Note on Dynamic Performance Parameters

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Dynamic characteristics:

When an input is applied to the instrument,it can’t take up final steady state position immediately. The system goes through the transient state before it finally settles to its final steady-state position. Thus, The set of criteria defined for the instruments, which changes rapidly with time, is called ‘dynamic characteristics’. The term dynamic characteristics are used to study the behavior of the system between the time that the output value changes and time ,that value has settled to its final steady-state value.

Response curve to show static and dynamic characteristics of the instrument.
Response curve to show static and dynamic characteristics of the instrument.

The various Dynamic characteristics are:

i) Speed of response

ii) Measuring lag

iii) Fidelity

iv) Dynamic error

v)Frequency response

vi)Bandwidth

vii)Signal to noise ratio

viii)damping factor

ix)rise time

x)settling time

Some of them are explained below:

1.Speed of response:

It is defined as the rapidity with which a measurement system responds to changes in the measured quantity. It shows how active and fasts the system is.

2.Measuring lag:

It is the retardation or delay in the response of a measurement system to changes in the measured quantity. The measuring lags are 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 a dead time after the application of the input.

3.Fidelity:

It is defined as the degree to which a measurement system is capable of faithfully reproducing the changes in input, without any dynamic error.

4.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.

References-

1.S.morris.alan(2001). Measurement and Instrument principle(3 ed.).A division of Reed Educational and Professional Publishing Ltd

2.nderson, Norman A. (1998). Instrumentation for Process Measurement and Control (3 ed.). CRC Press.



  • The set of criteria defined for the instruments, which changes rapidly with time, is called ‘dynamic characteristics’.
  • The speed of response,Measuring lag,Fidelity,Dynamic error,Bandwidth etc are the Dynamic characteristics of the instrument.
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