Meaning of symbols on the dial of a pressure gauge

Some contain important information about the gauge

 15 November 2016

What can you learn about a pressure gauge by just looking at the dial? In addition to the measured pressure, there is still a lot of information you can read that is necessary for the use of the pressure gauge. This article covers all information and symbols which should be, mandatory or not, marked on the dial according to EN 837.

The unit of pressure

Bourdon tube

The bar is the preferred unit of pressure. If SI units are used, the indication will be displayed in kPa or MPa.
The marking is mandatory.

Diaphragm / Capsule

The bar is the preferred unit of pressure. The mbar is used for measuring ranges of 600 mbar or less. If SI-units are used, the indication will be in Pa, kPa or MPa.
The marking is mandatory.

The accuracy class

The accuracy class is always expressed as a percentage of the span and is associated with the nominal size of the manometer.

Bourdon tube

Defined classes: [0,1] – [0,25] – [0,6] – [1] – [1,6] – [2,5] – [4]
The marking is mandatory.

Relation: Nominal size – Accuracy class
Nominal size Accuracy class
0,1 0,25 0,6 1 1,6 2,5 4
40 and 50 X X X
63 X X X X
80 X X X X
100 X X X X
150 and 160 X X X X
250 X X X X X

Diaphragm / Capsule

Defined classes: [0,6] – [1] – [1,6] – [2,5] – [4]
The marking is mandatory.

Relation: Nominal size – Accuracy class
Nominal size Accuracy class
0,6 1 1,6 2,5 4
50 X X X
63 X X X X
80 X X X X
100 X X X X X
150 and 160 X X X X X
250 X X X

The type of pressure element

The kind of measuring element which is located inside the pressure gauge may be represented by a symbol on the dial.

Bourdon tube

The marking is not mandatory.
Type of Bourdon tube Symbol
C-type Symbol for a C-type Bourdon tube
Spiral Symbol for a spiral Bourdon tube
Coiled Symbol for a coiled Bourdon tube

Diaphragm / Capsule

The marking is not mandatory.
Type of element Symbol
Diaphragm Symbol for a diaphragm pressure element
Capsule Symbol for a capsule pressure element

Maximum steady working pressure

Pressure gauges that can operate continuously at the maximum scale value without compromising the accuracy after a period of time shall be provided with a symbol at the maximum scale value.
The marking is mandatory.

Marking for maximum steady working pressure on the dial of a pressure gauge
Maximum steady working pressure identification mark

The angle of inclination of the dial

When the dial is not vertical but rotated at an angle relative to the horizontal plane, this shall be indicated on the dial. The manufacturer shall then calibrate the pressure gauge in that position.
The marking is mandatory.

Marking for the angle of inclination of the dial
Marking for the angle of inclination of the dial

The calibration temperature

For gauges with accuracy classes [0,1] – [0,25] and [0,6], the calibration temperature shall be indicated on the dial if it differs from the reference temperature. The reference temperature is 20°C.
The marking is mandatory but not for all accuracy classes.

The state of aggregation of the process medium

Bourdon tube

For gauges with accuracy classes [0,1] – [0,25] and [0,6] where the accuracy is only achieved for either gas (G) or liquid (F), this shall be marked on the dial. The use of the abbreviations G and F is not mandatory. The term “calibrated for gas” or the indication of the name of the process medium is also allowed.
The marking is mandatory but not for all accuracy classes.

Diaphragm / Capsule

The indication on the dial of the state of aggregation is not covered by the EN 837-3.
The marking is not mandatory.

datasheets

The number of the followed standard

On the dial can be indicated whether the EN 837-1, if not the EN 837-3 is followed. When EN 837-1 is marked, you know instantly that it is a Bourdon tube. When the marking is EN 837-3, it can be a diaphragm or a capsule pressure gauge.
The marking is not mandatory.

The name of the manufacturer

To easily retrieve the manufacturer or supplier of the gauge, the name or logo of the manufacturer and/or supplier shall be marked.
The marking is mandatory.

The serial number of the device

Bourdon tube

For gauges with accuracy classes [0,1] and [0,25] the serial number must be marked. For the less accurate gauges, classes [0,6] to [4], this is not mandatory. When the pressure gauge is used for metrological purposes, the serial number is mandatory.
The marking is mandatory but not for all accuracy classes.

Diaphragm / Capsule

Pressure gauges used for metrological purposes shall have a serial number. For all other gauges this is not an obligation.
The marking is only mandatory for metrology.

The material of wetted parts

If the wetted parts are not made of brass, bronze, tin or hard solder, their material may be indicated on the dial.
The marking is not mandatory.

Safety pattern gauges

Bourdon tube

The marking S or S-mark for safety pressure gauges together with the EN number, can be applied on the dial of safety pattern gauges, for:

The marking is mandatory but not for all sizes.

Diaphragm / Capsule

The indication of a safety pattern on the dial is not covered by the EN 837-3.
The marking is not mandatory.

Process medium: oxygen or acetylene

Bourdon tube

If the pressure gauge is used for measuring the pressure of oxygen or acetylene, respectively the word “oxygen” or “acetylene”, obligatory written in English, shall be marked. Since oil and grease can ignite spontaneously in contact with oxygen, also the symbol for “no lubrication” shall be marked.

No lubrication mark

Diaphragm / Capsule

The indication on the dial for oxygen or acetylene as a process medium is not covered by the EN 837-3.
The marking is not mandatory.

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