What is a temperature controller?
Are there different types of temperature controllers?
The definitions utilized in our industry are numerous. What is critical to Oven Industries and to you our customer is how these definitions relate to temperature control and temperature sensing.
AC Line Frequency – The frequency of the alternating current power line measured in Hertz (Hz), usually 50, 60 and 400 60 Hz.
AC/DC – Both alternating current and direct current.
Alarm – A signal that indicates that the process has exceeded or fallen below the set point or limit point. For example, an alarm may indicate that a process is too hot or too cold. Most Oven Industries temperature controllers have an alarm that you can enable or disable.
Alternating Current (~) - An electric current that reverses at regular intervals and alternates positive and negative values.
American Wire Gauge (AWG) – A standard of the dimensional characteristics of wire used to conduct electrical current or signals. AWG is identical to the Brown and Sharpe (B & S) wire gauge. Oven Industries can provide you with information for the input and output connections use by our temperature controller and the wire awg of our temperature sensors.
Ammeter – An instrument that measures the magnitude of an electric current.
Ampere (amp. A) – A unit that defines the rate of flow of electricity (current) in a circuit.
Analog – A method of representing data using the amplitude of a signal. A true analog signal has infinite resolution .
Automatic Power Reset – A feature in latching controllers that does not recognize power outage as a limit condition. When power is restored, the output is re-energized automatically, as long as the temperature is within limits.
Auto-Tune – A feature that automatically sets temperature control PID values to match a particular thermal system. (Bill has talked about doing this feature but we don’t have this option)
Bandwidth – A symmetrical region above and below the set point in which proportional control occurs.
Celsius © – Also known as Centigrade. A temperature scale in which water freezes at 0ºC and boils at 100ºC at standard atmospheric pressure.
Closed Loop – A control system that uses a temperature sensor to measure a process variable and makes decisions based on that input.
Control Mode – The type of action that a temperature controller uses. For example, on-off, time proportioning, PID, or manual, and combinations of these.
Current – The rate of flow of electricity. The unit of measure is the ampere (A).
Current Transformer – A transformer designed for measuring electrical current without breaking the circuit to connect a meter.
Data Logging – A method of recording a process variable over a period of time. Used to review process performance.
DC Direct Current – An electrical current that flows in one direction.
Dead Band – The range through which a variation of the input produces no noticeable change in the output. In the dead band, specific conditions can be placed on control output actions.
Derivative Control (D) – The last term in the PID control algorithm. Action that anticipates the rate of change of the process variable and compensates to minimize overshoot and undershoot. Derivative control is an instantaneous change of the control output in the same directions as the proportional error. This is caused by a change in the process variable (PV) that decreases over the time of the derivative (TD). The TD is in units of seconds.
Deviation – Any departure from a desired value or expected value or pattern. Sometimes referred to as delta.
Dielectric – An insulating material with very low electrical conductivity.
Dielectric Strength – The potential gradient at which electric failure or breakdown occurs. Also known as breakdown potential.
Differential Control – A control algorithm where the set point represents a desired difference between two processes. The temperature controller then manipulates the second process to hold it at a set value relative to the first controller.
Display Capability – In an instrument with digital display, the entire possible span of a particular parameter such as set temperature Oven Industries has several temperature controls that have digital displays.
Droop – In proportional controllers, the difference between set point and actual value after the system stabilizes. The integral (reset) component of PID control corrects droop.
Dual Element Sensor – A sensor with two independent sensing elements. Usually used to measure temperature gradients or provide redundancy in a single point sensor assembly.
Earth Ground – A metal rod, usually copper, that provides an electrical path to the each, to prevent or reduce the risk of electric shock.
EIA/TIA-232 (formerly RS-232) – An Electronics Industries of America (EIA)/Telecommunication Industry Association (TIA) standard for interface between data terminal equipment and data communications equipment for serial binary data interchange. This is usually for communications over a short distance (50 feet or less) and to a single device.
EIA/TIA-485 (formerly RS-485) – An Electronics Industries of America (EIA)/Telecommunication Industry Association (TIA) standard for electrical characteristics of generators and receivers for use in balanced digital multipoint systems. This is usually used to communicate with multiple devices over a common cable or where distances over 50 feet are required.
Electromagnetic Compatibility (EMC) – The ability of equipment or a system to function as designed in its electromagnetic environment without introducing intolerable electromagnetic disturbances to that environment or being affected by electromagnetic disturbances in it.
