Scott Process

Equipment Corp

Glossary – Engineering & Process Equipment

Scott4U Gossary of Terms 

Engineering  | Process Equipment  |  Processing 

This is not s complete list of engineering and processing terms but we hope you find this glossary helpful.  

Absolute Zero – Absolute zero is the zero point on the Kelvine and Rankine scale. (-273.15°C or-459.67°F)

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

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 cycles per second (Hz)

Ambient (Temperature) – The temperature of the immediate surroundings in which equipment is to operate

Ambient Compensation – The ability of an instrument to compensate for changes in the ambient so that the changes do not affect control accuracy

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

ANSI – American National Standards Institute

Anti-Foam Additive – Causes air bubbles to break on the surface, prevents build up of foam. Can also help prevent oxidation. They cannot prevent air entrainment, but function as an aid to quicker release of entrained air.

Anti-Oxidant (oxidation inhibitor) – An additive to retard oxidation.

Anti-Rust or Anti-Corrosion Additive – Helps prevent oxidation of metal by displacing water from metal surfaces. It plates to metal with a polarized effect to give an internal “umbrella”, helping to resist iron-oxide formation.

ASME – American Society of Mechanical Engineers

ASTM – American Society for Testing and Materials; an agency that standardizes testing petroleum products.

Atmospheric Pressure (Standard) – Pressure exerted by the earth’s atmosphere. Measured at 60°F (15°C), at sea level, standard atmospheric pressure is 14.7 psia (pounds per square inch atmospheric)

Auto Ignition – Minimum temperature which a substance must be heated without application of flame or spark to cause substance to ignite.

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

AWG (American Wire Gauge) – Refers to the diameter of both power and control circuits wires. The larger the gauge number, the smaller the wire diameter

Bandwidth – The total temperature variation measured at some point in the system, normally the process

Blown film coolers – An in-line cooling coil located in duct work to cool hot blown film

Boiling Point – The boiling point of water (100°C or 212°F at sea level), the temperature at which a substance in the liquid state transforms to the gaseous state

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

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 Fittings – Threaded fittings used to mount or allow a connection through the wall of a tank or casing

Burst Firing – A fast cycling control output, typically 3-32VDC, used in conjunction with a solid state relay

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

Catalyst – A material which promotes some chemical action without itself entering into the reaction.

Cavitation – In a heat transfer system, failure of the material to flow to the suction of the system pump for any reason.

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

Centipoise and Centistoke – A centipoise is 1/100th of the unit of absolute viscosity (the poise), e.g., the viscosity of water at 20C is approximately one centipoise. The centipoise is derived from one kinematic unit of viscosity (the centistoke), by multiplying the latter by the density of the liquid, i.e., 1 centipoise = 1 centistoke x the density of the liquid. These units are part of the metric system, commonly used in Europe and becoming adopted in the U.S. and Canada.

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

Chiller stall – Interruption in the flow of refrigerant through a compressor

Chiller, air cooled – Configuration of refrigeration components where heat is rejected to the surrounding air utilizing a fan to blow air over a condenser coil.

Chiller, Split: – Some portion of the chiller system being remote mounted such as an air-cooled condenser where weight or space are a concern.

Chiller, water cooled – Configuration of refrigeration components installed where heat is rejected utilizing a water to water heat exchanger.

Circuit – A complete or partial path over which current may flow.

Circulating liquid temperature control systems (Temperature control unit)

An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

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

Compression Fittings – Bulkhead fittings designed to allow objects to be mounted through the wall of a tank, etc.

Compressor – Increases the pressure on a substance

Condenser – Converts a substance from a gas into its liquid form, extracting heat from the substance

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

Continuity Check – A test that determines whether current can flow throughout the length of a circuit

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.

Control Loop – The basic control loop of any automatic control system consists of: variable (process); sensor; error detector (of control); control; control element (relay, SSR, SCR); and 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 mode

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

Cooling Tower – Heat removal device used to transfer process waste heat to the atmosphere through the evaporation of water or air to cool the working fluid.

Corrosion Inhibitor – An additive used to retard the corrosion process.

CPS (Hertz) – Cycles per Second

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.

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 – Typically 4-20 milliamp current output which provides a current proportional to the amount of control required

Current Transformer – A transformer designed to accommodate an electrical conductor, and provide a reduced, but linear output at a lower current, for instrument use

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

Default Parameters – The programming instructions permanently written in the software

Definite Purpose Magnetic Contactor – Similar to a motor starter relay, used with on-off controllers for slow processes

Density – Mass per unit of volume, such as lbs/cubic ft

Deposits – Oil-insoluble materials that result from oxidation of the oil and contamination from external sources and settle out in system components as sludge and varnish.

