pressure cal's using deadweights

[skolito]

Here is a question I am researching maybe someone can help.

Say I need to do a pressure module accuracy of ±0.05% of full scale.
My good dead weight (±0.008) is broken and at the mfr. I have aother dead weight of ±0.1% of reading. Can I use it if I have the true pressures at reference gravity of 980.665 and correct for my local gravity of 979.6767?

[OlDave]

Say I need to do a pressure module accuracy of ±0.05% of full scale.
My good dead weight (±0.008) is broken and at the mfr. I have aother dead weight of ±0.1% of reading. Can I use it if I have the true pressures at reference gravity of 980.665 and correct for my local gravity of 979.6767?

I assume you know how to use it, so sure go right ahead.

A better question would be....Would it provide a valid calibration?

Not at MY lab.

In actuality, that ±0.1% of reading is only technically valid at or near standard gravity. You are dealing with piston distortion, drag, cylinder distortion, head pressure, temperature coefficients, etc., etc., that have not been corrected on a low end dead weight tester like that.

[skolito]

I thought the same thing but the mfr of the dead weight said that doing it that way I take the error out because I'm using the "true" pressure readings and then using the formula for my gravity vs. std gravity.
Of course this would be pointless if my good tester didn't shear the piston off and will be gone for 6-8 weeks

[MIRCS]

That's a slippery slope to travel

[flew-da-coup]

I thought the same thing but the mfr of the dead weight said that doing it that way I take the error out because I'm using the "true" pressure readings and then using the formula for my gravity vs. std gravity.
Of course this would be pointless if my good tester didn't shear the piston off and will be gone for 6-8 weeks

You might be able too by working out the actual uncert, but I doubt you will be able to get it that low. I wouldn't recommend using the MFR's suggestion unless you can prove on paper that you are at least getting a 1:1 TUR.

[Hawaii596]

I'll toss some questions out to see who's pretty knowledgeable about such things....

As an electronic ex-Navy pmel type, I've never really used deadweight testers.  I'm pretty good at self-training, so I know I'll find some good info and learn (not to mention my senior tech is ex-Navy, been to the 38 week version of PMEL school at Lowry and a very sharp tech).  But I recently moved back to Texas and into my new position as Sr. Metrologist / QA Supervisor at a lab here.  One of my projects is getting a bunch of stuff on line.  I've found two deadweight testers.  One is an Ametek model PK II 854WC-SS, 4 - 854" H2O range.  It looks in great shape, the weights are shiny, and it has been sitting on a shelf since its last cal in 2001.  I'm going to send it out to get certified and hope to add that to our labs capability.  The other deadweight tester is an old Budenberg.  I've found some Budenberg units on the internet.  But I've yet to identify what model this thing is, and/or any info about it.  We have various weights for it, there is a reference pressure gauge, I think is 0 - 60 PSI (or KPA - don't remember).  The gauge face is about 12 inches in diameter.  There is some sort of control interface, a small grey box with a couple of knobs on the front and some tubing underneath.  Anyone know anything about Budenberg deadweight testers have any clues.

So...  if anyone has any good info about proper use of deadweight testers, or info about old Budenberg units, I'd really appreciate it.  The PKII, by the way, has the original OPERATING INSTRUCTIONS with it, so I do have that.

[Bryan]

It's been over 20 yrs since I used one, the Army at the time had one called a Mansfield Green.
I remember as you added the weights (they were round) speaking in my best Wolfman Jack voice that you had to spin them to minimize friction with the cylinder the piston rode in.
1.  Always ensure pressure is relaesed before removing weights.
2.  Never operate without the safety retaining pin in the piston, see rule 1.

I have forgotten how the amount of weight translated to pressure, was a simple enough formula but many brain cells ago.

[ventura]

The Weights provide a different amount of pressure based upon the orriface that you have installed in the unit. 

For the off brand I am not familiar but I have an Ametek which just so happens to say Mansfield and Green on it too.  It seems that Ametek is a division of Mansfield and Green.

Yes, you spin the weights gently and when you attain that magic floating point you have balanced out the weights with your UUT at that given pressure that the weights are suppose to give you.

As for the OP original question.  No I wouldn't do it.  I think there is to much uncertainty in the measurement process using that type of system for me to put my stamp on it.

[MIRCS]

The Weights provide a different amount of pressure based upon the orriface that you have installed in the unit. 

