Can you trust an analog pressure gauge?
Can you trust an analog pressure gauge?
(OP)
Can you trust an analog (dial, needle) pressure gauge, even one that is oil filled?
I went to a seminar this week on improving cutting in sawmills and one of the speakers strongly suggested that you switch from analog gauges to digital gauges for air pressure. He said he’d seen failure rates as high as 50% on the analog gauges.
He brought up two particular failure modes. One was that the needle was just pinned on and that the needle could shift with enough bouncing. In addition he said that these gauges were only really accurate in the middle of their range so they were not at all satisfactory if you are trying to keep 10 pounds of pressure with a 0 to 100 PSI gauge.
In his experience he has seen a production lines where five out of 10 gauges were bad. He talked about a troubleshooting situation where he replaced 10 gauges and five days later three of them were bad.
This guy is a mechanical engineer from a well - respected company and he said his company has done a great deal of testing and gauges has not been able to find a satisfactory analog gauge.
His examples were all in sawmills, specifically in use in log handling equipment. There is a great deal of vibration in everything while the line is running.
My question is whether these analog pressure gauges are suitable for use in any application?
Thanks,
Tom
I went to a seminar this week on improving cutting in sawmills and one of the speakers strongly suggested that you switch from analog gauges to digital gauges for air pressure. He said he’d seen failure rates as high as 50% on the analog gauges.
He brought up two particular failure modes. One was that the needle was just pinned on and that the needle could shift with enough bouncing. In addition he said that these gauges were only really accurate in the middle of their range so they were not at all satisfactory if you are trying to keep 10 pounds of pressure with a 0 to 100 PSI gauge.
In his experience he has seen a production lines where five out of 10 gauges were bad. He talked about a troubleshooting situation where he replaced 10 gauges and five days later three of them were bad.
This guy is a mechanical engineer from a well - respected company and he said his company has done a great deal of testing and gauges has not been able to find a satisfactory analog gauge.
His examples were all in sawmills, specifically in use in log handling equipment. There is a great deal of vibration in everything while the line is running.
My question is whether these analog pressure gauges are suitable for use in any application?
Thanks,
Tom
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
Good engineering starts with a Grainger Catalog.





RE: Can you trust an analog pressure gauge?
I think that for general use, i.e., for non-critical accuracy applications, it's OK. We use pressure gauges for cryogenic gases, but we don't necessarily care if the reading is 20% off.
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RE: Can you trust an analog pressure gauge?
RE: Can you trust an analog pressure gauge?
Industrial quality gages are not cheap. You will not find them at the Home Depot or even most industrial supply stores unless these stores sell to chemical plants. Chemical plants are loaded with analog pressure gages and these gages are quite reliable. Tapping them is still a good practice, though. The tapping simply verifies that the linkages in the gage are not stuck or disconnected, in which case the gage is very likely to be reading correctly.
RE: Can you trust an analog pressure gauge?
1. only between 20% and 80% of full scale
2. check calibrations (removed from system) regularly (depending on service, usually 3 months)
3. they are $400 gages, not $7.\
The only draw back to digital is the zero drift. We often find zero off by 10psi.
But if they give you a reading they are working, if they break you get nothing, not a wrong value.
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
RE: Can you trust an analog pressure gauge?
There are clear advantages to digital gauges, but as has been pointed out, many of these have nothing to do with being analog or digital, but, rather, of gauge conctruction quality. If fact, a digital pressure gauge is a specialized form of an analog gauge, the only difference is the output signal is digitized prior to display. It is still using an analog relationship between the pressure and the output.
In the seminar speaker's experience, the cautionary recommendation against is probably appropiate for applicaitons for which the speker has experience. To say this applies to all applications is a pretty broad extrapolation. This is like saying digital calipers should always be used over dial calipers (or even vernier calipers). While in many applicaitons, digital calipers do well, but I have seen cheap digital calipers I would not trust and, while a vernier caliper can be difficult to learn how to use, there are applicaitons where they would be preferred.
rp
RE: Can you trust an analog pressure gauge?
I think a purely digital tachometer would be of little use for anything but top speed runs.
http://www.youtube.com/watch?v=-6j3glUtecY
RE: Can you trust an analog pressure gauge?
RE: Can you trust an analog pressure gauge?
The precision of an analog dial measurement is visually apparent merely by looking at the gauge- particularly when the measurement is fluctuating.
If you buy decent bourdon-tube gauges, install snubbers and/or oil fill them when they're in vibrating service etc., they can be reasonably accurate and last a long time. But they are definitely susceptible to damage from vibration, overpressure, or especially when people use the case rather than a wrench to install them.
Good quality industrial pressure transmitters should hold their zero value stable for a long time. The cheap piezoresistive ones that are often used in "digital gauges" are another matter entirely- they vary greatly in quality, durability etc. and there are probably a hundred brands on the market.
Mechanical differential pressure gauges on the other hand are not my favourite. And the zero of most industrial differential pressure transmitters shifts significantly with changing common-mode pressure. Yokogawa and ABB now have technology in their DP transmitters which can null out that effect very well, and also give you the gauge pressure at the + or - leg as a 2nd output over HART etc. Rosemount hasn't caught up with that yet.