Process Engineering Division – Instrumentation and Automation Section – Daily Topics – Topic No. 2020-12-01
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Process Engineering Division – Instrumentation and Automation Section – Daily Topics – Topic No. 2020-12-01: Discussion question: 313. What is instrument lag?
Time for process parameter changes to be received by the instruments/systems
Any talk of lag in the instruments is nonsense; it’s because the temperature, flow rate, and level of the process medium require time, need heat exchange, and must flow slowly, which is why this happens.
;P This guy is right – the instrument panel takes the blame! For normal instrument sensors, from the transmitter to the DCS, and for the DCS key scanning rate, all are within 200 MS; with configuration control added, the time up to display is generally within 500 MS. The delay in temperature is due to the time required for heat transfer through the medium, not a lag in the instrument. Chemical plants are more or less the same: their instruments are of poor quality and their systems are inadequate. The same products work well when used in other companies, while the control systems come from major manufacturers that are used all over the world. Matching is crucial; the suitability of the design and selection, as well as the appropriateness of the process parameters and control schemes, are all important factors.
Time for process parameter changes to be received by the instruments/systems
The lag of a controller refers to the phenomenon where the change in the controlled variable of the controlled object lags behind that of the disturbance.
Measurement lag leads to control lag, which is more noticeable in online analyzers; other instruments are less affected by this issue, so timely action is still necessary.
Time for process parameter changes to be received by the instruments/systems
The phenomenon in which the change in the controlled variable of a process control object (such as temperature/pressure/flow rate, etc.) lags behind that of the disturbance is called lag.
The time it takes for changes in process parameters to be detected by the instruments/systems. Under the same process conditions, it is necessary to determine whether the instrument that is used first has a method suitable to meet the required standards; if not, an instrument with a faster response time must be chosen in order to satisfy the process requirements. Instruments are used to meet the requirements of the process.