| Accuracy |
The difference between the reading of an instrument and the true value of what is being measured, expressed as a percent of full instrument scale. |
| Action |
The function of a controller. Specifically, what is done to regulate the final control element to effect control. Types of action include ON-OFF, proportional, integral and derivative. |
| Active Device |
A device capable of producing gain; for example, transistors, and ICs. |
| Alarm |
A condition, generated by a controller, indicating that the process has exceeded or fallen below the limit point. |
| Ambient Temperature |
The temperature of the immediate surroundings in which a controller must operate. |
| Automatic Tuning |
Sometimes referred to as "self-tuning." The ability of a control to select and adjust the three control parameters (Proportional, Integral, and Derivative) automatically via a complex algorithm. Generally no operator input is required. |
| Closed Loop |
A signal path which includes a forward path, a feedback path and a summing point, and forms a closed circuit. |
| Cold Junction Compensation |
Measurement of temperature at thermocouple connections to controller and compensation for the "cold end" junction millivoltage generated here. |
| Common Mode |
The noise signal that is common to all sensor wires. |
| C/MOS Digital Timing |
An integrated circuit timing control method using a self-contained oscillator, digital counter and output circuit to drive relays or trigger solid state outputs. Characterized by very low power consumption and immunity to voltage fluctuations. CMOS complementary metal-oxide semiconductor. |
| Cycle Time |
The time necessary to complete a full ON-through-OFF period in a time proportioning control system. |
| DV/DT |
Rate of change of voltage over time. |
| Dead Band |
The range through which an input can be varied without initiating observable response. |
| De-Energize |
The removal of power from a circuit or electrical device. |
| Derivative |
The process by which a controller senses the rate of change and alters output. |
| Deviation Alarm |
An alarm referenced at a fixed number of units, plus or minus, from setpoint. |
| Dielectric Strength (AKA Dielectric Withstand) |
The voltage insulation integrity of any part of a timer’s circuitry versus the timer’s metal enclosure and the relay output contact terminals. UL/CSA/VDE Recognized / CE Marked units have a higher dielectric strength because of the more stringent insulation requirements. |
| Digital Circuitry |
Electronic logic circuitry that operates by pulse counting and switching. Very accurate method of controlling timing devices. |
| DIN |
Deutsche Industrial Norms, a widely-recognized German standard for engineering units. |
| Differential |
The temperature difference between the points at which the controller turns the load on and off. Typically used when discussing an on/off controller. |
| Direct Acting |
Increase in value of output as the measured value increases. |
| Drift |
A deviation of the system from setpoint that typically occurs over a long period of time. Drift may be caused by such factors as changes in ambient temperature or line voltage. |
| Droop |
Occurs when the actual system temperature stabilizes at some value below the desired setpoint. If system droop is unacceptable, a common solution is the use of a control incorporating an automatic or manual reset feature. |
| Duty Cycle |
Percentage of load "ON" time relative to total cycle time. |
| Energize |
To apply rated voltage to a circuit or device, such as a coil of a relay, etc., in order to activate it. |
| External / Remote Adjustment |
A timer with a time-adjusting potentiometer separate from the main unit. Two terminals for connecting wires are on the timer. |
| Factory-fixed, Factory set |
A timer that has a fixed time delay built in; not variable. |
| False Transfer |
Sometimes called False Operation or False Output. A momentary closing of the relay output contacts that occurs on certain types of timers if the input voltage is removed before completion of the time delay period. |
| False Triggering |
Premature switching in a timer caused by line voltage transients or brief power interruptions. |
| Feedback Controller |
A mechanism that measures the value of the controlled variable, compares with the desired value and as a result of this comparison, manipulates the controlled system to minimize the size of the error. |
| First Cycle Effect (Error) |
A large additive step to a desired time period which is produced by certain types and designs of timers. Usually observed on the first cycle after an extended rest period. Frequently not mentioned in specifications of repeatability. |
| Fixed Conditions |
Conditions of constant temperature and voltage during which timer repeatability is measured and stated. |
| Frequency Response |
The response of a component, instrument, or control system to input signals at varying frequencies. |
| Form A Contacts |
