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Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Damping

The manner in which the pointer of an analog instrument settles at its steady indication after the applied electrical energy is changed. Usually expressed as percent over-shoot.

D'Arsonval Movement

A meter movement based upon the permanent-magnet DC motor principle: a small coil of wire supported on jewel bearings or taut band between the poles of a permanent magnet. The magnetic field of the DC current passing through the coil interacts with the magnet’s field, causing rotation of the coil and an attached pointer against the restoring force of coil springs.

dB (Decibel

20 times the log to the base 10 of the ratio of two voltages. Every 20dBs correspond to a voltage ratio of 10, every 10 dBs to voltage ratio of 3.162. For instance, a CMR of 120 dB provides voltage noise rejection of 1,000,000/1. An NMR of 70dB provides voltage noise rejection of 3,162/1.

Deadband (Hysteresis

In a digital controller, there may be one switching point at which the signal increases and another switching point at which the signal decreases. The difference between the two switching points is called hysteresis or deadband.

Delta Connection

A circuit formed by connecting three electrical devices in series to form a closed loop; most often used in three-phase connections.

Demand (active, real or true power

The power which is actually consumed by the load. This measurement takes the power factor into account.

Dielectric Strength

An instrument, which depends upon the magnetic reaction between a fixed, and a moving coil producing deflection of a pointer over a graduated scale. This type of movement responds to root-mean-square (RMS) or affective current. The ability to truly measure distorted waves having high peaks is far superior to other devices. Since by convention, scales are calibrated in RMS quantities, the electrodynamometer instrument can be used with equal accuracy on DC or AC. Watt, volt, amp, VAR and power factor meters use this construction. Frequency coverage can extend from DC to 2500 Hz with a cap from DC to 15Hz due to excessive pointer vibration.

Differential Input

A signal-input circuit where SIG LO and SIG HI are electrically floating with respect to ANALOG GND (METERGND, which is normally tied to DIGGND). This allows the measurement of the voltage difference between two signals tied to the same ground and provides superior common-mode noise rejection.

Differential Pressure

This is the difference of two pressures into a single gauge. It can be read in either a duplex version that shows the individual pressures or by a single readout that shows the actual difference between the two sources.

Digit

A measure of the display span of a panel meter. By convention, a full digit can assume any value from 0 through 9, a 1/2 digit will display a 1 and overload at 2, a 3/4 digit will display digits up to 3 and overload at 4, etc. For example, a meter with a display span of ±3999 counts is said to be 3-3/4 digit meter.

DIN (Deutche Industrie Norm)

A set of German standards recognized throughout the world. The 1/8 DIN standard for panel meters specifies an outer bezel dimension of 96 x 48 mm and a panel cutout of 92 x 45 mm.

Diode

Device that allows current to flow in only one direction.

Distortion Factor (%DF)

Total difference between apparent power and true power at all harmonic frequencies.

Divider

A resistance for connection across a voltage, tapped at one or more points to provide discrete fractions of the voltage.

Drift

A variation in a reading or set point value resulting from changes in component value, ambient temperature and line voltage.

Dual-Slope Conversion

A digital technique for converting a measured analog quantity to a precise digital equivalent, for display as a numerical value. During a fixed interval of time, the output of an integrating circuit rises linearly at a rate proportional to the measured analog input quantity. The circuit input is then switched to a precise reference-voltage source of opposite polarity, causing the output to descend at a fixed rate, while a counting circuit counts clock pulses delivered by an internal pulse generator. As the integrator output reaches its base level, the count is terminated; the total count (numerically equivalent to the analog input quantity) is then displayed in a digital readout as a voltage, current, resistance, or other parametric quantity.

Duplex Sensor

A dual element RTD or thermocouple usually isolated from each other and in the same housing or sheath.