Calibrating El-Cheapo Test Equipment

J

Jim Mitchell

#11
Randy Stewart said:
Having gone through this also, here's my 2 cents.

Why was the equipment there in the first place?
If it is being used what is it measuring?
Have there been any rejects that can be traced back to the equipment?
I'm sure you get the picture. If the equipment isn't being used - scrap it or have the person take it home. If it is for other projects and has nothing to do with QA then mark it. If it is being used for a QA measurement and no reject can be traced back to it, then what purpose does the measurment have?
Or is the equipement adequate enough.
I agree, and to take it a step further, if those tools are not being use for acceptance measurements, why not label them "Reference use only" and not worry about them?
 
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ScottBP

Involved In Discussions
#12
A lot of times (and we do it where I work), cheap meters are used for troubleshooting purposes only, e.g. checking fuses, batteries, continuity from point A to point B, etc., as opposed to taking "official" readings that are entered on a data sheet, or used to perform a calibration. For ours, we put "calibration not required" stickers on them and in the comments section write in "for troubleshooting only".

And quite the opposite happens too... Despite having a number of good meters (e.g. Fluke 87s), some people label them cal. not required, despite the valid reasons why they should have them calibrated, simply because they don't want to pay to have every meter calibrated by an outside vendor. Instead, they compare them in-house to a calibrated meter on an as-needed basis.

I have access to GIDEP, and usually reference a USAF T.O. or Navy NAVAIR procedure for a meter that has very similar functions, or we have our own in-house procedure that has loose tolerances for the stuff we just can't find any info on, no matter how hard we look.
 

Jerry Eldred

Forum Moderator
Super Moderator
#13
There are many alternatives to "how", but the bottom line is assuring (by what ever means works for your company) that adequately calibrated instruments are used where process or product quality can by impacted.

I won't get legalistic on the following point, but I feel duty bound to at least voice a view (and see what some others think).

I have long believed that any measuring instrument should be calibrated. This is above and beyond the minimal "pass an audit" philosophy. My reasons are that there are other implications.

For example: A multimeter that is used to check AC line voltage (in a GO-NO-GO context). Perhaps you don't care whether the voltage is 5% or even 10% off in this situation. However, what are the implications to the incorrect reading? They may not be product defects, but more importantly, they may be a decision that the circuit is de-energized so someone can perform maintenance (or other reason).

For troubleshooting (and much of my background is in electronics repair): if I am using an uncalibrated meter to check transistors or resistors in a curcuit. The uncalibrated meter is of unknown accuracy. What are the implications to my troubleshooting? Do I end up misdiagnosing because a range (or ranges) on my DMM are either way out of tolerance or inoperative?

I'll also refer back to my "lightbulb with pigtails" illustration. If I didn't care what the reading was on the meter, I could have use a lightbulb with pigtails. If I am using a meter and reading the displayed value, I am by definition interested in a quantitative measurand.

I have been involved in many management meetings over the years about this issue. One factory at an company I am related to had a population of a few hundred Fluke 77's and 87's (and those families). They wanted to take them all off from the calibration program because they felt the meters didn't need to be calibrated due to their use. The real reason was cost savings.

Granted, the above meters are good quality and tend to remain in-tolerance for a long time. But no meter stays in-tolerance forever. My recommendation was to lengthen the calibration intervals. They had a 12 month interval. My input was the 2 or even 3 year interval would be better than never calibrating. As high a regard as I have for the above example meters, I have over the years had to align members of both model families.

I don't intend anything derogatory toward anyone's method of determining calibration intervals or whether or not to calibrate troubleshooting type multimeters; only to go on record about this philosophy. So please don't anyone take any offense.

I'll be interested in hearing some of the other views on this (or if anyone agrees).
 
R

Randy Stewart

#14
Jerry,

I agree with the troubleshooting meters you mention. I have worked on many transformers and rectifiers during my years on submarines.
I think what Scott was mentioning was a "non-reading" needle deflection type check. Similar to wetting your fingers and quickly touching 2 leads :mg: .
Or the 9 volt battery on the tongue test.
What I refer to most is the person with calipers where the depth portion becomes bent and all he is verifying is that the hole is deeper than 4".
I have no problem with exchanging personnel safety with a quality measurement. All you need to do is rely on a broken meter to tell you that the capacitors in a, 1980s technology built, 14kw recitifier are discharged and then use a shorting rod (for backup) and see a beautiful blue fire ball bounce off your face shield to agree with you!!!:yes:
 
C

cbehrens

#15
I have to wonder why some one would send you a meter that cost three times the original price to calibrate. If they were accurate enough to suit the task when I purchased them I always reguarded them as disposable at calibration time. Buying another new one and doing some product revarification to make sure nothing was askew. I also found that the cheaper equipment didn't do much worse that the expensive stuff when someone dropped it from five feet or managed to roll it over in a two-thousand ton press.
 
R

Randy Stewart

#16
It is amazing how things "get rolled over" in a press. I've seen people leave the can of prussian blue in the press. We're talking BIG MESS. Not to mention grinding wheels (does wonders on a class 1 surface!), pens, union buttons, etc.
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#17
Think about it folks......Phil Stein was on track.........

If the measurement matters.....you need to calibrate.....

If the measurement does not matter, why do it?

That applies whether certifying equipment, or as Jerry has so correctly pointed out, even for troubleshooting.....

Hershal
 
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