Gauge and absolute pressure

[captainrabin]

The pressure gauge is calibrated in seal level with standard atmospheric pressure 101325Pa. It shows '0' reading there if not connected to any compressed air.

Do the same pressure gauge shows same '0' reading in another place where the height and atmospheric pressure is different ?

If it is in higher altitude than seal level gauge pressure will show less than 0,and if it is taken to lower altitude than sea level gauge pressure more than 0.
Can the gauge pressure calibrated in USA can be used in India.

Absolute pressure remain same everywhere whereas atmospheric and gauge pressure differs.

Correct me.

 

[IRstuff]

Much depends on whether it behaves like a sealed pressure gauge.

If it's just an electronic offset, then you always measure against the calibrated offset

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[LittleInch]

Well it depends.

"Do the same pressure gauge shows same '0' reading in another place where the height and atmospheric pressure is different ?"
No. That's how a lot of altimeters work (air pressure).
A personal tale here: I used to jump out of airplanes for fun. You always had to zero your altimter each weekend as the weather changed or you went somewhere different. One day we set off from an airfield to jump into a vineyard about 30 miles away. We asked what the altitude was at the landing point and were told "It's all flat round here". We were the first lift. WRONG. Given you normally open at 2000 to 2500 ft it was rather interesting to say the least when we discovered after landing that the ground was 700ft HIGHER.

So the next lift set their altimeters / pressure guages at -700 ft at their ground level. So in that case pressure really matters.

If it is in higher altitude than seal level gauge pressure will show less than 0,and if it is taken to lower altitude than sea level gauge pressure more than 0.
Correct, but remember that many gauges have a pin which prevents movement below zero on the gauge

Can the gauge pressure calibrated in USA can be used in India.
Of course it can

Absolute pressure remain same everywhere whereas atmospheric and gauge pressure differs.
Correct

However is it important? A 0-16 bar guage say won't vary by more than about 0.3 barg (3,000m elevation). Do it for a 0-1 bar guage and it's a different story.
Many guages have a zero adjustment screw, so just zero it with no internal pressure.
Transmitters either reference the ambient air as a pressure differential or reference against a very high vacuum which is sealed in.


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[crshears]

It depends...

If the pressure gauge is of the type that consists of a Bourdon tube that connects to the measured pressure, and the Bourdon tube connection is not capped off whilst the gauge is at sea level, no pressure differential will develop between the inside and outside of the Bourdon tube and therefore its reading will not change if that gauge is brought to an altitude.

Take that same gauge, cap it off on a very cold day while at sea level, then transport it to an altitude, and the needle may well lift from the zero pin, depending on the gauge's pressure measurement range; the lowering of the external pressure develops a pressure differential between the inside and outside of the Bourdon tube.

Altimeters function on the same principle, viz., comparing external [atmospheric] pressure to that within a sealed reference pressure cell. They are however far more sensitive than the crude sealed pressure gauge as described, and as LittleInch has elaborated on can be readily calibrated to the prevailing local atmospheric pressure so as to give accurate readings of elevation above sea level.

CR

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[Compositepro]

Standard pressure gauges are actually differential pressure gauges that measure the difference in pressure between the sensor port and the surrounding atmosphere. An absolute pressure gauge differs in that it contains a sealed chamber that has been evacuated to a near perfect vacuum, and it measures the pressure difference between the sensor port and this sealed reference chamber.

Altimeters are absolute pressure gauges. To calculate altitude from absolute pressure there must be a correction for changes in barometric pressure due to weather.