H
Technical Terms
149
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 with
out 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 (X
L
), and capacitive reactance (X
C
).
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.
Technical Terms (cont.)
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