NIST Traceability: OEM Products - New electronics measurement device

J

joecalibratio

#1
Our company is releasing a new electronics measurement device. Let me know if the following has any traceability gaps. I feel uneasy with this....

1. We are the OEM for item "A" (DUT)
2. Item "A" requires calibration
3. Our engineering dept. designed a calibration device (standard) to calibrate item "A" (DUT)
4. This calibration device (standard) obtains power from item "A" (DUT)
(CAN WE CALIBRATE EQUIPMENT WE MANUFACTURE WITH EQUIPMENT WE MANUFACTURE?)
What does Fluke do?
I value being able to utilize established standards such as oscilloscopes/dmm's/function generators but our engineers are trying to eliminate the need for such. Does the above "plan" fit within NIST Traceability requirements?
Your opinions and comments are extremely welcome!

thanks!
 
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Jerry Eldred

Forum Moderator
Super Moderator
#2
Many instruments have a "SELF CALIBRATION" feature. HOWEVER (and it is a BIG however), this is not a substitute for a NIST traceable calibration. The Agilent (HP) 3458A for example, has an AUTOCAL feature which linearizes range to range relationships RATIOMETRICALLY (important term) against its internal 10 VDC reference, 10 Kilohm input and electrically established zero offset cal factors.

This is only a confidence check, and not at all a true calibration. There is a principle in metrology called the principal of uncertainty growth. That is, from the moment you adjust/verify a measurand, the uncertainty of what it's true value grows at some predictable rate. The 3458A above will drift away from it's actual values, and the AUTOCAL function will ratiometrically, re-establish all ranges, etc. against those drifted values. So by a years time (statistically, anyway), that 3458A will have drifted out toward it's tolerance limits. I have high respect for the 3458A, so don't anyone interpret this as negative toward it.

The only way to re-establish the 3458A against known accuracies, is by verifying it's relationship to NIST (or other) traceable values. The purpose of traceability is to assure everyone is on the same page (so to speak).

I can pretty well assure that if you design an instrument that measures NIST traceable parameters, and engineeers design it only to "SELF-CALIBRATE" (an oxymoron), it will, over some predictable time, drift away from true nominal.

So No, you can not self-calibrate any instrument. About the only exceptions (crazy, but for the sake of illustration) would be physical constants. If you built a Cesium Beam or a GPS receiver into a unit, it would not need external frequency cal. If you built a Triple Point of Water (not really feasible) into a unit, it would not need zero degree Celsius cal. But these things are not feasible.

Let me throw in a qualifier on my above posting. If your engineers design a "GOLDEN UNIT" to calibrate your instrument, this may potentially simplify the process greatly. The GOLDEN UNIT would require NIST traceability. If your GOLDEN UNIT adequately covers function/ranges of your instrument, it may do what they require. The question is assuring the GOLDEN UNIT has adequate coverage. It does not replace NIST traceable calibration, it simplifies it.

I hope this helps.
 
J

joecalibratio

#3
Thank you so much for the response. I battle with our engineers because they resist the point of "adequately covers function/ranges of your instrument" by argueing that it is all digital and a failure would not result in an oot condition but a total failure (no signal/data versus and improper signal).

Joel
 

Jerry Eldred

Forum Moderator
Super Moderator
#4
I've had numerous instruments over the years where the OEM said it didn't need calibration (for some reason, none of the models currently come to mind). As a Metrologist for nearly thirty years, you can accomplish a lot ratiometrically. However, in my humble opinion, no quantitative instrument which measures a traceable type parameter can function accurately for an indefinite period without benefit of external tracability.

The only exception (anomaly) I can think of is the Fluke 77. One company years ago had a very large inventory of Fluke 77 handheld multimeters (can't remember their name; but I believe it was a major defense contractor type company). With thousands of the meters in their inventory, over something like ten years of history, they had zerro out-of-tolerances. So they removed calibration intervals based on that. However, I have had to adjust even those, I have had dFluke 77's with deteriorated range switches (that cause intermittend ohms), and other problems. So although one of the most robust handheld multimeters ever made, it is not completely above the need for external calibration.

Bottom line... no instrument is completely exempt from calibration (if you want what it measures to be quantitatively accurate as relates to the rest of the world.
 

BradM

Staff member
Admin
#5
Awesome posts, Jerry! Thank you.

Ok, you have device D.U.T. that works on it's own. You have this "standard" device that becomes integral with the D.U.T. Is the standard just using power from the D.U.T.? What type of algorithm is the standard utilizing to assure the D.U.T. is working properly? Is there some measurement verification of some kind?

If the customers purchase the D.U.T., will they have to buy the standard also? Can you re-certify the standard?

Are these devices constant voltage (120 vac), or battery operated? Do they have low voltage shutoff?

What kind of verification will be performed on the standard to assure it's continued success?

Jerry is right on. In my shortened life I have seen multiple setups, due to necessity. Somewhere in that system you will need a N.I.S.T. verification to assure that nothing has gone haywire.
:topic:
I don't know about you folks, but I wished everyone did things like Fluke. First, their equipment is so good. Too, most people believe their stated tolerances are quite conservative.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#6
Good question and some good answers.....

As for what Fluke does, their NVLAP accredited lab has a Josephson standard that provides as direct as possible to SI.

If the manufacturer in question here has a similar arrangement, then the traceability change can be easily established.....otherwise the calibration standards need to be sent out.....

One other thing to consider.....most manufacturers of test and measurement equipment are not calibrated.....this manufacturer should consider accreditation to ANS/ISO/IEC 17025 for its calibration operation.....

Hershal
 
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