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.