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I am studying static and dynamic characteristics of instrument/ sensor these days since many term are used interchangeably so this create confusion. The best thing is to stick to definition given in ISA standards. Now I two terms for which ISA standard had given separate definition. May be due to my weak English I could not differentiate between them. Can you kindly help me?
The terms are Drift and Stability.
drift
1. An undesired change in output over a period of time, where the change is unrelated to the input, environment, or load. See ANSI/ISA-S51.1-1979 (R1993). [ISARP67.04.01-2000.ISA-RP67.04.02-2000]
2. An undesired change in the output/input relationship over time. [ANSI/ISA-75.05.01-2000] 3. An undesired change in output overtime that is not a function of the measurement.[ISA-37.1-1975 (1992)]
3. Drift is usually expressed as the change in output over a specified time with fixed input and operation conditions. It is usually used in the context of analog transducers, analyzers, and so on.
stability
1. The ability of a transducer to retain its performance characteristics for a relatively long period of time. Note: Unless otherwise stated, stability is the ability of a transducer to reproduce output readings obtained during its original calibration, at room conditions, for a specified period of time. It is then typically expressed as "within [number] percent of full scale output for a period of [number] months." [ISA-37.1-1975 (R1982)]
2. In data processing, a measure of the ability of a device to maintain constant volumes for one or more parameters that describe its operation. [ISA-RP55.1-1975(R1983)]
3. Freedom from undesirable deviation.
4. A measure of the controllability of a process.
Actually these two terms are used quite interchangeably. I have found that when we are calibrating an instrument and it has an offset we say it had drifted. Similarly most test equipment (Like Dry Bath Calibrators) has stability (both long term stability and short term stability) in their specification. As an aside stability is also used to define a process controller that returns the process to new set point after disturbance. But at that time we know that we are dealing with a process. But how do we differentiate between these two when looking only at sensor/instruments.
Can you please explain these two terms by giving examples and differentiating between them?
Are both of these term separate characteristics of an instrument?
Can you please provide me additional resources from where I can get explanation for these terms?
The terms are Drift and Stability.
drift
1. An undesired change in output over a period of time, where the change is unrelated to the input, environment, or load. See ANSI/ISA-S51.1-1979 (R1993). [ISARP67.04.01-2000.ISA-RP67.04.02-2000]
2. An undesired change in the output/input relationship over time. [ANSI/ISA-75.05.01-2000] 3. An undesired change in output overtime that is not a function of the measurement.[ISA-37.1-1975 (1992)]
3. Drift is usually expressed as the change in output over a specified time with fixed input and operation conditions. It is usually used in the context of analog transducers, analyzers, and so on.
stability
1. The ability of a transducer to retain its performance characteristics for a relatively long period of time. Note: Unless otherwise stated, stability is the ability of a transducer to reproduce output readings obtained during its original calibration, at room conditions, for a specified period of time. It is then typically expressed as "within [number] percent of full scale output for a period of [number] months." [ISA-37.1-1975 (R1982)]
2. In data processing, a measure of the ability of a device to maintain constant volumes for one or more parameters that describe its operation. [ISA-RP55.1-1975(R1983)]
3. Freedom from undesirable deviation.
4. A measure of the controllability of a process.
Actually these two terms are used quite interchangeably. I have found that when we are calibrating an instrument and it has an offset we say it had drifted. Similarly most test equipment (Like Dry Bath Calibrators) has stability (both long term stability and short term stability) in their specification. As an aside stability is also used to define a process controller that returns the process to new set point after disturbance. But at that time we know that we are dealing with a process. But how do we differentiate between these two when looking only at sensor/instruments.
Can you please explain these two terms by giving examples and differentiating between them?
Are both of these term separate characteristics of an instrument?
Can you please provide me additional resources from where I can get explanation for these terms?
