Glossary

Glossary

A

Absolute position measurement

Position measured from a fixed point.

Absolute pressure

Pressure measured with reference to a perfect vacuum.

Accelerometer

A sensor for measuring acceleration or the rate of change of velocity.

Accuracy

A measure of the difference between the indicated value and the true value.

Actuator

A device that performs an action on one of the input variables of a process according to a signal received from the controller.

Analog to digital converter

A device that converts an analog voltage or current into a digital signal.

Aneroid barometer

A barometer that uses an evacuated capsule as a sensing element.

Anticipatory action

See also Derivative action.

B

Bellows

A pressure sensor that converts pressure into linear displacement.

Bernoulli equation

A flow equation based on the conservation of energy, which includes velocity, pressure, and elevation terms.

Beta ratio

The ratio of the diameter of a restriction to the diameter of the pipe containing the restriction.

Bimetallic

A thermometer with a sensing element made of two dissimilar metals with different thermal coefficients of expansion.

Bode plot

A plot of a transfer function (gain in decibels and phase in degrees) versus frequency (log scale).

Bourdon tube

A pressure sensor that converts pressure to movement. The device is a coiled metallic tube that straightens when pressure is applied.

British Thermal Unit

A measure of heat energy, which is defined as the amount of heat required to raise 1 lb of water 1 F at 68 F and 1 atm.

Buffer amplifier

A circuit for...