Electromagnetic Interference (EMI) – Electrical and magnetic noise imposed on a system. There are many possible causes, such as switching ac power on inside the sine wave. EMI can interfere with the operation of controls and other devices.
Electromechanical Relay – A power switching device that completes or interrupts a circuit by physically opening or closing electrical contacts. These are mechanical devices which have a rated life. Not recommended for PID control.
Electrostatic Discharge (ESD) – An electrical discharge (static electricity), usually of high voltage and low current. For example, the shock that occurs when walking across a carpet.
Endothermic – A process that absorbs heat.
EPROM – Erasable, programmable, read-only memory inside the controller.
Ethernet – A local area network (LAN) protocol that supports a bus or star-configured network with speeds up to 1,000 mbps (megabits per second).
Exothermic – A process that releases heat.
Fahrenheit – The temperature scale that sets the freezing point of water at 32ºF and its boiling point at 212ºF at standard atmospheric pressure. The formula for conversion to Celsius is:
ºC = 5/9 (ºF – 32ºF).
Ferrule – A tubular compression component used to mount a temperature sensing probe. It creates a gas-tight seal.
Firmware – A combination of software and hardware, where the software is written (embedded) into a ROM (read only memory) chip, such as PROM (programmable read only memory) or EPROM (erasable programmable read only memory).
Freezing Point – The fixed temperature point at which a material changes from a liquid to a solid state. This is the same as the melting point for pure materials. For example, the freezing point of water is 0ºC or 32ºF.
Frequency – The number of cycles over a specified period of time usually measured in cycles per second. Also referred to as Hertz (HZ). The reciprocal is called the period.
Fuse – A device that protects electric circuits by interrupting power in a circuit when an overload occurs. Traces require special, fast acting fuses, sometimes referred to as (amps²-seconds) fuses.
Fuzzy Logic – A type of artificial intelligence logic that uses a percentage match to represent variable or inexact data, rather than the exactly true (1) or false (0) of binary logic.
Safety Ground – An electrical line with the same electrical potential as the surrounding earth. Electrical systems are usually grounded to protect people and equipment from shocks due to malfunctions. ( our customer drawings talk about ground but it is circuit ground not safety ground)
GUI Graphic User Interface – A representation, on a computer screen, of a system or process that allows the computer user to interact with the system or process.
Heat – Energy transferred between material bodies as a result of a temperature difference between them.
Heat Transfer – The flow of heat energy from one body of higher temperature to one of lower temperature.
Heat Sink – Any object that conducts and dissipates heat away from an object in contact with it. This can be finned piece of metal, usually aluminum that is used to dissipate heat generated by electrical and electronic devices.
Hertz (Hz) – Frequency, measured in cycles per second.
Hi-Pot Test – A test that applies a high voltage to a conductor to assure the integrity of the surrounding insulation.(when we hi-pot it checks for a breakdown for the chassis to the circuit)
Hysteresis – A change in the process variable required to re-energize the control or alarm output. Sometimes called switching differential.
Impedance (Z) – The total opposition of a circuit to the flow of alternating current. It includes resistance and reactance, and is measured in ohms.
Input – Process variable information that is supplied to the temperature controller
Input Type – The signal type that is connected to an input, such as thermocouple, thermistor, RTD, linear or process.
Sensor Isolation – Electrical separation of sensor from high-voltage circuitry. Allows use of grounded or ungrounded sensing element.
Kelvin (k) – An absolute temperature scale. Zero Kelvin is absolute zero. No degree symbol (º) is used with the Kelvin scale. (0º C = 273.15K, 100ºC = 373.15K).
Kilowatt (kW) – Unit of electrical power equal to 1,000 watts This is calculated by volts X amps
Kilowatt Hour (kWh) – Unit of electrical energy, or work, expended by one kilowatt in one hour. Also expressed as 1,000 watt hours.
kVA – Kilovoltampere or 1,000 volt-amperes (VA). One unit of apparent power equals 1VA.
i-value – The measure of a material’s thermal conductivity coefficient or its ability to conduct heat. Copper conducts better than plastic; copper has a higher k value. The k-value is expressed in W/cmK (watt per centimeter Kelvin) or in Btu/hft.F (Btu per hour per ft. degree Fahrenheit). The k-value is the reciprocal of the R-value, thermal resistance.
Light Emitting Diode (LED) – A solid-state electronic device that glows when electric current passes through it.
Limit or Limit Controller – A highly reliable, discrete safety device (redundant to the primary controller) that monitors and limits the temperature of the process, or a point in the process.
