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AC (Alternating current) An electric current that reverses direction in a circuit at regular intervals.
Accuracy The variation between the specified delay time and the Actual Time value, given in percent of specified delay. Actual Time - Specified Delay Time) / Specified Delay Time)) x100.
Actual Time The actual delay of a given device with sufficient "off" time of input voltage to permit full recovery of the timing interval. The resulting average of a group of consecutive time delay readings (excluding the first) may be used to determine the Actual Time. Five cycles should be considered adequate for this determination.
Ambient Temperature Temperature of the air which encircles an object.
Ampere (AMP) The basic unit of electric current.
Arc A luminous discharge of electric current crossing a gap between two electrodes either through the air or over an insulated surface. An effect which proves deleterious to electromechanical switches which consequently limits contact life.
Break The moment and/or location at which a series circuit is opened and made discontinuous.
Brownout A condition in which the supply voltage is insufficient to power the load.
Circuit A closed path followed or capable of being followed by an electric current.
Closure The moment and/or location at which two contacts meet to complete a circuit.
Conductor A substance or medium that conducts heat, light, sound, or especially an electric current.
Contact Chatter (Contact Bounce) Occurs when an electromechanical switch is in the process of making connection in a circuit; for a brief time period, the contacts will bounce together until they are fully seated.
Contacts Electromechanical components that make or break a connection between two conductors that permit a flow of current.
Controller A regulating mechanism, as in an electric device used to control a particular process based on input parameters.
CSA Canadian Standards Association. (Testing Laboratory for products sold in Canada.)
Current The amount of electric charge moving in a conductor past a specified circuit point within a given time. The basic unit is the Ampere.
Cycle A single complete execution of a periodically repeated event or a periodically repeated sequence of events.
De-energize To remove power from a device.
Delay To postpone an event until a later time.
Delay On Break (Off Delay) A particular type of timing function whereby the OFF event is delayed after a start circuit is opened.
Delay on Make (Delay on Energize, On Delay) A particular type of timing function which delays the ON event upon initial application of power to the timing device.
Dielectric Breakdown The voltage potential at which the insulating properties of a non-conductor will break down and conduct current. Measured in kilo-volts.
Direct Current (DC) An electric current flowing in one direction (constant polarity) as opposed to Alternating Current which periodically changes polarity.
Double Pole Double Throw (DPDT, 2 form C contacts) A type of contact configuration which consists of two isolated sets of contacts operating simultaneously. Each contact set consists of a: Common contact, Normally Open contact and a Normally Closed contact. In relay nomenclature, the states of the contacts are given with the relay coil unenergized.
Electricity A basic phenomenon in nature which involves the movement of electrons in a medium. This movement of electrons or electric current is considered a source of power.
Electromotive Force (EMF) Difference in electrical potential measured in volts.
Encapsulant A compound, typically epoxy or silicone elastomer used to envelop and seal components in an electronic circuit.
Energize To apply power to a device.
External Adjustment A remotely located component or device which is used to alter an input or output parameter on a controller.
Factory Calibration To adjust a controller during the manufacturing process to specific points in order to meet the operational specifications.
Factory Fixed Fixing a particular control parameter during the manufacturing process to make it non-adjustable in the field.
Frequency The number of repetitions within a given time of a complete wave form, as of common Line Voltage with typical frequencies of 50 or 60 cycles per second. See Hertz
Full-wave Rectified AC Alternating Current changed to Direct Current utilizing both the positive and negative portions of the AC sine wave.
Ground The point of an electric circuit that is at a zero volt potential with respect to the earth.
Guaranteed Range The range of operation of a controller or controlled parameter which the manufacturer specifies reliable consistent operation.
Heat Dissipation Because all electrical devices offer resistance to the flow of current, heat will be generated (dissipated) when current is flowing through this resistance. This undesired heating effect is a function of the device resistance and the amount of current that is flowing through it. Heat Sinks are used to cool high current devices.
Heat Sink A device which possesses low thermal resistance in order to effectively transfer dissipated heat to the ambient temperature.
Heat Sink Compound A compound which is used to assure a good thermal connection between a heat dissipating device and a heat sink.
Hertz A unit of frequency named after Heinrich R. Hertz (1857-1894) which is equal to one cycle per second.
Holding Current In solid state switching devices there is a point at which the current flow is insufficient to maintain conduction. Holding current is specified as the minimum current through the device across the operating temperature range that will maintain conduction.
Horsepower A unit of power in the U.S. Customary System, equal to 745.7 watts or 33,000 foot-pounds per minute. Electrical motors are rated in horsepower, so accordingly, devices designed to control motors are also rated in horsepower.
Humidity Water vapor content in the air. In percent Relative Humidity, it is a measurement of the actual water vapor content of a unit volume relative to what the maximum amount of water vapor the same volume can contain at a given temperature.
Hysteresis The failure of a property that has been changed by an outside force to return to its original value when the cause of the change is removed. Some hysteresis is designed into controller circuits because it prevents noise from causing false triggering.
Incandescent Lamp From a switching perspective, the incandescent load represents an initial inrush current of up to 10 times the steady state rating.