Derivative (Rate) – A control function that measures the rate of increase or decrease of the system temperature and prevents an overshoot condition at initial heat-up and with system disturbances

Deviation – The difference between the selected value and the actual value

Deviation Alarm – An offset value that follows the set point where if Deviation Alarm value is +20°F and the set point is 250°F, then the Deviation Value alarm would be 270°F

Deviation Meter – The display of process temperature on meter that indicates difference of or deviation of the process temperature from the set point

Dielectric Strength – An amount of voltage that an insulating material can withstand before an electrical breakdown occurs

Differential – The temperature difference expressed in degrees between where the control switches off and on

Differential (Dead Band) – is the difference in degrees between temperature control on and off. Also applies to over temperature controls

Differential (Dead Band) – is the difference in degrees between temperature control on and off. Also applies to over temperature controls

Digital Indication – The actual process temperature in indicated by LED or LCD display

Digital Set Point – The desired temperature value is set by an operator

DIN – Deutsche Industrial Norms, a German agency that sets engineering standards

Direct Current (DC) – An electric current flowing in one direction

Disconnect – A main power switch, which provides a means to turn off power before opening a door for servicing. Most disconnects do not provide over current protection that must be provided upstream using fuses or circuit breakers

Display Accuracy – The amount of potential error between a measured value and the control’s displayed value

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

Dual circuit chillers – Multiple compressors used to improve chiller efficiency under varying load conditions

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

Dwell – A time entered into a program during which the set point (SP) remains constant.

Efficiency (control) – The amount of useful output versus energy input, expressed as a percentage

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

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 – When a process 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

Evaporator – Adds heat to a substance, changing it from a liquid to a gas Exothermic – when a process generates heat

Event – A programmable On/Off output used to signal peripheral equipment or a process

Explosion Proof 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 the same type (cannot be mixed). RTD wire may be copper.

Fahrenheit – A temperature scale with 32°F defined as the ice point and 212°F as the boiling point of water at sea level

Fire Point – The temperature at which the fluid will sustain a fire if ignited by an outside ignition source. It is quite common for heat transfer systems to be operated at temperatures above the fire point of the fluid as ignition sources should always be far removed from any heat transfer system.

Flash Point – The temperature at which the vapors produced from a fluid will ignite (flash off) with the presence of an ignition source (the fluid will not burn at this point). The flash point is important from the viewpoint of safety; however, it is quite common for heat transfer systems to be operated at temperatures above the flash point of the fluid.

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 condition

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 – A method 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

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

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.

Header (manifold) – A pipe or tube collects or separates flow from 1 pipe to multiple pipes or vice versa

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 – Typically metal tubes or coils designed to heat or cool solutions, 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

Heat Sink – In power control, typically aluminum plates or ?ns 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 – Conduction: the transfer of heat from one particle of matter to another; Convection: the transfer of heat from one part of a particle to another by the mixing of the warmer particles with the cooler; and Radiant: the transfer of heat from one body to another as the result of the bodies emitting and absorbing radiation energy.

Heat transfer Fluid System – Consist of forced circulation using a pump, heater(s), control panel and related safeties, ready to connect to a process

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 forced circulation using a pump, heater(s), control panel and related safeties, ready to connect to a process

Hertz – Units of expression for frequency, measured in cycles per second

High Temperature Wire – Special wire with high temperature insulation and nickel. Can withstand higher temperatures than plastic insulated copper conductor wire used for general connections. 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

Hot oil temperature control units – Consist of forced circulation using a pump, heater(s), control panel and related safeties, ready to connect to a process

Hydrocarbons – Compounds containing only carbon and hydrogen. Petroleum fluids consist chiefly of hydrocarbons.

Hydrophilic – Having an affinity for water, capable of uniting with or dissolving in water.

Hydrophobic – Having antagonism for water; not capable of uniting or mixing with water.

Hysteresis – The temperature sensitivity designed into the on/off control action between the on and off switching points. Expressed in percentage of control range.

Ice Point – The temperature where pure water freezes (0°C or 32°F)

Immersion Heaters – Electric 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, 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.

Inhibitor – A substance that slows or prevents chemical reactions, such as oxidation or corrosion.

Insulation Resistance – Is the resistance of an insulator to current flow from a conductor to ground 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

Isothermal – A process or area that maintains a constant temperature

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.

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) – 1,000 watts or 3,412 Btu per hour

Kilowatt Hour – Electrical unit of energy expended by one kilowatt in one hour

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.

