Looking for calibration specification for Fluke 7250 pressure controller

[Rmack]

EDIT: Sorry, something changed the message title I originally posted. I'm not looking for specs, I know where those are. What I'm looking for is discussion on what part of the spec you would use in this situation to determine the tolerances to put in a calibration procedure.

I’m trying to write a calibration procedure for a Fluke 7250 pressure controller and their jumble of specs has me a bit confused.

According to the sales guys the precision is 0.005% reading.

Calibration tolerance in their documentation is 0.009% of reading where accuracy is defined as the maximum deviation from the value of pressure including precision, stability, temperature effects, and the calibration standard.

It seems to me that stability, temperature effects, and the calibration standard would certainly effect the uncertainty of the measurement but don’t belong in the calibration limits column of the cal procedure. That in order for it to achieve the 0.009% accuracy spec it would need to agree with the standard within the 0.005% of reading precision at calibration time.

Their method appears to compare the 7250 to the standard and call it good if it is within 0.009% of reading. This seems inflated to me and would result in even poorer instrument performance when stability and temperature effects would be different from conditions at calibration time.

When you write a procedure which spec would you use?

 

[dgriffith]

Have you tried the Fluke website http://us.flukecal.com/products/pressure-calibration/automated-pressure-controllercalibrators/7250-series-pressure-controll?quicktabs_product_details=1 for the 7250. Contains spec info and a few examples describing what they mean.
We calibrate our 7750i, 7010-1 and 7010-10 controllers; when I get a chance I'll post about it.

I would use the precision value 0.005%rdg as the performance limits for calibration (tolerance).

The total uncertainty values are what you would use when the controller is the reference for another UUT. They mention control stability separate from the total. I would include it additonally if controlling instead of just measuring.
Your standard would have to be a suitable substitute for theirs to keep the 0.009% total uncertainty valid.

Edit to your edit: I look at it like this: The 0.005% rdg precision is the measurement performance tolerance. As a measurement instrument, it will meet that limit with the appropriate calibration reference standard, and of course during calibration it is in measurement mode. This is the intrinsic capability, so to speak.

When a controller controls, it is measuring its own pressure; it develops an error signal that controls the valves, etc. etc. to cause the target pressure and measured pressure to be equal (electrically/digitally). Valve control and other influences cause the performance limits (in control mode) to increase, say 0.009%rdg.

So, 0.005% to calibrate it, 0.009% when you use it.

 

[Rmack]

Dgriffith,

Your description really clears it up. Red stuff and blue stuff I'll gladly read it all.

Thank you!

RMack

 

[Slammy]

Quick Question: Which organization do you feel should oversee Calibration and Metrology.. Manufacturing Engineering or QA?

 

[dgriffith]

There is no set 'department'. It might depend on the company, their willingness to bring in a qualified person(s), or who has the most experience within the company.
NASA Metrology is under Safety and Mission Assurance (SMA) at the agency level, but at the individual Centers you will find Metrology under Research, Flight Operations, SMA, QA and many others.
No rule, though many private companies have it under some Quality function (because they're the experts in all things quality, don'tcha know... ).

 

[Rmack]

It really depends on the place but it's very important that the calibration functions are allowed to operate without undue pressure to provide results that are "convenient". In my experience that's more likely to happen with metrology aligned under quality assurance.