ACCURACY
For a mechanical pressure gauge, accuracy is defined as a percentage of the full-scale range.
While requirements differ from one industry to another, the following are general guidelines:
Test Gauges and Standards: 0.25% through 0.10% full scale accuracies.
Critical Processes: 0.5% full scale accuracy.
General Industrial Processes: 1.0% accuracy. Less Critical Commercial Uses: 2.0% accuracy.
DIAL SIZE
Pressure gauge dial sizes range from less than 1? to 16? diameters. Generally, readability require-ments, space limitations and required gauge accuracy determine dial size. Accuracies of 0.25% or 0.5% generally have dial sizes of 41?2? or larger since more dial graduations are required.
CASE STYLE / MATERIAL
Environmental considerations include ambient temperature, air-borne particulate, condensation, humidity, water and chemicals, all of which can affect gauge performance.
Ambient temperature may affect the accuracy and integrity of the gauge. Gauges are available either temperature compensated or non-temperature compensated. Ambient conditions may require that the gauge be isolated from temperature extremes. When required, the gauge should be isolated from temperature extremes with a flexible line assembly.
When ambient conditions are corrosive, contain a large number of particulate or if the gauge will be exposed to a wet or humid environment like humidity, wash-downs or rain, specify a gauge that is weatherproof/hermetically sealed or liquid filled.
MEDIA / WETTED PARTS
The wetted parts of the pressure gauge, the Bourdon tube and socket must be compatible with the process media. If not compatible with the wetted parts of the gauge, corrosion will occur. Corrosion of gauge wetted parts will eventually cause gauge failure and possibly safety issues. When the gauge wetted parts are not compatible with the process media, a diaphragm should be considered.
Factors to consider when selecting a pressure gauge connection include process pressures, gauge size and weight, space limitations, leak integrity, and past experience.
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