A B C D E F G H I K L M N O P R S T U V W
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 moveable contact (wiper), and one terminal fixed at one end of the resistance. A potentiometer can be connected as rheostat by connecting the wiper to either one of its other terminals.
RMS (Root Mean Square) Effective DC value of 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.
SPDT (Single Pole Double Throw) A type of contact configuration which consists of a Common contact, Normally Open contact, and 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 temperatures 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 3 kA. Of the two, the one which simulates lightning transients is the combination 8/20 ?S current and 1.25/50 ?S voltage wave form. The simulation of transients generated by switching large capacitive or inductive loads is represented by a 0.5 ?S –100 kHz ring wave.
Underwriter’s Laboratories Inc. (UL) Testing agency for products sold in the United States.
Volt The basic unit 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 measure in volts.
Voltage Drop See On State Voltage.
Watt The basic unit of power.
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