What is Acceptable Percentage of Error for a Guage
- Thread starter Impact701
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Did they say +/-10% of span or +/-10% of indicated?
If this is an ASME Commercial Class D gauge, then it is supposed to be accurate to +/-5% of span over its entire range. Which for a gauge with a span of 0 to 300 bar would be +/-15 bar (+/-217.557 psig). User parallax and needle width on a gauge face with no mirror overlay could add another +/-5%. As such a reading could be +/-10% of range or +/-30 bar or +/- 435.113 psig.
In the nuke submarine navy we had a saying for anything "Nuclear Grade", including our instrumentation, for why it cost so, so, so much more - Measure to 4 atom thicknesses, mark it with chalk, cut it with a chainsaw.
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Prior to retirement I worked with gauges a lot. Your basic off the shelf gauge is accurate to + - 10% of the full scale. Yes that is a little scary and the vast bulk of them or more like 2-3 % however the folks that made the gauge 10% + - is acceptable.
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My rule of thumb for any measuring device is 5% or less error. Most of the time it’s probably not a problem but the one time it becomes a problem once too often. When you’re looking at air pressure it can be catastrophic and not just in terms of damaged equipment but personal injury. 10% is acceptable? I’m calling bulls&*t on that.
Rick H.
Rick H.
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20 bar high, all the time? i.e. when empty at ocean level it reads 21 bar?
If it's always off by 20 bar, you could just rotate the backing screen for the gauge. But that would require opening it up.
If it's always off by 20 bar, you could just rotate the backing screen for the gauge. But that would require opening it up.
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Is the gauge at least consistent in its 20 bar too high reading at whatever pressure? A little sharpie editing of the scale/face might be easier than returning it. And note to all that the brand isn't accurate, thanks.
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My DRS fills to 230 bar, 230 bar reads 250 bar so that is what I have been using. It seams to consistently read 20 bar high.
The gauge that FX put on my DRS is completely unreliable, it never reads the same when its filled to 230 bar.
Must be a Swedish gauge thing ???
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1. If the gauge is analogue - the next time you have degassed the gun, thump the side of the gauge housing using your thumb and forefinger. If the needle jumps, then the connection between the bourdan tube and the indicator movement is bad.
2. If the gauge is digital - slowly degass the gun and check that the indicated pressure decreases linearly and doesn't fluctuate up and down. Do the same when you slowly pressurize the gun.
If it does fluctuate -
1. Check that the battery has not leaked.
2. Change the battery, ensuring the connections are clean.
3. Retest
4. If the indication still fluctuates, then the circuit card or piezo-resistor is bad, and you need a new gauge.
2. If the gauge is digital - slowly degass the gun and check that the indicated pressure decreases linearly and doesn't fluctuate up and down. Do the same when you slowly pressurize the gun.
If it does fluctuate -
1. Check that the battery has not leaked.
2. Change the battery, ensuring the connections are clean.
3. Retest
4. If the indication still fluctuates, then the circuit card or piezo-resistor is bad, and you need a new gauge.
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Also note that the air temperature will impact the pressure, both gauges and air should be at the same temperature for a valid comparison.
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I just found this thread while running into a situation with gauges myself.
First, some background, I've never had what you call really accurate gauges. In one sense, what is a "really accurate" gauge?...any gauge can be off, even a really good one. So, normally, if my gauges on my compressor, and guns,(many guns) are in relative agreement, then I feel safe.
I have a used Sekhemt gauge that consistently reads well off any other gauge I've had, including many, many pcp airguns. It is on the order of 16 bar off as near as I can tell. It's one of the newer Sekhmet gauges, but it doesn't match anything I've had. UNTIL, I got a Dream Tac with Wika gauges, and I discovered, the Sekhmet reads exactly with both Wika gauges. This got me thinking and I ordered one of Huma's digital reg testing gauges, and sure enough, the Sekhmet, Wika and Huma all read the same. Guess I was wrong about the Sekhment.
Now let's consider gauge error. When scuba tanks or breathing air cyls are filled, they allow a 10% overfill for heat. So on a 4500psi CF tank that's 450psi overfill. A gauge error like mine of something on the order of 16 bar is less than 250 psi and on a 230 bar gun like the DreamTac that would be a roughly 10% overfill.
Cylinders, of any material, be it aluminum or carbon fiber are overbuilt to the max. I can't remember aluminum but CF cyls are burst rated at north of 17,000 psi for scba, IIRC. That's better than a 3:1 safety factor. Also remember that a smaller diameter will hold a higher pressure.. Let's face it NO manufacturer wants to deal with a bottle explosion situation. Kinda hurts business to the extreme. That's not to say we shouldn't pay attention, it just means we should be aware. Did you know in the US any cyl 2" and under in diameter doesn't need to be retested....ever. That's because the likelyhood of an explosion is quite small. I saw the numbers once and it was something like many hundreds of thousands of fill/drain cycles to reach a stress fracture at the relatively low force loading. That is the reason you don't see 4500 psi aluminum cyls, it is to keep the failure rate so far out that it is, fall all intents and purposes, nearly impossible.
