Can some one please tell me why Manufacturer's continue to put 2-Wire 0 Ohms test points in their test procedures. Then put a statement that the meter must be zero-ed to remove lead resistance with a short before you can make an accurate measurement.
You connect the short, zero the Meter, then write down zero on the test report. Has no one in the industry came to the conclusion that 0-0=0.
I am not saying this test is completly point less, if anything you are checking the Meter ability to hold a stable Zero Ref. So the test should read something like: Connect a short, press Zero, wait 2 minutes and verify the Zero Ref has not changed more that x Ohms.
Am I missing something here?
Mike
Mike,
Not sure what meter you are talking about, but I have noticed similar things. But, it does make sense when you think about it.
For example, if I am doing a 34420A, I am using a shorting plug for the 0 ohms verification and for the adjustment (if it is needed). And, it seems to me, the internal whizzits need that 0 ohm reference to base the other values off of. I have seen the 0 drift some, or else it was 'adjusted' by someone previously that did not recognize the meaning of allowing the plug to mate thermally with the meter (I love calibration, we get to make WAY too many uhm, 'references', that are perfectly acceptable).
Now, I might be totally off kilter here, I'm not usually a DC/Low guy. but unfortunately, sometimes I end up dabbling in that arena.......
Oh, and Joe Snuffy needs to zero out his test leads when he is measuring his whatzit because 9/10 times, he is using 30-50 foot leads......
J.. I agree with you on an absolute 2-wire zero test. With a calibrated shorting plug. Those procedures do not have a little note in them saying you must zero the meter before you can make a measurement.
Those procedures say connect a shorting plug (and specify shorting Plug) then measure the 2 wire zero without pressing the set reference.
But if they only way you can get the UUT to pass 2-Wire Ohms zero is to press the Ref/Zero button. And there are not Adjustment Points for 2 Wire Ohms zero.. Then the test points should be dropped.
And Yes.. Agilent have very good Metrology Practices, it is kind of like they know what they are doing.
I am surprised to hear that. Agilent makes their share of Metrology mistakes.
Ah, I see. You are talking about the moron mfrs that have you zero it then check the zero. Yeah, think that is mostly a check to see if the meter can even zero itself...... lemme guess, it's a little $5 meter from Harbor Freight? (which I have one at home, lil thing is great, but yeah, have to zero ohms....)
J, No It is not a $5 dollar meter.
RF-Cal.. Yes they do. And I have caught every manufacturer in a what the F#@k do you think you are doing. But I am an Agilent Partner.. So I have to point out they are much better than the rest of the manufacturer's. Product for product they are less mistakes.
Mike
As I think about this.. My problem is I have to write the steps in the automated procedure exactly how the written procedure calls them.. Well as close as possible..
I make is an absolute measurement and fail units, the customer complains about the software.. If I set the Ref and Read 0.0000000, I think hmmm I could shave 30 seconds for each test point off the total calibration procedure by skipping the test that are not really testing anything.
Mike..
Quote from: CalLabSolutions on 07-28-2011 -- 15:13:21
But I am an Agilent Partner.. So I have to point out they are much better than the rest of the manufacturer's. Product for product they are less mistakes.
Mike
Thanks for pointing out that you are an Agilent partner, Mike. While I agree that their metrology practices have generally been sound, tell me how they can specify a Fluke 5520A calibrator as being an adequate reference to calibrate a 34410A/34411A DMM with TARs, in some cases, less than 1:1? Better yet, I'd like to hear Agilent's rationale for it!
There are, however, many manufacturers, other than Agilent, that I believe also have credible metrology practices, but anyone can make a mistake.. even you Mike :wink:
Quote from: measure on 09-04-2011 -- 10:56:05
Quote from: CalLabSolutions on 07-28-2011 -- 15:13:21
But I am an Agilent Partner.. So I have to point out they are much better than the rest of the manufacturer's. Product for product they are less mistakes.
Mike
Where are you getting
Thanks for pointing out that you are an Agilent partner, Mike. While I agree that their metrology practices have generally been sound, tell me how they can specify a Fluke 5520A calibrator as being an adequate reference to calibrate a 34410A/34411A DMM with TARs, in some cases, less than 1:1? Better yet, I'd like to hear Agilent's rationale for it!
There are, however, many manufacturers, other than Agilent, that I believe also have credible metrology practices, but anyone can make a mistake.. even you Mike :wink:
I am not going to say I never make mistakes. I will say I have learned from everyone of them.