Inductive Load An inductive load opposes any change to circuit current. Devices such as motors, solenoids, relay coils, valves, and contactor coils are all inherently inductive loads. The current waveform is always lagging the voltage waveform in an inductive load; because of this phenomena, certain factors must be taken into account when working with this type of load. An inductive load can exhibit an inrush current of up to 5 times its normal running or steady state current when energized. When power is removed from the inductive load, high voltage transients are generated due to the collapsing magnetic field and this can cause arcing across contacts or a malfunction, and/or damage to electronic circuits.
Initiate Time (Start time) The minimum time of a switch closure or voltage pulse applied to a start switch input of a controller which will activate the control function.
Input Voltage The voltage source applied to the controller input terminals which is used to power the controller while it is performing its function.
Inrush Current The peak value of current which a load requires when first being energized. Certain types of loads (i.e. lamps, motors) will draw a larger initial current because their impedance is lower at startup than during steady state operation.
Isolation No electrical connection between two or more circuits.
Insulation Resistance The degree of non-conductance of an insulator measured in Megohms.
Insulator A material that insulates, particularly a nonconductor of electricity, heat, or sound.
Interval A period of time which occurs between events.
Kilohm One thousand ohms (1,000 or 1 K ohms).
Leakage Current The maximum current which a solid state device still conducts when in the OFF state. Leakage current is usually measured in milliamperes (mA).
LED Light emitting diode used in information displays and as status indicators.
Life A specific number of operations or amount of time during which a particular device is expected to operated reliably.
Line Frequency Frequency of electrical service provided by local utility, typically 50 or 60 Hertz.
Line Voltage Initiation The initiation of a control function by application of line voltage to either the controller's input terminals or start switch terminals.
Line Voltage Nominal voltage of electrical service provided by local utility, typically 120 or 240 volts AC.
Load Any device which consumes power to do work.
Load Rating A specification of the output capability of a particular controller. Typical parameters for load rating are: controllable current range, maximum AC and/or DC voltage, Horsepower or Power Factor and maximum inrush current.
Lock Shaft (Locking Bushing) A mechanical means to inhibit further adjustment of a rotary type device such as a potentiometer.
Low Voltage Voltage which is typically less than 30 Vrms.
Magnal Plug A circular eleven pin male connector with an indexing key for proper orientation in the mating socket.
Make A term used to denote the action of completing an electrical circuit.
Metal Oxide Varistor (MOV) A device whose impedance decreases dramatically when subjected to voltages greater than the rated clamping voltage. It is typically placed in parallel with the input and/or output of a switching device to effectively clamp transient voltage spikes to a certain level.
Megohm One million ohms (1,000,000 or 1Meg ohms).
Micro - A Metric prefix which is used to multiply a standard unit by 10-6.
Milli- A Metric prefix which is used to multiply a standard unit by 10-3.
Milliamperes One-one thousandth of an ampere (.001 or 10-3 ampere).
Milliseconds One-one thousandth of a second (.001 or 10-3 second).
Minimum Load Current For electromechanical contacts, it is the minimum current the contacts will reliably switch without the contact resistance contributing a substantial error in the circuit. See Holding current.
Mode of Operation Logical function of a controller based on input parameters.
Momentary Initiation The initiation of a controller cycle by a start pulse of shorter duration than the complete cycle. The initiation could be with a momentary contact closure or voltage pulse.
Momentary Loss of Power (see Brownout) A short removal of input power to the controller or controlled circuit.
Momentary Switch A spring loaded set of contacts, when the actuator is pressed, the contacts either close or open depending on contact configuration. When the actuator is released the contacts will resume their normal state.
MOV Metal oxide varistor.
Noise An undesirable electrical phenomenon which is generated by various means (i.e. switching large loads , light dimmers, electrical storms). This phenomenon consists of random voltages and currents induced into electrical circuits, if severe enough, erratic operation of these circuits can result.
Nominal Voltage The middle point of two extremes of voltage as defined by the tolerance.
Normally Closed Contact (N.C.) The condition or position of a particular contact with respect to a common contact in its normal or quiescent (unenergized) state. A normally closed contact represents a closed circuit.
Normally Open Contact (N.O.) The condition or position of a particular contact with respect to a common contact in its normal or quiescent (unenergized) state. A normally open contact represents an open circuit.
Octal Plug A circular eight pin male connector with an indexing key for proper orientation in the mating socket.
Offset A fixed difference between the controller setpoint and the actual control point of a system under stable operating conditions.
Ohm A unit of electrical resistance and impedance named after Georg S. Ohm. A conductor has a resistance of one ohm when a current of one ampere flows through it with a potential of one volt across its terminals.
ON/OFF Time Ratio The ratio of ON time to OFF time specified as a fraction or percentage of the total period.
On State Voltage The voltage measured across a solid state output device when it is in the ON state. For all practical considerations the value is the same for Peak or RMS measurements. NOTE: The portion of the sinewave before the solid stste device turns ON is not to be included in this measurement.
Operating Temperature The range of ambient temperature in which a controller is designed to operate within its specifications. May be stated in Fahrenheit of Celsius.
