Calibrating a pressure gauge

[cheb]

Firstly, this isn't a particularly serious request, I'm too mean to lump out £100+ for a calibrated gauge and more that I wonder if there's a way of checking a gauge's accuracy at home. The same level of simplicity as checking a torque wrench with some known weights and a bit of calculation.

How about connecting a small brake master cylinder so that it vertically pushes a known weight of water? Calculate the area of the master cylinder and with a bit of maths you've got the pressure in the system.

 

[scottmk1]

If you have a couple more pressure gauges of similar range connect them all into your system and see if they all read the same. If yes it’s quite a good way to check.

 

[cheb]

But that only tells me if they are consistent, not if they are correct.

 

[daleyd]

Even if you were smarter than me and did the maths etc - how would you know what you've got coming out the end is actually 100% correct though? (losses through system, compressibility - no idea if any of that is realistically going to affect anything to a great degree but you could never be absolutely sure)

If you are that concerned the only way I would think is to get a calibrated gauge and compare.

 

[scottmk1]

The idea is that what’s the chances of them all reading incorrectly, by the same amount.

Just like your idea should work but the results are only as accurate as the test circumstances allow for.

 

[Maker]

How about connecting a small brake master cylinder so that it vertically pushes a known weight of water? Calculate the area of the master cylinder and with a bit of maths you've got the pressure in the system.

That's how dead weight testers work, Budenberg make them, you might find a cheap one if you're made of luck.

I don't know how you'd stop static friction in the piston from influencing the calibration, and you can only be as accurate as your weights, have you got calibrated weights? Compressibility won't be an issue but you will need to consider things like the piston needing to be absolutely vertical.

EDIT:
Here's a training video from Budenberg, at 3:45 they say when the approximate desired pressure is reached, the weights should be rotated, I'd imagine that's how they get past the static friction problem.

 

[anto44]

Depending how accurate you want to go you're going to have to account for the friction of the seal in the master cylinder. Those seals are pushed against the cylinder wall by the pressure in the cylinder, the higher the pressure the harder the seals are pressed against the wall and the more friction generated.
A hydraulic cylinder with an oring seal might work better

 

[fizzy]

If you have a few accurate tyre pressure gauges you could connect it to a car tyre to check.

 

[Neilj]

What's the range of the pressure gauge you want to check?

 

[Misterg]

I don't know how you'd stop static friction in the piston from influencing the calibration,

As you've sussed, they spin them around.

I was on a placement with some instrument engineers at BP in Dyce and went with one of them to see the bloke that calibrated their DP gauges (looking for a few milliBars pressure difference in several thousand Bar static). He was an ex diver with a really hoarse, whispy voice and he had one of those Budenberg gauges set up in a lab behind his house.

As well as all sorts of accurate weights, he also had a measurement of gravity at his exact location to use in the calculations.

(Sorry for the hijack!)

 

[zzr1200]

So you want/need a certified gauge. What process/job and why do you need to know an accurate pressure, +/-tollerance???

......an explanation of the requirement would help no end.....

 

[brightspark]

But that only tells me if they are consistent, not if they are correct.

whats so important that it needs to be 100 percent accurate

 

[Pete.]

But that only tells me if they are consistent, not if they are correct.

Well yes but what are the odds that three gauges will read false by exactly the same amount?

 

[brightspark]

Well yes but what are the odds that three gauges will read false by exactly the same amount?

and if any of them were out from new they would soon be in bother selling them

 

[anto44]

I've had pressure gauges tested calibrated in work by a specialist calibration company and all they did was compared it to their digital gauge which we were told was calibrated by someone else.
If you don't need all the paperwork and just want to reassure yourself that your equipment was accurate then you could see if anyone here has a calibrated gauge of the right pressure range and do a comparison test. Connect them both to a T-piece supplied with pressure and see do they match through the range.

 

[Ross365]

If you have a couple more pressure gauges of similar range connect them all into your system and see if they all read the same. If yes it’s quite a good way to check.

Checking "out of three" is generally quite useful. I never bought calibrated gauges; too expensive. But I did buy one gauge, had that calibrated locally (not very expensive) and then kept that to one side (my "Master Gauge")- never using it for any general usage, but only taking it out of its box when I wanted to check other gauges.

Of course, everything depends of the standard of accuracy that you are after. More accuracy and more verification - more cost.

 

[daleyd]

Checking "out of three" is generally quite useful. I never bought calibrated gauges; too expensive. But I did buy one gauge, had that calibrated locally (not very expensive) and then kept that to one side (my "Master Gauge")- never using it for any general usage, but only taking it out of its box when I wanted to check other gauges.

Of course, everything depends of the standard of accuracy that you are after. More accuracy and more verification - more cost.

That’s exactly the way any calibration works, in principle. The company I work for do a lot of calibration services for customers (not something I tend to get involved with as it’s not my dept) but basically everything is calibrated against a known standard, which itself will be calibrated against another, usually higher quality one, and so on and so on…

The standard our guys use to calibrate their instruments against has to be kept in a temperature/humidity controlled lab - I assume the one that is calibrated against is kept to even higher environmental standards etc etc

 

[doubleboost]

The bit you want is 11 minutes in

 

[Chippie]

I used to work at a gas terminal on the east coast as an instrument technician initially before aspiring to the dizzy heights of engineer; in our workshop we had several Budenberg dwt’s for testing gauges dotted around the plant and for calibrating pressure transmitters…One other thing we did was recertify ‘Standard‘ test gauges ( including a calibration sheet detailing any error) for the Mech dept. where they used the gauges for pop testing relief valves….and other jobs requiring accuracy. When not in use, the gauges were kept in a cupboard.
Certifying gauges was just one job we had, we had gas metering systems that had to be calibrated and certified to fiscal standards, often witnessed by a rep from the then Dept of Energy( DEN )…,

To go back to the ops post, check calibrating a gauge can be done using the brake cylinder method… you need to know the force applied ( the mass of the ‘weights’ applied) to the piston and the piston’s area..as a basis …

 

[500e]

The weights and measures inspector used to check the Garage units, normally only the one the public could use, never asked about +- as long as it passed