for moving systems to protect against a no flow condition.
Event – a programmable On/Off output used to signal peripheral
equipment or a process.
F
Fahrenheit – a temperature scale with 32°F defined as the ice point
and 212°F as the boiling point of water at sea level.
Flanged Immersion Heaters – immersion heaters with mounting flanges
(ANSI standard and others). Most offer a choice of terminal housings for various
environments. Optional sheath thermocouples are also available.
Flexible Heaters – available in many standard sizes and ratings,
most are constructed of silicone rubber, with internal winding. Specials with accessories
such as thermostats, cords and plugs are available, as well as unique shapes.
Flow Rate – speed or velocity of fluid movement.
FM (Factory Mutual Research Corporation) – a third party approval
agency, which tests and approves equipment for service in various areas and conditions.
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.
fpm – flow velocity in feet per minute.
fps – flow velocity in feet per second.
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 – A device that interrupts power in a circuit when an overload
occurs.
Fuzzy Logic – An artificial intelligence technique that allows
control decisions to be made upon approximate or incomplete information. It is a
continuous decision making function that can prevent initial overshoot and set point
differentials.
G
GFCI – (Ground Fault Circuit Interrupter) – an electronic circuit
which monitors the current flow from a conductor to a ground reference. When the
current exceeds a predetermined value, the GFCI shuts the circuit down.
GIGA – the prefix for one billion (G).
gph – the volumetric flow rate in gallons per hour.
gpm – the volumetric flow rate in gallons per minute.
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.
Grounded Junction – A thermocouple junction in which the sheath
and conductors are welded together forming a completely sealed integrated junction.
H
Heat – thermal energy expressed in Calories, Btu’s or Joules.
Heat Balance – proper sizing of the heat source to the requirements
of the system (including heat losses).
Heat Exchangers – metal tubes or plastic coils designed to heat
or cool solutions by immersion, with a fluid (or steam) circulating through the
coil to obtain the desired effect.
Heat of Fusion – the amount of energy required to change one pound
of a material from a solid to a liquid without an increase in temperature. Expressed
in Btu/lb.
Heat of Vaporization – the amount of energy required to change
one pound of a material from a liquid to a vapor without an increase in temperature.
Expressed in Btu/lb.
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 – in power control, an array of plates or fins, usually
aluminum, which conducts heat away from the power control devices (SCR’s) and dissipates
the heat by free or forced convection.
Heat Tracing – heat applied to pipes or tanks, 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 and Release Coating – a compound designed to be applied
between heaters and the surfaces being heated to improve heat transfer. Also makes
cartridge heaters easier to remove from drilled holes.
Heat Transfer Fluid Vaporizer – a vaporizer for heat transfer fluids,
to obtain improved process heat transfer by recovery of the heat of vaporization.
Heat Transfer Medium – a gas, liquid or solid through which heat
flows from the heat source to the work.
Heat Transfer Systems – consist of circulation heater(s), pump,
control panel and related items, ready to connect to your service and process. Oil
and water systems are available, in many sizes with a host of features and accessories.
Helically Coiled Resistance Wire – a coil of Nichrome wire, wound
in a helix, which is the resistance winding of the heater.
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.
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.
I
Ice Point – the temperature where pure water freezes (0°C or 32°F).
Immersion Heaters – heating elements designed to heat a fluid or
gas by direct contact.
Impedance – the total opposition in a circuit to the flow of alternating
current. Measured in ohms and represented by “Z”.
Infrared – or radiation is the exchange of energy by electromagnetic
waves. The infrared spectrum extends from the deep red end of the visible spectrum
to the microwave region of the radio spectrum, The portion adjacent to the visible
spectrum is of importance to heating. Radiant heat transfer can be very efficient
in directing energy from the heat source to an object.
Insulation, Electrical – a substance which surrounds an electrical
conductor, to prevent current from flowing to or leaking to ground or to other conductors.
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, 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.
Input Scaling – allows PID control to be adjusted to display inputs
from transmitters (i.e. humidity), in appropriate engineering units.
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.
Isothermal – a process or area that maintains a constant temperature.
J
Joule – the basic unit of thermal energy. 1 Joule equals 1 ampere
passed through a resistance of 1 ohm for 1 second.
Junction – A thermocouple junction is the point at which two alloys
are joined. A typical thermocouple circuit would have a measuring and a reference
junction.
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.
Kilo – the metric prefix for one thousand (K).
Kilowatt (kw) – 1000 watts or 3412 Btu per hour.
Kilowatt Hour – electrical unit of energy expended by one kilowatt in one hour.
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.