A term used to describe one set of Normally Open (NO) contacts with a single load. |
| Form B Contacts |
A term used to describe one set of Normally Closed (NC) contacts with a single load. |
| Form C Contacts |
A term used to describe one set of Normally Open (NO) and Normally Closed (NC) contacts with a common load. |
| Gain |
Amount of increase in a signal as it passes through any part of a control system. If a signal gets smaller, it is attenuated. If it gets larger, it is amplified. |
| Guaranteed Soak |
On a ramp and soak controller, a feature that stops the clock if the temperature drops below a preset value, then continues the timing when the temperature recovers. |
| Heat Sinking |
A means of removing heat from a power handling electronic device using finned radiators or metal-to-metal thermal conduction. |
| Hysteresis |
Temperature sensitivity between turn on and turn off points on on-off control. Prevents chattering. |
| I2T |
A measure of maximum one time overcurrent capability for a very short duration. Value used for fuse sizing to protect SCRs. |
| Impedance |
The total opposition to electrical flow in an ac circuit. |
| Inductive Load |
The device that a timer controls which initially resists a change in current; typically a coil, such as a solenoid, contactor or relay. |
| Initiate |
Actuation of the timing sequence. |
| Input Voltage |
Term used to describe the operating voltage of a timer. Can be the same or different than output voltage depending on timer. |
| Input Voltages |
A selection of AC or DC voltages over which a timer can be specified to operate. |
| Inrush |
The initial surge of current that the output of a timer handles when switching certain loads, such as tungsten lamps, motors or capacitive loads. |
| Integral Function |
This automatically adjusts the position of the proportional band to eliminate offset. |
| Isolation |
Electrical separation of sensor from high voltage and output circuitry. Allows for application of grounded or ungrounded sensing element. |
| Lag |
The time delay between the output of a signal and the response of the instrument to which the signal is sent. |
| Latching Alarm |
Requires operator intervention to reset even though the alarm condition on the input may have disappeared. |
| Load |
Any device that is controlled by another. Generally expressed as a current or power requirement, i.e., 10 amp load — 300 watt or volt ampere load. |
| Magnal Base |
An 11-pin tube-type base with an aligning key in the center to insure correct insertion of the base into a socket. Often erroneously called 11-pin octal. |
| Metal Oxide Varistor (MOV) |
A semiconductor device that acts as a safety valve to absorb high voltage transients harmlessly, thereby protecting the SCRs and preventing false firing. |
| Millisecond |
One one thousandth of a second. 1ms, 1/1000 sec., .001 sec. |
| MOSFET |
A transistor made with metal oxide semiconductor technology that can switch large amounts of current with a small control signal. Very reliable and stable in high temperature applications. MOSFET=metal-oxide semiconductor field-effect transistor. |
| Noise |
An unwanted electrical interference. |
| Nominal Voltage |
A single value of voltage falling within an allowable operating range, e.g., 120 volts as opposed to the range of 102 to 138 volts. |
| Normal Mode Rejection |
The ability of an instrument to reject interference; usually of line frequency across the input terminals (AKA common mode). |
| Normally Closed (N.C.) or Form B Contacts |
Relay contacts that are closed when the relay is in a de-energized condition. |
| Normally Open (N.O.) or Form A Contacts |
Relay contacts that are open when the relay is in a de-energized condition. |
| Octal Base |
An 8-pin tube-type base with an aligning key in the center to insure proper insertion of the base into a socket. |
| Offset |
A sustained deviation of the controlled variable from setpoint (this characteristic is inherent in proportional controllers that do not incorporate reset action). Also referred to as Droop. |
| Ohm, K ohm, megohm |
Units of resistance. Ohm is basic unit. Practical units for timing purposes are K ohm (1,000 ohms) and megohm (1,000,000 ohms). |
| On/Off Control |
Control of temperature about a setpoint by turning the output full ON below setpoint and full OFF above setpoint in the heat mode. |
| Onboard Adjustment |
A timer with a means of time adjustment as part of its construction, such as a knob and dial. |
| Open Loop |
Control system with no sensory feedback. |
| Operating Temperature |
The temperature range over which a timer will operate and maintain its specified performance criteria. |
| Operating Voltage |
The voltage range over which a timer will operate and maintain its specified performance criteria. |
| Output |
Action in response to difference between setpoint and process variable. |
| Overshoot |
Condition where temperature exceeds setpoint due to initial power up. |
| Parameter |
A physical property whose value determines the response of an electronic control to given inputs. |
