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Individual Instrument calibration Vs. Loop calibration
29 July 2019 - 18:12, by , in Calibration, No comments

When calibration gets performed by disconnecting the Input and Output, it comes under the banner of Individual Instrument calibration.

  • Throughout the instrument’s calibration range, output can be measured on various data points by applying a known value of input.
  • By doing so, correct instrument can be adjusted.
  • Since calibration is getting performed on individual instrument so compatibility with multifunction calibrators can be achieved. 
  • It takes way too much time to check each instrument independently in comparison to Loop testing in which all loop instruments can be checked altogether.

When calibration of set of instruments gets performed together within a single loop, it comes under the banner of Loop Calibration.

  • Pass / Fail Calibration status can be determined by observing the relationship between Input and Output values of a complete loop and not individual instruments within it.
  • Entire loop (Sensor and Loop components) can be verified against tolerance.
  • Since calibration is getting performed in a loop so compatibility with multifunction calibrators can be compromised.
  • It doesn’t take too much time as we don’t need to check each instrument separately.


Figure: 1 Source Maximo Calibration.

Note: RTD or Thermocouple as temperature sensing element senses the temperature and sends signal in Ohms and Millivolts respectively to temperature transmitter which in turn transmits milliamperes signals to local display with which it is connected and finally to DCS. The signal is displayed on display units which is used to control the process.

End to End Loop Testing Vs. Portion of Loop

End to End Loop Testing

Partial Loop Testing

Temperature element (RTD / Thermocouple) need to be removed from the process and inserted in temperature bath so that process temperature can be simulated as per Technician’s choice.

When Temperature sensing probe cannot be inserted in temperature bath or it becomes difficult or costly to disconnect the probe from the process, partial loop testing can be performed.

Displayed final measurement (showing Transmitter XMTR readings) will be compared to simulated process readings (Sourced from temperature bath) and the difference in values can be observed.

Temperature sensing element will be disconnected from the transmitter’s end and temperature calibrator will be used to simulate a signal to the temperature transmitter



About author:
Fahid completed his Electrical Engineering from Pakistan in 2011 and Msc Quality Management with Distinction from United Kingdom in 2018. Along with the couple of Certifications and Training, he holds Technical and Managerial expertise within the field of Automation, Instrument Calibration, Testing, Quality and Operations Management. He is enthusiast about content writing specifically related to Inspection and Testing Business.

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