Now, for common sense. I almost never fill my guns to max. I don't need to, I have a ready air compressor wherever I shoot, so a few extra shots before a fill isn't of any concern to me. If the situation arises that I need max shot count, I'll fill to max. I think the only time I've ever filled guns to max was to see if the reg acted any different with more pressure in the cyl.
So a combination of being aware of the situation, not going crazy filling, and keeping an eye on gauges, you should be perfectly safe.
First, some background, I've never had what you call really accurate gauges. In one sense, what is a "really accurate" gauge?...any gauge can be off, even a really good one. So, normally, if my gauges on my compressor, and guns,(many guns) are in relative agreement, then I feel safe.
I have a used Sekhemt gauge that consistently reads well off any other gauge I've had, including many, many pcp airguns. It is on the order of 16 bar off as near as I can tell. It's one of the newer Sekhmet gauges, but it doesn't match anything I've had. UNTIL, I got a Dream Tac with Wika gauges, and I discovered, the Sekhmet reads exactly with both Wika gauges. This got me thinking and I ordered one of Huma's digital reg testing gauges, and sure enough, the Sekhmet, Wika and Huma all read the same. Guess I was wrong about the Sekhment.
Now let's consider gauge error. When scuba tanks or breathing air cyls are filled, they allow a 10% overfill for heat. So on a 4500psi CF tank that's 450psi overfill. A gauge error like mine of something on the order of 16 bar is less than 250 psi and on a 230 bar gun like the DreamTac that would be a roughly 10% overfill.
Cylinders, of any material, be it aluminum or carbon fiber are overbuilt to the max. I can't remember aluminum but CF cyls are burst rated at north of 17,000 psi for scba, IIRC. That's better than a 3:1 safety factor. Also remember that a smaller diameter will hold a higher pressure.. Let's face it NO manufacturer wants to deal with a bottle explosion situation. Kinda hurts business to the extreme. That's not to say we shouldn't pay attention, it just means we should be aware. Did you know in the US any cyl 2" and under in diameter doesn't need to be retested....ever. That's because the likelyhood of an explosion is quite small. I saw the numbers once and it was something like many hundreds of thousands of fill/drain cycles to reach a stress fracture at the relatively low force loading. That is the reason you don't see 4500 psi aluminum cyls, it is to keep the failure rate so far out that it is, fall all intents and purposes, nearly impossible.
Now, for common sense. I almost never fill my guns to max. I don't need to, I have a ready air compressor wherever I shoot, so a few extra shots before a fill isn't of any concern to me. If the situation arises that I need max shot count, I'll fill to max. I think the only time I've ever filled guns to max was to see if the reg acted any different with more pressure in the cyl.
So a combination of being aware of the situation, not going crazy filling, and keeping an eye on gauges, you should be perfectly safe.
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200 or 300 bar? - International Diving Federation
Are cylinders that are filled to 300 bar a better solution than the standard 200 bar? This article will try to answer this question.
idf-global.com Interesting read on the reduced amount of air per bar one gets charging above 230 bar anyway.
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I admit I can get anal about gauges not reading the true measure. I like my BMW, for instance, but BMW purposely has the speedometer programmed to read 5 km/hr faster than the car is going. I activiated a little digital speed indicator that the M cars come with and was able to remove the "correction" factor on it but from what I read on-line nobody has managed to defeat the false reading on the main speedometer. To me doing it deliberately is worse that an unintentional error in the gauge.
For my PCPs, I have a good fill set (from Joe Brancattos company) with a gel filled gauge that is large enough to see. It seems to agree with the little gauges on my guns. So I use the gauge on the fill set when filling my guns and also when refilling my bottle. The gauge on the Yong Heng does not even work now but I don't care, I wouldn't use it if it did work. My point is just that it matters a lot more if the gauge in question is one you will use. If it is, then I might send it back. But if it is just a gauge you might occasionally look at but wouldn't use for anything critical, I think I would live with it.
For my PCPs, I have a good fill set (from Joe Brancattos company) with a gel filled gauge that is large enough to see. It seems to agree with the little gauges on my guns. So I use the gauge on the fill set when filling my guns and also when refilling my bottle. The gauge on the Yong Heng does not even work now but I don't care, I wouldn't use it if it did work. My point is just that it matters a lot more if the gauge in question is one you will use. If it is, then I might send it back. But if it is just a gauge you might occasionally look at but wouldn't use for anything critical, I think I would live with it.
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