Operating Voltage The range of input voltage in which a controller is designed to operate within its specifications. Usually, it is stated as a nominal value with a maximum and minimum tolerance (i.e. 120 VAC ± 10%).
Optical Isolation Utilizing light to isolate one control circuit from another; mainly used to safely interface a low level control signal to a high power output as in a solid state relay.
Output That section of the control which produces the desired result of the controller based on its inputs.
Parallel A type of circuit connection in which loads are connected side by side across a common voltage source.
Phase The instantaneous angular position which a sine wave occupies in its cycle. The position is usually measured in degrees as referenced to zero and referred to as phase angle.
Polarity The positive and negative orientation of a source of power or signal.
Potential Difference The voltage differential between two points.
Potentiometer (POT) A three terminal device which consists of a fixed resistor with terminations on each end and a moveable contact (wiper) that can travel between the two terminations. Also called a variable resistor.
Power In a Direct Current circuit it is the product of applied potential difference and current. In an Alternating Current circuit it is the product of the effective values of the voltage and current with the cosine of the phase angle between current and voltage. The units of measurement are VA or the Watt.
Power Factor The ratio of true power to apparent power in an alternating current or a ratio of resistance to impedance.
Quick Connect Terminals (Faston) A solderless friction type termination used in industrial controls to facilitate easy field wiring of electrical control systems.
RC Resistor/capacitor network. (See also Snubber Network).
Rectifier (Diode) An electronic device which allows current to flow in only one direction. It is used to convert AC to DC.
Repeatability (Repeat accuracy) The percent variation of time within a group of consecutive timing cycles, starting with the second operation, when the timing device is operated under constant conditions of operating voltage, ambient temperature, and on/off times.
Reset Time The time a controller takes to return to its initial parameters when input power is removed.
Resistance The opposition to electric current flow. All conductors offer some resistance and the basic unit of resistance is the ohm.
Resolution The degree of accuracy to which a controller can be set to or the degree of accuracy of an output function as in a digital readout of a specific output.
Rheostat A variable resistor having one movable contact (wiper), and one terminal fixed at one end of the resistance. A potentiometer can be connected as a rheostat by connecting the wiper to either one of its other terminals.
RMS Root Mean Square, Effective DC valueof sinewave voltage or current. The effective value is ,707 times the peak voltage or peak current measured.
Series Circuit Loads connected end to end across a voltage source.
Set point The point at which a controller will perform a function. The setpoint can be either factory fixed or user adjustable as in a temperature controller or a timer.
Setting Accuracy The degree of accuracy (resolution) to which a controller setpoint can be adjusted.
Shunt A low-resistance connection between two points in an electric circuit that forms another path for a large portion of the current.
Single Pole Double Throw (SPDT) A type of contact configuration which consists of a Common contact, Normally Open contact, and a Normally Closed contact. In relay nomenclature, the states of the contacts are given with the relay coil unenergized.
Snubber Network Typically a series connection of a resistor and capacitor applied across an output device (especially solid state) to minimize voltage spikes due to line transients or load switching. It is used to help prevent unwanted switching of solid state devices and arcing of mechanical contacts.
Specified Delay Time The advertised time, design print specified time, or set time of the delay function.
Steady State The condition of a device after power has been initially applied for a certain period or when its electrical parameters are allowed to stabilize. This condition is reflected in parameters such as current flow, output voltage, and/or temperature.
Storage Temperature The range of ambient temperature in which a controller is designed to be stored in order to assure operation within its specifications. May be stated in Fahrenheit or Celsius.
Termination The point at which electrical devices are connected to field wiring of either inputs or outputs. Typical types of termination are: Quick connect terminals, screw terminals, flying leads etc.
Time Diagram A logic function drawing used to relate the output operation of a particular controller with regard to its input parameters over a given period of time.
Tolerance The permissible deviation from a specified value of an electrical parameter. Normally stated as a percentage of a nominal value.
Transient A momentary occurrence of a particular phenomenon.
Transient Voltage Voltage spikes of short duration which occur in electrical circuits that exceed the normal designed operating levels. Two main types of voltage transient wave forms are generally used by the industry to define the typical transients found in the field, they are defined in the IEEE C62.41 standard (IEEE Recommended Practice on Surge Voltages in Low Voltage AC Power Circuits). Transient surges considered in this section do not exceed one-half period of the applied AC line frequency. Also, the magnitude of the crest voltage and current are designated as a peak open circuit voltage of 6 KV and a peak short circuit current of 3KA. Of the aforementioned two, the one which simulates lightning transients is the combination 8/20 uS current and 1.25/50 uS voltage wave form. The simulation of transients generated by switching large capacitive or inductive loads is represented by a 0.5uS - 100kHz Ring Wave.
Underwriter's Laboratories Inc. (UL) Testing agency for products sold in the United States.
Volt The basic unit of electromotive force or potential difference.
Voltage The difference in electrical potential, or electromotive force between the terminals of a source of electricity. It is usually measured in volts.
Voltage Drop See On State Voltage.
Watt The basic unit of power.
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