Monday, 22 August 2022

INSTRUMENT RANGE SELECTION

 Choice of instrument range

The range of the instrument is chosen based on the operating range of the process to be measured. In common practice, it is recommended to select a full-scale instrument that can provide an operating reading between 30% and 70%, especially for a pressure gauge. The following is an example of selecting a pressure gauge range


Given process data:

Minimum operating pressure: 5 kg

Maximum operating pressure: 9.5 kg

Maximum design pressure: 25 kg


Available standard pressure gauge range: 0-10 kg, 0-16 kg, 0-25 kg


[X] A selection of 0-10 barg will provide a 95% reading during maximum operating conditions. The device has only a small reserve above the maximum operating pressure.


[√] Selecting a range of 0-16 barg will provide the best reading during operating conditions. However, the maximum gauge pressure is normally 1.3x the maximum scale, which is only 16×1.3 = 20.8 barg. In such a case, the gauge must be equipped with over-range protection to withstand the design pressure.


[X] The 0-25 kg selection can withstand up to 32.5 kg (25 x 1.3) without using overrange protection, but under normal operating conditions this would give a poor reading indication.

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