Glossary

This glossary contains ANSI terms and definitions related to meters and instrumentation.

Accuracy: The quality of closeness to a specified value under stated reference conditions. Accuracy is quantitatively expresses by uncertainty.

Accuracy, intrinsic: The limit of the accuracy of an instrument when used under reference conditions. Accuracy is expressed in percentage of the fiducial value. This concept of accuracy is concerned with the intrinsic qualities of the instrument as opposed to the variation in indication that may arise when the instrument is used under conditions other than the reference conditions. Intrinsic accuracy is the uncertainty of the instrument in the “as received” condition, without the applications of corrections from a chart, curve or tabulation.Accuracy, rated (class): The assigned classification, which represents the value of uncertainty that the intrinsic accuracy of the instrument will not exceed.

Balance: The change in the position of the pointer from zero when the axis of the moving element moves from the vertical position to the horizontal position. The balance is expressed as percentage of the scale length.

Damping: The manner in which the pointer settles at its steady indication after a change in the value of the measured quantity. There are two general classes of damped motion, as follows:

  • Periodic – in which the pointer oscillates about the final position before coming to rest.
  • Aperiodic – in which the pointer comes to rest without overshooting the rest position.

The pointer of change between periodic and aperiodic damping is called “critical damping”. A critically damped instrument is when overshoot is present but does not exceed an amount equal to half the rated accuracy of the instrument.

Error, pivot friction: Error caused by friction between the pivots and the jewels.

Error, Zero shift (residual deflection): The part of the deflection of a mechanically controlled moving element that remains after the excitation producing the deflection has been removed and all the measuring circuits are de-energized.

Full-scale value: The arithmetic sum of the two end-scale values. When zero is not on the scale, the full — scale value is the higher end-scale value.

Instrument Full-scale Value
0-150 150*
50-0-150 200*
150-0-150 300*
90-140** 400*

*When zero is on the scale

**When zero is not on the scale

Note: Certain instruments such as power-factor meters, are necessarily exempted from this definition.

Instrument, analog indicating: An instrument that continuously measures an electrical quantity and displays the result by a relationship between a pointer and gradual scale.

Instrument, permanent-magnet moving-coil: An instrument designed that operationally depends on the reaction between the current in a movable coil(s) and the field of a fixed permanent magnet.

Instrument, self-contained: An instrument that has all necessary equipment and components built into the case or integrated within.

Instrument, suppressed-zero: An instrument in which the lower portion of a given scale does not appear and cannot be indicated and where the zero is displaced outside the scale by mechanical or electrical means.

Instrument, shunt: A resistor intended to be connected in parallel with an associated instrument in order to produce a higher current range that can be obtained by the instrument alone. The resistance of the shunt may be so chosen that the ratio of current measured by the combination to the current measured by the instrument alone is known.

Pointer shift due to tapping: The displacement in the position of a moving element that occurs when the instrument is tapped lightly. The displacement is observed by a change in the indication of the instrument.

Range: The region between the limits of display within which the input quantity is measured. Range is expressed by stating the lower and upper values of the display. (Examples: 0-100, 70-140, 50-0-50).

Repeatability (hystersis): The ability of an instrument of repeat its indications when the pointer is deflected upscale compared to the indications taken when the pointer is deflected downscale. Repeatability is expressed as a percentage of the fiducial value.

Response time: The time required after an abrupt change of the measured quantity to a new constant value until the pointer or indication means first comes to apparent rest in its new position.

Scale: The array of calibrated marks from which the input quantity may be read and interpreted.

Sticking: The condition caused by physical interference with the normal motion of the moving element.

Suspension, taut-band: A mechanical arrangement of two ribbons under tension, one at each end of the moving element. The ribbons support the moving element, allow it to rotate freely, provide the restoring torque, and conduct current to the moving element of moving coil instrument.

Tracking: The ability of an instrument to indicate at the scale mark being checked when energized by the proportional value of actual end-scale excitation.

Tracking error: The error indication at a scale mark, expressed in percentage of fiducial value, when the instrument is energized by the proportional value of the actuated end-scale excitation. On offset-zero indicators, the higher end-scale value should be used as the reference value.