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Thursday, September 17, 2015

Dynamic characteristics of measurement system

Dynamic characteristics

The set of criteria defined for the instruments, which are changes rapidly with time, is called
‘dynamic characteristics’.

The various static characteristics are:

i) Speed of response
ii) Measuring lag
iii) Fidelity
iv) Dynamic error


Speed of response:
·         It is defined as the rapidity with which a measurement system responds to changes in the
measured quantity.
·         It gives the information about how fast the system reacts to the changes in the input.

Measuring lag:
·         Every system takes some time , whatever small it may be, to respond to the changes in measured variable. This retardation or delay in the response of a system is called lag.
 The measuring lags are of two types:
a) Retardation type:
In this case the response of the measurement system begins immediately after the change in
measured quantity has occurred.

b) Time delay lag:
In this case the response of the measurement system begins after some time called dead time after the application of the input. Such a delay causes dynamic error.

Fidelity:
·         It is defined as the degree to which a measurement system indicates
changes in the measurand quantity without dynamic error.
·         It is the ability of an instrument to produce a wave shape identical to wave shape of input with respect to time.

Dynamic error:
It is the difference between the true value of the quantity changing with time & the value
indicated by the measurement system if no static error is assumed. It is also called measurement
error.

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