On the dial of a pressure gauge or a dial thermometer there is a lot of information. This is described in the EN 837 and EN 13190 standards and must be noted when reading. What is this information, what are the differences between pressure gauges and thermometers and what should be taken into account when reading them?
Basically, on mechanical measuring instruments such as pressure gauges or even bimetal and gas-actuated thermometers, the measured values are indicated by the pointer.
On the dial you will find the following elements and information:
The unit, such as bar, psi, kPa in pressure measurement, or degrees Celsius and degrees Fahrenheit in temperature measurement.
The accuracy class
On a pressure gauge, this indicates by what percentage the display may deviate from the scale value. Typical accuracy classes for pressure gauges are 0.6, 1.0, 1.6 and 2.5, for example. For dial thermometers, accuracy classes 1 and 2 are available. These classes indicate, depending on the scale range, how many degrees the maximum error limit is (in accordance with EN 13190).
The scale is very important for the correct reading of the measuring instruments. Pressure gauges have a scale of exactly 270 (angular) degrees. For dial thermometers, this scale may deviate up to 20 (angular) degrees.
A distinction between scale range and measuring range is only found in thermometers. The measuring range for which the accuracy class is specified is indicated by black triangular symbols. On pressure gauges you can also see a triangle, but this is the label for the maximum pressure with static loading, thus, how much of a permanent pressure load the pressure gauge may be exposed to without any damage.
On the dials, further important information is printed. For example:
– the standard in accordance with which the instrument was built,
– the material of the components which are in contact with the medium,
– the serial number of the measuring instrument.
Some pressure gauges also have an S within a circle, this symbol means that it is a safety pressure gauge “S3” in accordance with EN837-1 with a solid baffle wall, blow-out back and laminated safety glass.
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