The minimum graduation of a pressure gauge can be simply understood as its resolution, but it is not necessarily the accuracy of the gauge.
Because a pressure gauge is a measuring instrument, it displays a measured value to us, and there is a certain error between the measured value and the true value. This error range is actually the accuracy, so the smaller the numerical value of the accuracy, the closer the displayed value of the measuring instrument is to the true value, and the higher the reliability.
I. Accuracy level verification of pressure gauges
The accuracy level of a pressure gauge refers to the percentage of the full-scale range allowed for the gauge's error.
Under reference working conditions, the accuracy level verification of a pressure gauge should include the following four items:
The indication error should not exceed the allowable error specified in Table 2 within the measuring range.
The hysteresis error should not exceed the absolute value of the allowable error specified in Table 2 within the measuring range.
After tapping the gauge casing lightly, the variation of the pointer indication should not exceed half of the absolute value of the allowable error specified in Table 2.
Pointer deflection stability
Within the measuring range, the pointer deflection should be stable without any jumping or sticking phenomena.
II. Meaning of accuracy level of pressure gauges
The accuracy level of a pressure gauge is expressed as the percentage of the full-scale range allowed for the gauge's error. Generally, there are seven levels of accuracy: 0.1, 0.16, 0.25, 0.4, 1.0, 1.6, 2.5, and 4.0. Among them, the accuracy levels of 0.1, 0.16, 0.25, and 0.4 belong to precision pressure gauges and are used in occasions with relatively high requirements for accuracy. The others belong to commonly used pressure gauge levels. For example, the accuracy of Y-60 is generally 2.5, and the accuracy of Y-100 and Y-150 is generally 1.6.
For example, for a pressure gauge with a dial range of 0-2.5MPa and an accuracy level of 2.5, the allowable error between the pressure value indicated by the pointer and the actual pressure value of the measured medium should not exceed ±0.0625MPa, which is 2.5% of the upper limit of 2.5MPa. When the pressure gauge indicates a pressure of 0.8MPa, the actual air pressure is between 0.7375 and 0.8625MPa.
Therefore, the actual error of a pressure gauge not only depends on the accuracy but also on the range of the pressure gauge. When the range is the same, the higher the accuracy (i.e., the smaller the number), the smaller the allowable error of the pressure gauge. When the accuracy is the same, the larger the range, the larger the error of the pressure gauge.