How to calibrate the Pressure gauge

If you have an inexpensive gauge an merely want it to start from zero you might remove the clear face cover pull the needle which is held on by friction strait off. Reposition the needle and press it back on the stem.

I do not think you can change the span on a bourdon tube gauge.

If it is a more expensive (e.g. test gauge) you might try sending it back to the factory.

Finally, you might donate it to a local school and buy a digital electronic gauge in the pressure range you require. Many of these have limited adjust-ability.

Thank you Tom for your valuable suggestions

Ya i did it by adjusting the pointer position on the face and also by adjusting the lever arm..

Tom's right but if you are willing to risk potentially damaging the gauge, you can try.

Zeroing is done by repositioning the needle. You pop it off, position it, then push it back in. You might have to do it several times since you're still learning. Occasionally, zeroing is all that's needed. If the reading is still wrong...

Span is done by adjusting a lever arm that is connected from the center of the gauge to the bourdon tube (the C-shaped thing). Some gauges have the adjustment (you're in luck), some don't (you're out of luck).

Here's something I learned in one seminar I attended. Gauges are supposedly calibrated to be accurate only on the middle third of the range. If the gauge is, say, from 0 to 6 bars, the gauge is calibrated from 2 to 4 bars. What this means is, if the gauge is not zeroed, it doesn't mean that the gauge is inaccurate.

Here's the reason for that. Gauges are usually intended to measure a static pressure (say compressed air at 6 bars). That being the case, you only a gauge that can read 12 bars and the gauge needs to be accurate only between 4 and 8 bars. If the pressure goes below 4 bars, you won't need the accuracy since your system will have shut down due to the low pressure.

Another reason is because of non-linearity. Linear gauges are supposedly difficult to manufacture. To make a gauge linear, you'd need another adjustment for the middle of the measurement range in addition to the zero and span.

Hi gunace, Vulcan, chittaranjan & others,

First since this is gunace's first post welcome to CR4, I hope you get as much out of it a I.

"Here's something I learned in one seminar I attended. Gauges are supposedly calibrated to be accurate only on the middle third of the range. If the gauge is, say, from 0 to 6 bars, the gauge is calibrated from 2 to 4 bars. What this means is, if the gauge is not zeroed, it doesn't mean that the gauge is inaccurate."

Whilst it is true, that when calibrating an aneroid type gauge, you will calibrate the gain¹ at mid range, it dose not necessarily mean that the gauge is not accurate over the whole range that it can display. Cheap gauges will certainly not give you a linear response but this can be accounted for in several ways.

· Non linear pivot systems where the length of the pivot arm varies over the range of the meter

· Non linear scale on the face of the gauge

· Specially designed aneroid chambers that give linear expansion over the range required.

"pressure gauges are calibrated by dead-weight calibrating machine. briefly putting in a nutshel, this has dead weights on one side and pressure gauge mounting on the other side, linked by a pipe/tube having suitable control valve in between and hydraulic fluid filled-in."

This is one method, another is as Shyam suggested the use of a column of liquid like water or mercury. If you are calibrating medical gauges you would normally calibrate them against a column of mercury.

In reality most gauges are calibrated against another, highly accurate, aneroid gauge that is kept as a standard. The intended use will dictate the method and scale that is used for calibration of the standard gauge.

When calibrating an aneroid gauge, it is normal to calibrate the gain first then zero the gauge second. This is because the calibration of the gain affects the zero calibration. Depending on the quality of the gauge and degree of accuracy required you may need to repeat the two calibrations several times as in some gauges the zeroing process will also affect the gain calibration.

Note 1: Gain is the technical term that is used to describe how far the needle deflects over a given increase in pressure. It is sometimes referred to as range or scale.

Thank You Vulcan & Masu

pressure gauges are calibrated by dead-weight calibrating machine. briefly putting in a nutshel, this has dead weights on one side and pressure gauge mounting on the other side, linked by a pipe/tube having suitable control valve in between and hydraulic fluid filled-in.

the procedure here is to put the dead weight required on one side and read the gauge reading corresponding to it. if there is a difference between the dial-reading and dead weight selected, that is the deviation or correction value you have to add or substract when one uses the pressure gauge in question for testing in lab. or for site application. you may approach the manufacturer of the said calibration equipment for in-depth understanding from them.

Bear in mind that even a dead-weight tester has limits. At super-high accuracy requirements, an allowance needs to be made for the buoyancy of the weight in air (as it displaces its own volume of air, which has weight) and the lack of buoyancy of the same weight in a vacuum.

The difference in accuracy between the two situations is say 7000kg/m3 (for cast iron) / 1.2kg/m3 (for air) or about 0.02%.

I think you will find they are all calibrated for sea level, And gravitational variations would have more anomalies than air density which is extremely small.

sir,

i want which iso code use in this calibrating system

If your pressure gauge is meant for fluids, then use a water column as that will give standard pressure for a place.

Here's calibration instructions for one particular brand or model of Bourdon Tube but I suspect that the principals might be similar to the one you have.

http://ittc.sname.org/2002_recomm_proc/7.6-02-12.pdf

thanks for this PDF.but i want know abaut the cause of return error.

Borden tube gauges are designed for a specific span and should not be changed.

Calibration of low pressure gauges can be done with water or mercury columns.

There are many considerations depending on working pressure/ vacuum?? tube design etc. Generally small high press gauges are more rugged but less accurate and are not linearly precise, small low press gauges are delicate and re zeroing needs to be balanced against the return spring operation.

Large diameter gauges are expected to indicate correct pressures over the whole scale range and should be calibrated against a dead weight tester

The best solution is to calibrate your gauge against a reference gauge. Once you have done this, draw up a new gauge face and stick it over the old face. As long as your gauge mechanism is of good quality it will be as accurate as your going to get. Cheers!!

Hello Friends,

I would like to Thank you all for your valuable suggestions and ideas to calibrate the gauge.

Its very helpful for me to do so..

Each & every suggestions gave me some innovative ideas..

Thanks a Lot Friends

In reply to If you have an inexpensive gauge an merely want it to start from zero you might remove the clear face cover pull the needle which is held on by friction strait off. Reposition the needle and press it back on the stem.

Upon reading your thread I tried setting the zero of a Marsh gauge by simply pulling the needle. However, it did come off alone but also broke off the shaft with it. Now the gauge is ruined. My attempt was to use my pocket knife to try to pry the needle off. I assume that it would have worked better to pull it straight off without prying it from one side. Is there some tool or recommended procedure for prying off a gauge needle without also breaking off the shaft?

Sorry about that. 'Should've provided some sort of tool for doing pulling the needle.

This is what we use. We fabricated it ourselves using an small aluminum channel. You still need to exercise some care in using it but it's much better than forcing the needle off with a pen knife.

Note: for putting the needle back, we just push it in.

Ya definitely my friend, what vulcan say is correct...

For that we need a special puller which is available in market also...

Hey guys I'm a student now I'm about graduate from my school and now I'm writing my final report so my I ask U little request

I wanna see schmatic diagrams of pressure gauges bourden tube type

& I wanna these diagrams show all PG parts and components?

Dear Guest,

May I suggest doing an internet search but for Bourdon Tube rather than bourden tube pressure gauges.

This link will take you to the Wikipedia article on Pressure Measurement that has some information about Bourdon Tube Pressure Gauges.

This is the puller I made out of an aluminum wall shelf mount. It is about 1/2" square. I used it to pull the pointer off a 2.25" submersible pressure gauge for scuba. I had to file the screw tip to a cylinder the same diameter as the gauge shaft. It worked fine.