| PD Control |
Proportioning control with rate action. |
| Phase |
The time-based relationship between two alternating waveforms. |
| Phase-angle Firing |
A form of power control where the power supplied to the process is controlled by limiting the phase angle of the line voltage as opposed to burst firing. |
| PI Control |
Proportioning control with auto reset. |
| PID |
Proportional, integral and derivative control action. |
| Polarity Protection |
Also called Reverse Polarity Protection. The protective circuity incorporated in a timer in the event a wrong DC input voltage polarity is applied. |
| Positive Temperature Coefficient |
A characteristic of sensors whose output increases with increasing temperature. |
| Potentiometer, Pot |
A variable resistor controlled by a rotating shaft. On timers it is adjusted by a knob to vary the delay time. |
| Power Leakage |
A term used to describe the current that flows through a solid state output when it is off. |
| Power Requirements |
The maximum power required for operation of a timer at a normal voltage. This is expressed in watts or volt-amperes. |
| Process Variable |
System element to be regulated, such as pressure, temperature, relative humidity, etc. |
| Proportional Action |
Continuously adjusts the manipulated variable to balance the demand. |
| Proportional Band |
The amount of deviation of the controlled variable required to move through the full range (expressed in % of span or degrees of temperature). An expression of Gain of an instrument (the wider the band, the lower the gain). |
| Proportioning Control Plus Derivative Function |
A controller incorporating both proportional and derivative action senses the rate temperature change and adjusts controller output to minimize overshoot. |
| Proportioning Control Plus Integral |
A controller incorporating both proportional and integral action. |
| Proportional, Integral and Derivative Control |
A PID controller is a three-mode controller incorporating proportional, integral, and derivative actions. |
| Quick Connect (QC) Terminals |
Blade type male terminals 3/16" (0.1875") or 1/4" (0.25") in width. On relay bases can be plugged into a socket or individually terminated with matching female connectors. |
| Ramp |
Automatic adjustment for the setpoint for the temperature increase or decrease from process temperature. The target value can be either above or below the current measured value. The ramp value is a combination of time and temperature. |
| Ramp To Setpoint |
Allows the operator to enter a target time for the controller to reach setpoint. |
| Range |
The difference between the maximum and the minimum values of output over which an instrument is designed to operate normally. |
| Rate(Action) |
Control function that produces a corrective signal proportional to the rate at which the controlled variable is changing. Rate action produces a faster corrective action than proportional action alone. Also referred to as Derivative Action. Useful in eliminating overshoot and undershoot. |
| RC Snubber Circuit |
Controls the maximum rate of change of voltage and limits the peak voltage across the switching device. Used to prevent false firing of Thyristors. |
| RC Timing |
A basic timing circuit consisting of a resistor (fixed or variable) in series with a capacitor. When a voltage is applied to the resistor-capacitor circuit, the voltage across the capacitor increases as a function of time. At a determined voltage level a solid state trigger device fires or conducts to energize a relay. |
| Re-cycle Effect |
See First Cycle Effect |
| Re-cycle Time |
The non-timing period of a timer between timing cycles. |
| Relay Output Form |
DPDT: Double Pole, Double Throw. A relay with two separate poles, each with a Normally Closed (N.C) and Normally Open (N.O.) contact. AKA 2FormC. |
| S.P.S.T (N.O.) Contact |
Single Pole, Single Throw N.C., A one pole relay with a single Normally Closed contact AKA 1FormA. |
| S.P.S.T (N.C.) Contact |
Single Pole, Single Throw N.O., A one pole relay with a single Normally Open contact AKA 1FormB. |
| S.P.D.T, Contacts |
Single Pole, Double Throw. A one pole relay with Normally Closed (N.C.) and Normally Open (N.O.) contacts. AKA 1FormC. |
| 3.P.D.T. |
Three Pole, Double Throw. A relay with three separate poles, each having Normally Closed (N.C.) and Normally Open (N.O.) contacts AKA 3FormC. |
| Relay Pull-in Time |
The time required for the timer internal relay to switch from its de-energized position. Specified in milliseconds (msec). |
| Repeat Accuracy |
The maximum variation in a time period, expressed in a ± percentage from the first timing cycle to successive timing cycles. This is within the operating voltage and temperature range. |
| Reset Action |
Control function that produces a corrective signal proportional to the length of time and magnitude the controlled variable has been away from the setpoint. Accommodates load changes. Also called Integral Action. |