Liquid Level Control – Detects liquid level below a reference depth and can be used for replenishment

Load – The electrical demand of a process expressed as wattage, amps or resistance (ohms)

Manifold (header) – A pipe or tube collects or separates flow from 1 pipe to multiple pipes or vice versa

Manual Reset – The adjustment on a proportional control which shifts the proportioning band in relation to the set point to eliminate droop or offset error

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

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 contain mercury, a hazardous substance, not permitted in some plants.

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

Moisture Resistant Housing – A terminal housing designed to meet the requirements of NEMA 4.

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 (control) – 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

NPS/NPSM (National Pipe Straight Thread) – A straight not tapered thread that meets ANSI/ASME standards

NPT (National Pipe Thread) – A tapered thread that meets ANSI/ASME standards in the USA

Offset – The difference in temperature between the set point and the actual process temperature

OHM – The unit of electric resistance

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. 40%), in the event of an open sensor

OSHA – Occupational Safety and Health Administration (or Agency) is a US Government agency that specifies and enforces safety in the workplace

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

Overshoot – Excursion of temperature above the set point

Oxidation – The process of combining with oxygen. All petroleum products are subject to oxidation to some degree. The reaction increases with rise in temperature. Oxidation produces oil-insoluble oxidized materials, which result in viscosity increase and deposits.

Oxidation Inhibitor – A chemical additive that minimizes the formation of harmful acids and varnish forming compounds that form when a fluid is subjected to air at elevated temperatures.

Oxidation Stability – The resistance of lubricants to chemically react with oxygen. The absorption and reaction of oxygen may lead to deterioration of lubricants.

Oxidative Degradation – Oxidative degradation is the reaction of oxygen (in air) with the fluid by a free radical mechanism to form larger molecules which end up as polymers or solids. These thicken the fluid and increase its viscosity. A more viscous fluid will be more difficult to pump, have poorer heat transfer characteristics as well as an increased chance of coke formation. Oxidation is also accompanied by an increase in the acidity (TAN) of the fluid. As with all chemical reactions, oxidation occurs more rapidly as the temperature is increased. At room temperature, the reaction rate is hardly measurable. However, it can become a factor in the life of the fluid in certain styles of heat transfer systems. At temperatures encountered in systems in use in the plastics extrusion and die casting industries, as an example, oxidation is the main cause of fluid degradation.

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 ?ring mode in which the SCR’s are turned on for a portion of each half cycle. Necessary for high inrush and/or inductive loads

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); and derivative (rate)

Polarity – Having two oppositely charged poles: one positive, one negative

Pour Point – The lowest temperature at which a liquid will pour under specified conditions.

Pour-Point Suppressants – Prevent insoluble wax molecules in oil from building a honeycomb (lattice-like structure) at colder temperatures. Particularly useful for parafiinic oils. Gives useful ability to pour at lower temperatures.

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 Value – The indicated value of the parameter being measured/controlled

Process Variable – The parameter being controlled or measured such as temperature, flow, level, pressure, etc

Programmable Controller – The ability of controller to vary the process temperature (PV) by changing the set point (SP) as a function of time. The controller varies the process according to the selected program. The program is stored as a series of segments. See also Ramp, Dwell, and Step

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.

Protocol, Ethernet Modbus – Common transportation protocol for the Internet and is the defacto standard of corporate enterprise systems. Ethernet is a hardwire, typically category 5e cable with RJ45 connectors Hub port.

Protocol, LAN – Network layer protocols that are responsible for exchanging information between routers so that the routers can select the proper path for network traffic of communication.

Protocol, Modbus – A defined digital communication network that has one master and one or more slave devices. The Modbus protocol defines an orderly exchange of information from the master device to slave devices. Other devices are: DeviceNet, ControlNet, EtherNet, Profibus

Protocol, SPI – Society Plastics International digital communications protocol (RS-485 driven).

Psia – pounds per square inch absolute. Pressure reference to a vacuum

Psig – pound per square inch gauge. Pressure reference to ambient air pressure

Pump Tank – A metal or non-metallic chiller system water tank with a weir to separate hot return water and cooled supply water

Ramp – A programmed rise in temperature

Range (control) – An area between two limits in which a control action takes place, 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 set point – The signal sent from the customers host control to the Mokon controller which will adjust the working setpoint (SP) temperature.

Remote Set point and Retransmission – Analog communications allowing the controller to send and receive process variable information, most common available signal types are 0-10 vDC and 4-20 mA.

Remote Shutdown – A feature 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 – 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.

Retransmission – The signal that is sent back from the Mokon controller to the customers host control and is a representation of the working process variable temperature (PV).