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.
Load – the electrical demand of a process expressed as wattage,
amps or resistance (ohms).
M
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.
Mass Flow Rate – weight of a substance flowing per unit of time
past a specific cross-sectional area within a system.
Maximum Allowable Load Resistance – the maximum resistance (in
ohms) into which a control can deliver specified current. Usually specified for
4–20mA outputs, and is limited by internal control supply voltage.
Mean Temperature – the maximum and minimum temperature average
of a process at equilibrium.
Measuring Junction – the thermocouple junction at the point of
measurement in the process.
Mechanical Relay – an electromechanical device that completes or
breaks a circuit by closing or opening electrical contacts.
Mega – the metric prefix for one million (M)
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.
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.
Micro – The metric prefix for one millionth Microamp (one millionth
of an amp).
Micron – (one millionth of a meter).
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.
Milli – The metric prefix for one thousandth
Milliamp – (one thousandth of an amp).
Millivolt – (one thousandth of a volt)
Moisture Resistant Terminal Housing – a terminal housing designed
to meet the requirements of NEMA 4. Chromalox types E2 and E4 meet these requirements.
MOV Protection – SCR protection provided by a Metal Oxide Varistor
(MOV), which clamps voltages at limits to stay below critical SCR failure values.
N
NEC (National Electrical Code) – regulations and specifications
for wiring as published by the National Fire Protection Association, Inc. NEMA
– National Electrical Manufacturer’s Association Noise –
undesirable electrical interference on the signal wires.
Noise Suppression – a device used to reduce electrical interference.
Normal Mode Rejection Ratio – the ability of an instrument to reject
interference of the line frequency (50-60Hz) across the input terminals.
NPT – National Pipe Thread
O
OCE (Open Coil Element) – heaters designed to be installed in 2
or 3 inch customer- supplied threaded schedule 40 dry well pipes to heat liquids
with the heat transferred through the pipe walls. Provides low watt density on the
pipe for viscous fluids, and allows for heater replacement without draining the
tank. Available terminal housings provide easy connections to heater with high temperature
wire. Not for use in explosion hazard areas.
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 Coil Elements – elements with the Nichrome resistance wire
exposed. Designed to heat by radiation and/or convection.
Open Coil Oven Elements – ribbon wound open coil elements designed
specifically for use in ovens.
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.
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.
OSHA – US Government agency, Occupational Safety and Health Administration
(or Agency). Specifies and enforces safety in the workplace.
Over-the side Immersion Heaters – immersion heaters
designed for use in open top tanks. A wide variety of sheath materials and coatings
are available to heat most solutions Risers to terminal housings are provided, as
well as optional mechanical thermostats for some models.
Overshoot – excursion of temperature above the set point.
P
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).
Polarity – having two oppositely charged poles; one positive, one
negative.
Potting – The sealing of components with a compound such as epoxy
to protect against moisture and other contaminants.
Process Air Heaters – component heaters or complete assemblies
for heating low pressure, high volume air for processes. Single elements of 475
watts to duct heaters of 300kw are included in the selection.
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 Radiant Heaters – heaters providing a variety of wavelengths
of radiant energy for heating processes, drying parts, freeze protection, etc. Many
types and sizes are available.
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.
Proportioning Band – (or proportional 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.
psia – pounds per square inch absolute. Pressure reference to a
vacuum.
psig – pound per square inch gauge. Pressure reference to ambient
air pressure.
Q
Quality of Steam – the relative amount of liquid present in saturated
steam as a percent of the total weight. The quality of steam is 100% less the percent
liquid. Dry saturated steam has a quality of 100%.
Quartz Lamp Radiant Heater – a heater in a reflector, using a tungsten
filament quartz tube heater for the radiant source. The best source when the heater
must be able to be turned off quickly when the line stops. Intensity control must
use phase angle fired SCR’s.
R
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.
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.
Repressed Bends – required when a tubular heater is bent to tighter
radius than permitted for customer bending. Repress dies restore the internal compaction
of the magnesium oxide to prevent voids, which may result in premature heater failure.
Resistance – the resistance to the flow of electric current measured
in ohms.
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.
Ring and Disc Heaters – component heaters which are flat and circular.
They are usually used to heat by clamp on conduction. Variety of sizes offered allows
for nesting.
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.
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.
SCR – Silicon Controlled Rectifier
Secondary Insulating Bushings – porcelain bushings designed to
allow certain strip heaters to be electrically isolated from ground, when using
on higher voltages for air heating. The heater tabs must be punched at the factory
to accommodate the bushings.
