## Tuesday, April 15, 2014

### Understanding Pressure Gauge Specifications.

Pressure gauges have many specifications which technicians should understand when selecting a gauge, including range, resolution, accuracy, proof pressure, and burst pressure.

The range is the lowest to highest reading on the gauge. It is important that the range of a gauge fit the pressures for which it will be used. You want a gauge able to read the highest pressure you might encounter, but you don’t want the top reading much higher than that. This is because accuracy is stated as a percentage of full scale. A gauge with an accuracy of 1% and a top reading of 300 psig has a possible error of 3 psi. If you make the top reading 600 psig, now the possible error becomes 6 psi. If the pressures you will be reading only go up to 250 psig, expanding the top pressure reading just makes the error larger.

Resolution is the smallest indication the gauge can display. A gauge that can display in tenths of a pound has a resolution of 0.1 psi. This is not the same as the accuracy. Just because a gauge CAN display in tenths of a pound does not mean the reading is accurate to tenths of a pound. However, having a small resolution does make the gauge more useful for precise readings than another gauge with the same accuracy and top scale. For example, there are both analog and digital gauges with the same accuracy, but an analog gauge with a scale of 0 – 500 psig cannot have a resolution in tenths of a pound – there is just not enough space. A digital gauge with the same accuracy and top reading has no problem displaying in tenths of a pound.