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Technical References
Glossary of Technical Terms
Accuracy
The degree of uncertainty with which a measured value agrees with the ideal values. Accuracy class of instrument transformers are defined by the requirements of ANSI standard number C57.13. Standard metering accuracy classes are 0.3, 0.6 and 1.2
Ambient Temp
Temperature of the surrounding air.
Apparent Power
The product of the applied voltage and current in ac circuit. Apparent power, or volt-amps, is not the true power of the circuit since power factor is not considered in the calculation.
Auxiliary Power
A power source, other than that producing the measured input quantity, which supplies the power necessary for the correct operation of the transducer.
Average Responding
The measurement of an AC voltage or current obtained using a DC instrument with a rectifying input circuit that converts AC energy to DC. The meter scale or readout is usually calibrated in terms of the corresponding RMS values, but is accurate only for pure sinewave inputs.
Burden
In current or potential transformers burden in VA is the maximum load the transformer can support while operating within its accuracy rating.
Calibration
Adjustment of a transducer so the output is within a specified range for particular values of the input.
Current Transformer
An instrument transformer used to accurately scale ac currents up or down, or to provide isolation. Generally used to scalelarge primary or bus currents to usable values for measuring (or control) purposes. The current measurement range is expressed as the ratio of full scale primary current to full scale secondary current. The primary winding is connected in series with the conductor carrying the current to be measured or controlled. There are two classification of current transformers. Window type and Wound Primary type. In Window type current transformers the primary winding is provided by the line conductor and is not an integral part of the transformer. In Wound Primary type the primary winding is an integral part of the transformers and usually consist of more that one turn. Wound Primary transformers are used in applications that require very high accuracies or where high voltage isolation is required.
Delay on Energization
A term describing a mode of operation relative to timing devices. Delay begins when the initiate switch is closed, or on application of power to the input. Same as Delay on Make.
Delay on Make
Same as delay on energization.
Dielectric Strength
The continuous voltage a dielectric can withstand without deteriorating.
Effective Power
In ac measurements, effective power (measured in watts) equals the product of voltage, current and power factor (the cosine of the phase angle between the current and the voltage).
Full Scale (F.S.)
The specified maximum value of the input quantity being measured that can be applied to a transducer without causing a change in performance beyond specified tolerance.
Full Scale Output
The specified maximum output value for which the stated accuracy condition applies.
Guaranteed Range
Refers to a range of adjustment or operating range whereby the control device must at least operate or cover the "guaranteed" range.
Hysterisis
An error resulting from the inability of an electrical signal or mechanical system to produce identical readings or position when approached slowly from either direction. Also referred to as deadband.
Impedance
The opposition in an electrical circuit to the flow of alternating (AC) current. Impedance consists of ohmic resistance (R), inductive reactance (XL), and capacitive reactance (XC).
Inrush
The initial surge of current through a load when power is first applied. Lamp loads, induction motors, solenoids, contactors, valves, and capacitive loads all have inrush currents higher than the normal running or steady state currents. Resistive loads, such as heater elements, have no inrush.
Instrument Transformer
A transformer which is intended to reproduce in its secondary circuit, in a definite and known proportion, the current or voltage of its primary circuit with the phase relations substantially preserved.
Isolation
To be electrically separate. A measure of the strength of the dielectric providing the electrical division or separation.
Linearity
A measure of departure from straight-line response in the relationship of two quantities, where the change in one is directly proportional to a change in the other. Normally expressed as a maximum percentage.
Loop Powered
The transducer uses the power supplied to the output current measuring loop. No auxiliary power supply is required.
Loop Resistance
The electrical resistance, in ohms, of a complete transducer circuit exclusive of an instrument's internal resistance.
Non-Linearity
In an ideal system, the input-output relationship between variables is linear(i.e. straight line) Any departure from straight line is expressed as non-linearity.
Operating Voltage
A nominal voltage with a specified tolerance applied. The design voltage range to remain within the unit's operating tolerances.
Phase Angle
The difference in time by which an alternating signal lags or leads another signal. Phase angle may be a measure of power factor when used to indicate the relationship of a voltage to current signal for a non-resistive load. Phase angle may also be used to measure the different in phase between the primary and secondary of an current or voltage transformer.
Polyphase Wattmeter
A wattmeter consisting of 2 or 3 single phase wattmeters mounted in the same package. The watt sensing elements can be electronic transducers. A dual element wattmeter will measure power in a 3 phase system regardless of power factor, voltage or current variations between phases. Most common types are 2,2« or 3 element forms. In 4 wire circuits, with the 4th wire carrying current, the 2« or 3 element type is used. If there is voltage imbalance, only the 3 element units can be employed.
Power
A source or means of supplying energy. The unit of measurement is the watt. 1 Horsepower is equal to 745.7 Watts.
Range
Nominal operating limits, specified by the lowest calibration point to the highest calibration point.
Rated Output
The output at standard calibration
Ratios
The relationship between the primary input value divided by the secondary output value. For example: a current transformer that has a primary input value of 100 Amps and a secondary value of 5 Amps will have a Current Ratio of 100:5 and a Turns Ratio of 20:1. It is important to use the term Current Ratio for most applications because it defines the current handling capacity of wire used in the secondary winding. The Turns Ratio only refers to the winding ratio and does not define the current handling capacity of the either primary or secondary windings.
Real Power
Same as Effective Power.
Reactive Power
A component of apparent power (volt-amps) which does not produce any real power (watt) transfer.
Repeat Accuracy
The maximum deviation from one timing operation to the next.
Self Powered
The power required for correct operation of a transducer is supplied via the line being measured.
Separately Powered
The power required for correct operation of a transducer is supplied via an external or auxiliary power source, rather than via the line being measured.
Setting Accuracy
The ability to accurately set a knob, switch, or other adjustment to the time delay, or other monitored parameter.
Snubber Network
A form of suppression network which consists of a series connected resistor and capacitor connected in parallel with the output device. Helps to limit the maximum rate of rise of a voltage. Used to prevent false turn-on of solid state outputs.
Snubber
A resistance/capacitor or diode/resistor circuit used to dissipate transient energy peaks.
Transducer
A device for converting an electrical signal into a useable direct current or voltage for measurement purposes.
RMS
The effective value of alternating current or voltage. The RMS value equates an ac signal to a dc signal which provides the same power transfer.
True RMS Amps
The effective value of an ac signal. For an amp signal, true RMS is a precise method of stating the amp value regardless of waveform distortion. An ac measurement which is equal in power transfer to a corresponding dc current.
True RMS Volts
The effective value of an ac signal. For a voltage signal, true RMS is a precise method of stating the voltage value regardless of waveform distortion. An ac measurement which is equal in power transfer to a corresponding dc voltage.
Unbalanced Loads
Refers to an unequal loading of the phases in a paleface system (current and/or phase angle)
Watt
Unit of electrical power. WATTS=E*I*PF
VA
The product of the RMS voltage applied to a circuit and the RMS current, in amperes, flowing through it.
VAR(Volt-Amperes Reactive)
The unit of reactive power as opposed to real power (watts)
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