Liquid Crystal Display (LCD) – A type of digital display made of a material that changes reflectance or transmittance when an electrical field is applied to it.
Load – The electrical demand of a process, expressed in power (watts), current (amps) or resistance (ohms). The item or substance that is to be heated or cooled.
Megawatt (MW) – 1x 106 watts or 1,000,000 (one million) watts.
Melting Point – The temperature at which a substance changes from a solid to liquid state. This is the same as the freezing point of pure materials.
Milliampere (mA) – One 10-³ (thousandth) an ampere.
Millivolt (mV) – One 10-³ (thousandth) of a volt.
Minimum Load Current – The smallest load current required to ensure proper operation of an output switching device.
Moisture Resistance – The relative ability to resist permeation by water.
Negative Temperature Coefficient (NTC)– A decrease in electrical resistance that occurs with a temperature increase.
NEMA 4X – A NEMA specification for determining resistance to moisture infiltration and corrosion resistance. This rating certifies the controller as washable and corrosion resistant.
Noise – Unwanted electrical signals that usually produce signal interference most command in sensors but can interfere in temperature controllers Noise Suppression – The use of components to reduce electrical interference that is caused by making or breaking electrical contact, or by inductors.
Offset – Synonym for “droop”. In a stable thermal system, the difference between the process set point and the process actual temperature. An offset variable can be introduced intentionally into the system by some controllers to compensate for sensor placement. In PID control, integral (reset) will eliminate droop. Most Oven Industries temperature controllers that have a communication port have this option
Offstate impedance – The minimum electrical resistance of the output device in the off or de-energized state. It is based on the frequency of the load supply current plus internal and/or external noise suppression devices.
OHM (Ω) – The unit of electric resistance. The resistance value through which one volt will maintain a current of one ampere. See Ohm’s Law.
Ohm’s Law – Current in a circuit is directly proportional to the voltage and inversely proportional to resistance; stated as: E = IR, I = E/R, R = E/I, P = EI where 1 = current in amperes, E- EMF in volts, R = resistance in ohms and P = power in watts.
On-Off Controller – A temperature controller that operates in either full-on or full-off state.
Output – The control signal that affects the end process value. This is what drives you load
Output Type – The form of PID control output, such as time proportioning, distributed zero crossing, serial digital-to-analog converter or analog. Also the description of the electrical hardware that makes up the output. (I think we should talk about types of output. With AC we can talk about zero crossing proportional . DC we can talk about pulse width modulating (PWM)
Parallel Circuit – A circuit configuration in which the same voltage is applied to all components, with current divided among the components according to their respective resistances or impedances.
PD Control – Proportioning control with derivative (rate) action.
Peltier Effect – . A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect)
Percent Power Control – Open-loop control with output power set at a particular level or percent power.
Phase – The time-based relationship between alternating current cycles and a fixed reference point. In electricity, it is usually expressed in angular degrees, with a complete cycle equal to 360º. It describes the relationships of voltage and current of two or more alternating waveforms.
PI Control – Proportioning control with integral (automatic reset) action.
PID – Proportional, Integral, and Derivative – A control mode with three functions: proportional action dampens the system response, integral corrects for droop, and derivative prevents overshoot and undershoot.
Polarity – The electrical quality of having two opposite poles, one positive and one negative. Polarity determines the direction in which a current tends to flow.
Positive Temperature Coefficient (PTC) – An increase in resistance that occurs with an increase in temperature.
Potting – The sealing of components and associated conductors with a compound to exclude moisture and contaminants.
Probe – A temperature sensor. A probe may contain a thermocouple, RTD, thermistor or integrated circuit (IC) sensor. Oven Industries has a wide range of temperature sensors probes in different mechanical packages
Process Variable – The parameter that is controlled or measured. Typical examples are temperature, relative humidity, pressure, flow, fluid level, events, etc. The high process variable is the highest value of the process range, expressed in engineering units. The low process variable is the lowest value of the process range.
Proportional – Output effort proportional to the error from set point. For example, if the proportional bank is 20º and the process is 10º below set point, the heat proportioned effort is 50 percent. The lower the PB value, the higher the gain.
Proportional Control – A control using only the P (proportional) value of PID control.
Radio Frequency Interference (RFI) – Electromagnetic waves between the frequencies of 10 kHz and 300 GHz that can affect susceptible systems by conduction through sensor or power input lines, and by radiation through space.
Ramp – A programmed increase or decrease in the temperature of a set point system.