| Reset Time |
The length of time that input power must be interrupted or initiate switch must be operated to initiate another cycle in a timer. |
| Reset/Recycle Time |
The minimum period of time in milliseconds required to turn a timer OFF and/or ON again for a new cycle without loss of repeat accuracy. |
| Resistive Load |
The device that the timer controls that has no inductance or capacitance; example is a heating element. 100% power factor. |
| Resistor |
A device that opposes electric current flow, measured in ohms. In timers, used to set charge rates for timing capacitors or frequency in digital oscillators. |
| Reverse (inverse) Acting |
Reduces the output as the measured value increases. |
| Radio Frequency Interference (RFI) |
RFI is commonly generated by devices that switch the output power at some voltage other than zero. Typically, phase-angle fired Thyrstors may generate RFI while zero-cross fired Thyrstors virtually eliminate RFI. |
| Resistance Temperature Detector (RTD) |
Typically a wire wound device that displays a linear change in resistance for a corresponding temperature change. An RTD has a positive temperature coefficient. |
| SCR |
A solid-state semiconductor component that conducts or resists current flow depending upon whether a trigger voltage is present at the gate terminal. |
| Segment |
In a ramp and soak controller, one part of a profile. |
| Sensitivity |
The minimum change in input signal required to produce an output change in the controller. |
| Series Mode |
A condition in which a noise signal appears in series with a sensor signal. setpoint: The position to which the control point setting mechanism is set, which is the same as the desired value of the controlled variable. |
| Soak |
One segment with no setpoint change. |
| Solid State |
A general term for semiconductor electronic circuitry for electriconic devices with no moving parts. |
| Solid-State Relay (SSR) |
Semiconductor device that switches electrical current on and off in response to an electrical signal at the control terminals. |
| Solid State Timer |
A timing device which uses no moving parts to accomplish load switching. |
| Span |
The range between Minimum and Maximum setpoints. |
| Stab / Square Base |
Used in reference to a 0.187" QC Blade Terminal with essentially a square panel. The terminals are often called Blade, Fast-On, QC (Quick Connect), Spade, Tab, etc. It is a flat male terminal 0.187" wide x .02" thick, properly spaced in a panel for plug-in mounting. Pierced holes in the terminals accommodate solder wiring. |
| Standby |
Method of putting controller into the idle mode. |
| Storage Temperature |
The maximum temperatures to which a timer circuit can be exposed in the storage (non-operative) state and thereafter provide reliable performance within the operating temperature range. |
| Surge |
A rapid increase in voltage or current by a power source. Can destroy a timer if not limited. |
| Surge Current |
A high current of short duration that generally occurs when the power is first applied to inductive loads. The surge generally lasts no more than several ac cycles. |
| NTC Thermistor |
A bead-like temperature sensing device consisting of metallic oxides encapsulated in epoxy or glass. The resistance of a NTC (Negative Temperature Coefficient) thermistor typically falls off sharply with increasing temperature, making it a particularly good sensing device. |
| Temperature Range End Limits (Tolerance) |
The minimum and maximum temperature which can not be exceeded during storage or operation in order to assure reliable operation of device. |
| Thermocouple |
The junction of two dissimilar metals. A small voltage is generated at this junction, increasing as its temperature rises. Common types are "J" and "K" Type. |
| Thermocouple Break Protection |
Fail-safe operation that ensures output shutdown upon an open thermocouple condition. |
| Thyristor |
Any of a group of solid-state controlling devices. These devices are referred to as TRIACs, SCRs and DIACs. |
| Timing Ranges |
Time delay periods available for a particular type timer. |
| Timing Resistor |
Resistor used to set the R*C time Constant of a timiing circuit. |
| Transient Protection |
The prevention of malfunction or failure of a timer due to power line transients. Protection is usually provided by proper circuit design and/or suppression devices and is specified as a maximum voltage and time duration. |
| Transients |
Spurious voltage spikes on a power line that can produce false triggering impulses and/or cause insulation and component breakdowns and failures. Usually caused by load switching or inductive devices. |
| Triac |
A solid state switching device that controls an A.C. load. |
| Zero Voltage Switching |
Action that provides output switching only at the zero voltage crossing point of the ac sine wave. |
| Zero Voltage Turn Off |
Action that provides output switching to the OFF state only at the zero voltage crossing point of the ac sine wave. |
