IMPORTANT TERMINOLOGY USED IN INSTRUMENTATION


Range

The range of an instrument means the value of minimum measurable value to maximum measurable value.


Lower Range Value(LRV)

The lowest value of the measured variable, that a device is adjusted to measure. For a calibrated instrument, the lowest measurable value or the input value for a zero percent output of the value of instrument is termed as LRV.


Upper Range Value(URV)

The highest value of the measured value, that a device is adjusted to measure. For a calibrated instrument, the highest measurable value or the hundred percent output of the value of instrument is termed as URV.


Span

It is the difference between URV and LRV is known as span or sometimes range of the instrument.


Span = URV - LRV.


Sensitivity

Sensitivity of a sensor is defined as the change in output of the sensor per unit change in parameter being measured. Sensor may have constant or variable sensitivities, in which cases they have a linear or nonlinear output.


Resolution

Resolution is defined as the smallest change that can be detected by a sensor. Resolution is the fineness to which an instrument can be read.


Response

The time taken by a sensor to approach its true output when subjected to a step input is referred to as its response.


Linearity

The ability of a measuring instrument to provides an indication having a linear relationship with a defined quantity. The instrument response graph will be straight line for a linear instrument.


Hysteresis

While checking the response of an instrument, the inputs are given in the ascending and ascending orders. Taking the response of the instrument there will be two different curves starting and ending at same points. This difference in response of an instrument is called hysteresis.


Accuracy

Accuracy is the degree of closeness of the measured value to the true value of variable being measured.


Precision

Precision is the reproducibility or repeatability with which repeated measurements of the same variable can be made under identical conditions.

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CALIBRATION

CONTROL VALVE

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