Retransmit Output – Analog output scaled to the process or the set point value

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.

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

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 Breakdown Protection – circuitry which ensures safe process shut down in the event of sensor failure

Sensor Selection – A menu or hardware feature on controls which allows selection of a number of thermocouple types, RTD’s and /or other sensors

Serial Communication – Digital communication allowing one or more instruments to be connected using a 2 or 4 wire connection. The communication is done using a protocol.

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).

Set Point – Control setting to achieve or maintain temperature

Set Point Accuracy – The potential error between a measured value and the control setting

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 circuit chillers – Single compressor used to reject heat from a industrial process

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 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 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

Specific Gravity – The ratio of mass of any material to the same volume of pure water at 4°C

Stability (control) – 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

Step – The set point (SP) changes instantaneously from one value to a new value.

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

TAN (Total Acid Number) – Acids are formed when a fluid comes in contact with oxygen, TAN levels are a means to show the extent of which a fluid has been oxidized. New fluids typically have a TAN less than 0.05, most fluids should be changed at and have a condemning limit of a TAN of 1.0. The rate of oxidation is minimal under 200F, however, as the temperature climbs the effects of oxidation are exponential. It is an industry accepted standard to assume the rate of oxidation doubles for each 15 degree increase above 200F.

TCU (Temperature Control Unit) – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Temperature control systems – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Temperature control unit (TCU) – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Temperature controllers – An electrical/electronic control or an assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Temperature Gradient – The range of temperature variations at various physical locations throughout a thermal system

Terminals – The means to attach wiring to heaters etc to accommodate wires, lugs, or push on connectors

Thermal Conductivity – The property of a material to conduct heat

Thermal Degradation – Thermal degradation or thermal cracking is the breaking of carbon – carbon bonds in the fliud molecules by heat to form smaller fragments which are free radicals. The reaction may either stop at that point, in which case smaller molecules than previously existed are formed, or the fragments may react with each other to form polymeric molecules larger than previously existed in the fluid. In heat transfer terminology, the two types of degradation products are known as “low boilers” and “high boilers”. If thermal degradation occurs at extreme temperatures greater than 400C (752F), the effect is not only to break carbon – carbon bonds but to separate hydrogen atoms from carbon atoms and form coke. In this case, fouling of the heat transfer surfaces is very rapid and the system will soon cease to operate. The effect of the low boilers is to decrease the flash point and viscosity of the fluid as well as to increase its vapor pressure. The effect of the high boilers is to increase the viscosity of the fluid as long as they remain in solution. However, once their solubility limit is exceeded, they begin to form solids which can foul the heat transfer surfaces.

Thermal Expansion – An increase in size due to an increase in temperature

Thermal Fluid solutions – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Thermal fluid system – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

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: work or load; heat source; heat transfer medium; and 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 pro-portional to the difference in temperature between the “hot” junction and the lead wires (cold junction).

Thermolators – An old term used to describe a TCU or temperature control system

Thermoregulators – An old term used to describe a TCU or temperature control system

Thermowell – A closed-end tube into which a temperature sensor is inserted to isolate it from the environment

Tonnage – Measurement of a chiller’s ability to cool (a ton of cooling is the amount of cooling provided by the melting of one ton of ice in one day)

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.

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

Variable frequency drive (VFD) – An adjustable-speed drive, often used in centrifugal chillers, which provides energy savings over the traditional constant-speed drive

Viscosity – A measure of a fluids resistance to flow. A higher viscosity is essentially a thicker fluid. It is desirable for most high temperature heat transfer fluids to have viscosity in the range of 20cst to 40cst at 104F. Another aspect of a fluids viscosity is its VI (Viscosity Index) or how a fluids viscosity is affected by temperature. It’s a measure of the rate of change of viscosity with temperature. In lubricants a high VI is desirable to maintain a relatively consistent viscosity throughout the useable temperature range. In heat transfer fluids a lower VI is more desirable in order to allow the fluid to thin out (reduce viscosity) with temperature increases. This allows for more efficient thermal transfer properties.

Voltage – An electrical potential, which is measured in volts

Water temperature control units or systems – An electrical assembly consisting of a pump, motor, electric heater, process and limit controllers, and other safety devices

Watt Density – The rated wattage of an element per unit of surface area, usually expressed in watts per square inch

Wattage – A unit of measurement of electrical power. In a resistive circuit, VI = W (See Ohms Law formulas)

Zero Voltage (or Zero Crossover) Switching – Completing or breaking of a circuit when the voltage wave form crosses zero voltage