Reset – Control action that automatically eliminates offset, or droop, between set point and actual process temperature.
Resistance – Opposition to the flow of electric current, measured in ohms.
Resistance Temperature Characteristic – The characteristic change in a sensor’s resistance when exposed to a change in temperature.
Resistance Temperature Detector (RTD) – A sensor that uses the resistance temperature characteristic to measure temperature. There are two basic types of RTDs: the wire RTD, which is usually made of platinum, and the thermistor, which is made of a semiconductor material. The wire RTD is a positive temperature coefficient sensor only, while the thermistor can have either a negative or positive temperature coefficient.
Resistive Loads – All loads that limit the flow of electric current. With pure resistive loads, voltage and current are in phase.
Resolution – An expression of the smallest input change unit detectable for a system output change.
Response Time (time constant) – 1) the time required by a sensor to reach 63.2 percent of a temperature step change under a specified set of conditions. Five time constants are required for the sensor to stabilize at 100 percent of the step change value. 2) With infrared temperature sensing, the time required for a sensor to reach 95 percent of a step change. This is known as the time constant times three. The overall system response time is the sum of the time constants of each component
Semiconductor – Any material that exhibits a degree of electrical conductivity that falls between that of conductors and dielectrics.
Series Circuit – A circuit configuration in which a single current path is arranged among all components.
Set Point – The desired value programmed into a controller. For example, the temperature at which a system is to be maintained.
Shield – A metallic foil or braided wire layer surrounding conductors that is designed to prevent electrostatic or electromagnetic interference from external sources.
Signal – Any electrical transmittance that conveys information.
Soaking – In heat treating or cold treating, the practice of immersing an object.
Soft Start – A method of gradually increase the output power over a period of several seconds. Soft starts are used for heaters that have a low electrical resistance when they are cold, or for limiting in-rush current to inductive loads.
Solid-State Replay (SSR) – A switching device with no moving parts that completes or interrupts a circuit electrically.
Surge Current – A short duration rush of current that occur when power is first applied to capacitive, inductive or temperature dependent resistive loads, such as tungsten or silicon carbide heating elements. It also occurs when inductive loads are de-energized. Surge currents usually last no more than several cycles.
Switch – 1) A device, either electrical or mechanical, used to open or close an electrical current. 2) A computer programming technique that will change a selection from one state to another. 3) A telephone interface that connects callers. 4) A network routing device that provides numbered codes(these are not all relevant to temp control)
Temperature Calibration Point – A temperature at which the output of a sensor is compared against a standard.
Temperature Ambient – The temperature of the air or other medium that surrounds the components of a thermal system.
Thermal Conductivity – The quantity of heat transmitted by conduction through a body per unit area, per unit time, per unit thickness for a temperature difference of 1 Kelvin. This value changes with temperature in most materials and must be evaluated for conditions given. Expressed in Btu/hr-ºF or Watts/meter-ºC.
Thermal Fuse – safety cutoff component opens when predetermined temperature is met
Thermistor – A temperature sensing device made of a semiconductor material that exhibits a large change in resistance for a small change in temperature. Thermistors usually have negative temperature coefficients, although they are also available with positive temperature coefficients.
Thermocouple (T/C) – A temperature sensing device made by joining two dissimilar metals. This junction produces an electrical voltage in proportion to the difference in temperature between the hot junction (sensing junction) and the lead wire connection to the instrument (cold junction).
Time Proportioning Control – A method of controlling power by varying the on-off duty cycle of an output. This variance is proportional to the difference between the set point and the actual process temperature.
Transducer – A device that receives energy in one form and retransmits it in another form. For example, a thermocouple transforms heat energy input into a voltage output.
Transmitter – A device that transmits temperature data from either a thermocouple or a resistance temperature detector (RTD) by way of a two-wire loop. The loop has an external power supply. The transmitter acts as a variable resistor with respect to its input signal. Transmitters are desirable when long lead or extension wires product unacceptable signal degradation.
Triac – A solid-state device that switches alternating current.
Volt Amperes (VA) – A measurement of apparent power. The product of voltage and current is a reactive circuit. VI = VA, where V is volts and I is current in amperes. The term watt is used for real power.
Voltage (V) – The difference in electrical potential between two points in a circuit. It’s the push or pressure behind current flow through a circuit. One volt (V) is the difference in potential required to move one coulomb of charge between two points in a circuit, consuming one joule of energy. In other words, one volt (V) is equal to one ampere of current (I) flowing through one ohm of resistance (R). Or V = IR
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