Chapter_9_Control Loops

Discrete sensing element

A sensing element that stands alone or is individually distinct, connected to the transmitter by sensor wires.

Impulse tubing

A tube usually made of stainless steel that allows the process variable to be sensed by the sensor located in the transmitter.

Instrument scale

A range of ordered marks indicating the numerical values of the process variable.

Integrally mounted sensing element

A sensing element that is a physical part of the transmitter.

Linear scaling

A linear relationship between two scales (input versus output).

Lower range value (LRV)

The number at the bottom of the scale.

Operating range

The difference between the upper range value (URV) and lower range value (LRV) on a scale.

Scaling

The act of equating the numerical value of one scale to its mathematically proportional value on another scale.

Sensor

A device that detects the process variable; can be an integral part of a transmitter.

Signal converter transducer

Part of a transmitter that converts the process variable into a standard instrument signal.

Span

The algebraic difference between the URV minus the LRV of a scale, expressed as one number.

Standard signal

The language that instruments use to communicate with one another (e.g., 4-20 mA, 3-15 psig, or digital).

Upper range value (URV)

The number at the top of the scale.

Transmitter

An instrument that produces an output signal carrying measurement information to the next instrument in the loop.

Differential pressure transmitter

A type of transmitter that measures the difference between two pressures.

Calibration range

The set of values existing between the LRV and URV of a scale, expressed as two numbers.

Transducer

A device that converts one energy form into another.

Live zero

A feature of signals where the zero value is greater than true zero, aiding in easier error correction.

I/P (current-to-pneumatic) transducer

A device that converts an analog electronic signal (4-20 mA) into a pneumatic signal (3-15 psig).