Self-Regulating – refers to a type of heat trace cable, which has
a decreased wattage output for increasing temperature.
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.
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).
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
Serial Communications – A method of transmitting data between devices.
Set Point – control setting to achieve or maintain temperature.
Screw Plug Immersion Heaters – immersion heaters, which mount with
a screw plug, typically with a standard NPT thread. Most have an available selection
of terminal housings for various environments. Some also include built-in mechanical
thermostats.
Shape Factor – in radiant applications, the amount of energy received
by the target relative to heater rating and distance to the target.
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 Length – the length of the sheath measured without the terminals
or protruding terminal pins. Typically held within one percent for Chromalox tubular
heaters.
Shield – material surrounding a conductor(s) to prevent interference
of electrostatic or EMI from external sources.
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.
Single End Tubular Heaters – tubular heaters with both electrical
connections located at one end of heater. Simplifies wiring.
Slide Wire Feedback – A potentiometer that varies resistance in
response to a valve position. This provides valve position information to the valve
controller.
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 Metal Melting Pot – an open top vessel designed to melt solder,
tin and/or lead.
Soft Start – reduces voltage on initial start-up which reduces
power to the heaters.
Solid State Relay – a solid state switching device which completes
or breaks a circuit electrically with no moving parts.
Span – the difference between the upper and lower limits of a controller’s
range.
Specific Gravity – the ratio of mass of any material to the same
volume of pure water at 4°C.
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.
Spring Loaded – refers to sensor probes designed for use in thermowells.
The probe has a spring, which forces the tip of the sensor to make good contact
with the inside end of a properly chosen thermowell.
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.
Steam Boilers – automatically provide a source of steam for processes
or other uses. Boilers are available in a wide variety of sizes and styles. Accessories
include automatic blowdown, condensate return systems, steam separators and more
Strip Heaters – heating elements with a rectangular cross section,
usually used to heat objects by clamp on conduction or heating air by free or forced
convection.
Super Heating – the heating of a liquid above its boiling temperature
without changing to a gaseous state; or the heating of a gas considerably above
the boiling temperature.
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.
T
Temperature Gradient – the range of temperature variations at various
physical locations throughout a thermal system.
Tera – the prefix for one trillion(T).
Terminal Pin – a pin in the end of tubular and similarly constructed
heaters to which the resistance winding is attached. The pin extends out of the
heater and is attached to a terminal to facilitate wiring.
Terminals – the means to attach wiring to heaters. For tubular
heaters, a wide variety are available to accommodate wires, lugs, or 1/4 inch push
on connectors.
Thermal Conductivity – the property of a material to conduct heat.
Thermal Expansion – an increase in size due to an increase in temperature.
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 probe manufactured of a mixture
of metal oxides then encapsulated in epoxy or glass. A large change in resistance
is exhibited proportional to a change in temperature. The resistance usually decreases
as temperature rises.
Thermocouple – a temperature sensing probe consisting of the junction
of two dissimilar metals which has a millivolt output proportional to the difference
in temperature between the “hot” junction and the lead wires (cold junction).
Thermowell – a closed-end tube into which a temperature sensor
is inserted to isolate it from the environment.
Thin Blade Heaters – tubular type heaters having a 1 / 4/ by 1
inch cross section. Available in single or three phase models
Touch Safe Design – optional shields available on some SCR power
control modules, reduce the possibility of personnel coming in contact with high
voltage.
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.
Transmitter – a device used to transmit temperature data from the
sensor.
Tubular Element – cylindrical component heating element made with
a metal sheath, enclosing a magnesium oxide surrounded Nichrome resistance winding.
Cross section may be round, heart shape or flat pressed.
U
Undershoot – excursion of temperature below set point.
Underwriters’ Laboratories (UL) – a third party approval agency
for components and finished products.
Ungrounded Junction – A thermocouple junction fully insulated from
the sheath.
User Selected Security Code – a feature on some PID controls, allows
the selection of an unique code, if the default codes are compromised.
V
VDE – an independent, German third party testing organization for
product safety. Viscosity – the inherent resistance of a substance
to flow Voltage – an electrical potential, which is measured in
volts.
W
Wattage – a unit of measurement of electrical power. In a resistive
circuit, VI = W (See Ohms Law formulas).
Watt Density – the rated wattage of an element per unit of surface
area. Usually expressed in watts per square inch.
Welded – one common method of attaching sensor probe to threaded
hub. Welding produces a moisture proof, mechanically strong bond.
Z
Zero Voltage (or Zero Crossover) Switching – completing or breaking
of a circuit when the voltage wave form crosses zero voltage.
