Static Characteristics

 

1. Accuracy: This is a measure of the accuracy of the transducer output representing the true value being measured. It is defined as

 

Ea = (Ot - Om)/Ot x 100%

 

where Ea is the error, Ot is the true value being measured, Om is the transducer or system output.

 

Accuracy is often defined in terms of a full scale output and is defined as

 

Es = (Ot - Om)/Os x 100%

 

where Es is the full scale error, and Os is the full scale output.

  

2. Precision: This is a measure of the deviation from a mean value computed from a set of readings obtained for a single given input. In other words the repeatability of a transducer reading is defined by the precision specified for a specific transducer.

 

3. Resolution: This is a measure of smallest incremented unit of the input signal that can be measured by the transducer.

 

4. Sensitivity: The ratio of the output to the input gives a measure of a transducer systemÔs sensitivity to a given input.

 

5. Drift: The change in the transducer output for a zero input or its sensitivity over a period of time, change in temperature, humidity or some other factor.

 

6. Linearity: The degree to which a given calibration curve fits a straight line within a range of the full scale output of the transducer. Linearity is often a desirable trait in instrumentation design. A transducer output may be non-linear over its entire range, but a portion of its curve over a limited range may be fairly linear; this range may be used in instrumentation design.

 

7. Conformance: For a non-linear transducer, the tightness of fit to a specified curve is known as conformance of conformity.

 

8. Span: The operational full scale range of the transducer is known as the span. The span is therefore defined as the difference between the maximum and minimum outputs of the transducer.

 

9. Hysteresis: The difference in transducer output Y for the same input X dependent on the manner in which the input signal X is varied.

 

10. Distortion: The difference of the actual output from the expected result as defined by a known linear or non-linear relationship (curve) of input and output for the transducer.

 

11. Noise: A signal generated by internal circuitry or external interference that is superimposed or added to the output signal.

 

The above characteristics of a transducer are generally determined by examining the output response of a transducer to various input signals. Test conditions simulate actual operating conditions as closely as possible. Standard statistical and computational methods can be applied to the test data. For further information refer to standard texts on laboratory practice and measurements.

 

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Please send questions or comments to Professor Ron Adrezin.