Week 01 of 15 – Terms	Name: Answer Sheet

In your own words, write a definition for each of the following terms. Plagiarism will be checked and not tolerated.

Points: 5 pts/each = 18 * 5 = 90 pts

Process Variable (PV)

The dependent variable that is to be controlled in a control system.

Any variable property of a process. The term process variable is used in the relevant standard to apply to all variables other than instrument signals.

In the treatment of material, any characteristic or measurable attribute whose value changes with changes in prevailing conditions. Common variables are flow, level, pressure and temperature.

Process Instrument

A process instrument is a device used to directly or indirectly perform measurement within a process, the control of a process and/or the manipulation of a final control element. The instrument can perform any or all of these functions.

Measurement

The determination of the existence or of the magnitude of a variable.

Control

To control a process variable (PV) to be maintained at a specified value or within specified limits or to be altered in a specified manner.

Manipulation

To cause a final control element to directly change a process variable (PV) in order to achieve control of another process variable (PV).

Loop

A combination of one or more interconnected instruments that are arranged to measure and/or control a process variable (PV).

Primary Element

A sensing device that detects the condition of the process variable (PV).

Controlled Quantities

Controlled Quantities or Controlled Variables, are those streams or conditions that the practitioner wishes to control or to maintain at some desired level.

The variable that the control system attempts to keep at the set point

The part of a process to be controlled.

Manipulated Quantities

The independent variable in a process control system that is used to adjust the dependent variable, the process variable. Also known as the manipulated variable.

Disturbances

Any signal or event that enters the process and tends to drive the control variable (CV) away from the desired value or set point.

An undesired change in a variable being applied to a system that tends to affect adversely, the value of a controlled variable.

Direct Measurement

A direct measurement is any measurement that is in contact with the quantity being measured. As an example: a flow meter measuring the amount of material passing through a pipe.

Inferred Measurement

An inferred measurement is a method of measuring one variable to determine the value of another variable. As an example: measuring pressure to determine rate of flow.

Range

The region between the limits within which a quantity is measured, received, or transmitted. It is expressed by stating the lower and upper limits of variation.

Full Scale (FS)

The maximum absolute value for which a device is specified.

The largest value of a measured quantity that can be indicated on an instrument scale.

Span

The algebraic difference between the lower and upper limits of a range.

Instrument Symbol

A graphic representation of an instrument used on a Process & Instrumentation Diagram (P&ID).

Tag Number

The identification number for an instrument loop.

Set Point (SP)

An input variable that sets the desired value of the control variable (CV).