# Calibration and Tolerance Ranges of Pressure Gages

#### dwhite624

##### Starting to get Involved
We have a new testing facility in our shop which uses many different pressure gages to measure various gasses and air pressures. The person who did the calibration did not have tolerance ranges on his certs and I was curious if we:

1. Need them on the certs?
2. If so, what is a standard rule of thumb when it comes to pressure gage tolerances for calibration (i.e. -.00004 / -.00001 for Deltronics Pins)?

#### Kales Veggie

##### People: The Vital Few
I have a couple of questions:

1) do the gages have to be calibrated? (...to ensure valid results...)
2) rule of thumb is a factor of 10 between calibration tolerance and the resolution you need for your test / measurement.

#### dwhite624

##### Starting to get Involved
Thank you for your quick response.

1. Yes, the gages do have to be calibrated. There are many gages in the system but only a few are actually measuring critical pressure. These are the gages that need calibration.

2. I am thinking about just using the rule of +/- 1/2 the smallest increment on the gage.

Any thoughts on this?

#### Ninja

##### Looking for Reality
Trusted Information Resource
What happens when the smallest increment on the gage is larger than your process needs?

That's why you should base your calibration off of the process need...

the gage doesn't need the calibration, it won't care.
It is the process that needs the gage to be accurate.

S

#### sandore

pressure gauges have categories named Class, it's at front of them like Kl 1.0; CL 2.0. Each class means a error tolerance of the full range, example class 1.0 of a gauge range 100 psi means the maximum error 1% of 100 psi = -/+ 1 psi. calibrating the gauge error is found and the gauge satisfied if the error is at or below the class.

Class of manometers are
0.1% for standard gauges
0.2%
0.3%
0.6%
1.0% for process needed of good precision
1.6%
2.5%
4.0% the most of industrial gauges

One more thing: standard gauge to calibrate should have a better class of gauge to be tested, preferably, where possible, a 4:1 ratio and standard range the must be equal or maximum twice.

I hope that helps a little.

Last edited by a moderator:

#### dwhite624

##### Starting to get Involved
Thanks for the knowledge Sandore. That's exactly what I was looking for.

F

#### fast_hedgehog

We use this for all bourdon tube gauges:

BS EN 837-1:1998

Pressure gauges. Bourdon tube pressure gauges. Dimensions, metrology, requirements and testing

Status : Current Published : March 1998

It includes the classes mentioned already.

#### Charles Wathen

##### Involved - Posts
pressure gauges have categories named Class, it's at front of them like Kl 1.0; CL 2.0. Each class means a error tolerance of the full range, example class 1.0 of a gauge range 100 psi means the maximum error 1% of 100 psi = -/+ 1 psi. calibrating the gauge error is found and the gauge satisfied if the error is at or below the class.

Class of manometers are
0.1% for standard gauges
0.2%
0.3%
0.6%
1.0% for process needed of good precision
1.6%
2.5%
4.0% the most of industrial gauges

One more thing: standard gauge to calibrate should have a better class of gauge to be tested, preferably, where possible, a 4:1 ratio and standard range the must be equal or maximum twice.

I hope that helps a little.
Great info. Also note that some pressure gauges may have a tolerance of 3-2-3% FS.

S

#### sandore

Good morning, Charles.
Sorry for the lateness of the response.

In bourdon tube pressure gauges at the beginning and end of the range of the cover often have errors, hence these tolerances. In such cases the more tolerant classifies gauge. In the center the error is smaller, so the choice of a gauge of this type must be remembered that. Find that reading interest is in the central part of the manometer.

Best regards

Sandore

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