However, no one is saying or implying we should be using a Fluke 5520 to calibrate Agilent 34410A/11A. I don't recall ever seeing an Agilent Procedure calling for the Fluke 5520A. So I am not sure where you are trying to go with this?
Yes, yes I do were my Agilent Channel Partnership like a badge of honor. I don't have deep pockets, a million dollar a year marketing budget or a world-wide sales force. I compete on service and quality, so becoming an Agilent Solution Partner because Agilent hears good things about my company. :-)
Quote from: CalLabSolutions on 09-06-2011 -- 14:33:02
I don't recall ever seeing an Agilent Procedure calling for the Fluke 5520A.
Look in the Service Guide for the 34410A/34411A located on the Agilent website...
Quote from: CalLabSolutions on 09-06-2011 -- 14:33:02
So I am not sure where you are trying to go with this?
Only to reinforce the fact that, no matter how good ANY source might be, NONE are infallible. I'd still like to hear Agilent's rationale for this...
34410A/11A Recomended Standards
Agilent 34172B
Fluke 5720A
Agilent 33220A
IET SCA–1μF
Page 60 of service manual Part Number "34410-90010"
34410-90010, 34410/11 service manual jan 2006 2d edition
34410-90010, 34410/11 service manual apr 2006 3d edition
34410-90010, 34410/11 service manual feb 2007 4th edition (this is the service manual on line at present) call for 5720A.
Please link the manual you are referring to.
Speaking of slightly off topic... Ever heard of the Ohm Labs zero ohm standard. It is certified to less than 50 nano Ohms in any configuration. At that point, lead balancing is essentially the sum total of resistance.
Not familiar with it (or what for). I hope you & yours are safe from the fires. I don't think that I've ever seen it this bad in my time in TX (since 85).
Just taking a WAG to answer the original question, I'd say the reason that 2-wire tests are still valid is that more than half the users have their meters configured and use them that way.
Quote from: michthai on 09-07-2011 -- 17:42:15
Just taking a WAG to answer the original question, I'd say the reason that 2-wire tests are still valid is that more than half the users have their meters configured and use them that way.
I agree we need to calibrate 2-wire ohms, just not 2-wire ohms 0 Ohms when the specifications state you have to zero out the lead resistance.
100 Ohms test where you short the leads press null. Then apply 100 Ohms... That makes sense. But doing it with a 4-Wire short does not make any sense unless meter has a separate 2-wire zero ohms spec that does not require a lead zero requirement in the spec.
Mike
Quote from: Bryan on 09-07-2011 -- 13:35:32
34410-90010, 34410/11 service manual jan 2006 2d edition
34410-90010, 34410/11 service manual apr 2006 3d edition
34410-90010, 34410/11 service manual feb 2007 4th edition (this is the service manual on line at present) call for 5720A.
Please link the manual you are referring to.
Thanks Bryan. The current manual does, in fact, reflect the use of the 5720A.
As to the original question, I believe the intent of a 2 Wire Ohms test is to verify the integrity (e.g., thermal emf and contact resistance) of the input path. When you install a short and subsequently set an offset (null) on the meter (typically on the lowest range), you are 'mathematically' removing the effects of lead and contact resistance, with respect to the installed short, at a specific point in time. If, however, the input path has excessive thermal emfs or contact resistance (physical effects), for example, the display, though initially nulled out, will continue to drift and/or show excessive, out of tolerance readings. If out of tolerance conditions are detected when subsequently measuring 2 Wire resistance on higher ranges, it would also expose the possibility of range relay problems existing, perhaps where a 4 Wire Ohms test might not.
Quote from: Bryan on 09-07-2011 -- 17:07:03
Not familiar with it (or what for). I hope you & yours are safe from the fires. I don't think that I've ever seen it this bad in my time in TX (since 85).
BRYAN - Thanks for the thoughts. It is really bad. I live NW of Austin, and have had two wildfires very close to where we live. One a few weeks ago destroyed 15 homes, and as we drove home, various streets were closed off, all along our street, everyone was using their lawn sprinklers as a precaution, we saw ashes floating down as we drove home, and there were forest fire planes and helicopters dumping retardant and water within a half mile of us. Then in the most recent ones, there was another fire maybe a quarter mile further away. But no one has had it as bad as the folks in Bastrop. I heard that over 800 homes are destroyed there, and over 1000 homes destroyed in total (all the fires). They have it pretty much controlled now, but it is not done.