For the off brand I am not familiar but I have an Ametek which just so happens to say Mansfield and Green on it too.  It seems that Ametek is a division of Mansfield and Green.

Yes, you spin the weights gently and when you attain that magic floating point you have balanced out the weights with your UUT at that given pressure that the weights are suppose to give you.

As for the OP original question.  No I wouldn't do it.  I think there is to much uncertainty in the measurement process using that type of system for me to put my stamp on it.

Just to clarify mansfield&Green are a division of Ametek.

[ventura]

The Weights provide a different amount of pressure based upon the orriface that you have installed in the unit. 

For the off brand I am not familiar but I have an Ametek which just so happens to say Mansfield and Green on it too.  It seems that Ametek is a division of Mansfield and Green.

Yes, you spin the weights gently and when you attain that magic floating point you have balanced out the weights with your UUT at that given pressure that the weights are suppose to give you.

As for the OP original question.  No I wouldn't do it.  I think there is to much uncertainty in the measurement process using that type of system for me to put my stamp on it.

Just to clarify mansfield&Green are a division of Ametek.

Oh Ha Ha...I must have misread the label on my Dead Weight Tester.

:sorry:

[Hawaii596]

I posted a little while back regarding some deadweight testers we have.  We are all metrologists with PMEL school (Navy version for me), but unfortunately mostly electronic background.  We are pulling an inherited old deadweight tester out of mothballs to get it calibrated and online.  It is an Ametek with a nozzle and ceramic ball.  It has a set weights and two different sized sleeves.

I hang one of the sleeves on the ceramic ball with three points contacting the top area of the ball.  I hang weights on the sleeve, and pump up the inlet pressure to the prescribe amount (between 30 and 100 PSIG).  We are not calibrating anything with this yet (still need to send it out to be certified), just learning how to use it.

So here is my dummy question.   We've got a Druck 300 PSIG calibrator with a builtin hand pump that we've connected up to the inlet port of the deadweight tester.  I pump up the deadweight inlet pressure to somewhere around 40 PSIG or so using the Druck connected to the inlet.  The ball definitely appears to float properly.  But even with the outlet port closed off (where we would normally connect the pressure gauge under test), the pressure level in the deadweight tester bleeds down pretty quickly.   In about say 30 - 45 seconds, it bleeds off to nothing.

So, does this mean this system is designed to be connected to a pressure "SOURCE" (not a hand pumped gage, but a bottle of N2 or house air supply), or does it mean that we may have leaks in the deadweight tester (that will hopefully be corrected when we send to OEM for calibration)?

[mdbuike]

It may be time to change the seals..I'd get a hold of Ametek with your model number..we've found them very helpful even when they don't carry the stuff, they'll try to point you towards a vender who does...

But then, why not drop some bucks and get an RPM 3?

I now, you're commercial, but efficiency and accuracy should count for some..

Ah well, it's laser day tomorrow..some "found" fiber optics..I just shake my head

Mike

[OlDave]

So, does this mean this system is designed to be connected to a pressure "SOURCE" (not a hand pumped gage, but a bottle of N2 or house air supply)

Yes, that is the way these work. You need a constant source capable of a little flow connected to the inlet. Your test gage connects to the outlet. When the ball floats your outlet pressure equals the amount shown on the weight stack plus the weight carrier pressure.

I call those things "precision regulators", but they actually work pretty well. I've got one myself. As with all pressure calibrations make sure your setup is leak free. These floating ball testers are a little trickier for that because unlike a regular floating piston dead weight tester that will sink with a leak, these will just keep on floating because the inlet flow will compensate and keep the ball floating even though the pressure is bleeding off downstream before it reaches your gage under test.

[Hawaii596]

Just to continue to make myself sound dumb in this area, I think I interpret correctly that when my pressure source is a handpump (or built in to a Druck pressure calibrator), I can pump up (for example) to 50 PSIG, my ceramic ball will float with the fixture and some weights attached.  But because it is designed based on a very small flow (leak), it will gradually bleed down to zero.  Therefore, in evaluating the operational condition of this deadweight tester, that aspect is considered to be working fine. 

It's been sitting for a number of years.  Long enough that the weights stuck to the dense black foam rubber, and we could see a little very slight discoloration on the part of each weight that was in the foam.  We should probably clean them with Alcohol before sending to the OEM for system cal.

Thanks for the inputs on this.  Please feel free to dump vast quantities of info on this to me.

[OlDave]

It sounds like you have pretty good basic understanding of how they operate.