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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