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 Post subject: Voltage Meter Calibration Requirement
PostPosted: Wed May 14, 2014 12:41 pm 

Joined: Tue Oct 29, 2013 7:29 am
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I can't seem to locate anything on this so I place the question to you:
Is there an OSHA or NFPA-70E requirement that my Fluke Series 83-III MultiMeter must be tested/calibrated beyond the requirement its operation be tested satisfactorily before and after checking for voltage?
I seem to recall that the equipment should be maintained according to the manufacturers recommendation which I believe is 1 year in Fluke's case. Thanks.

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PostPosted: Thu May 15, 2014 6:35 am 
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"Proper maintenance" of any equipment is to put it lightly, an art.

OSHA requires that you test before testing for absence of voltage, copying a requirement from a 20 year old edition of 70E.

The current 70E requirement is to test before and after testing for absence of voltage. This is a safety requirement to verify that the meter is working correctly throughout the test.

However, NEITHER document talks to how to actually do the test itself, accuracy requirements, etc. In fact 70E incorrectly refers to IEC/UL 61010 as a reference document for the test. That standard is a meter design standard and speaks to the "Category" rating system for meters which is designed to prevent a meter from exploding due to a transient. It never once talks about actually taking measurements. It doesn't give any specifications as to the actual tool to use or anything else.

There are ISO standards for actually doing a test for absence of voltage. They give specific accuracy requirements for meters and trust me, they are far less accurate than the manufacturer's requirements. During the last 70E revision cycle for the 2015 edition I submitted the ISO documents to replace the IEC/UL reference. This was rejected for procedural reasons.

Fluke documents their meter accuracy. The accuracy is to put it mildly, vastly greater than what is required for safety purposes (testing for absence of voltage). Knowing how much the meter may drift or otherwise lose accuracy, they then go on to specify a calibration frequency of one year. But here's the rub with that. Say the meter is stated to be accurate to 1%, which Fluke is far more accurate than that. The IEC/UL standards for testing for absence of voltage have an accuracy requirement of closer to +/-20% or more. So if the meter may drift by 1% per year (thus the calibration requirement), it would take 20 YEARS to drift far enough out to fail a +/-20% requirement, assuming that it is linear in drifitng, which is usually not true.

Thus, meter accuracy is actually almost immaterial for safety purposes. Far more important is whether or not the meter is properly functioning at all during the test. In other words whether or not it undergoes a catastrophic failure during testing. This kind of issue would most likely never show up by sending the meter out for calibration once a year because it's not just a meter drift issue. Most likely one would either correct the problem (replace the fuse, replace the batteries, or replace the whole meter) rather than wasting money on calibration if a meter is no longer functioning to that degree.

So if you are trying to measure accurately with a meter to say meet ISA specifications for testing/calibrating equipment, then you need a meter that is far more accurate than the equipment that is being calibrated. In this particular instance it is probably necessary to have NIST traceable levels of accuracy, calibrating a meter once a year as recommended by the manufacturer or more if the drift rate is more than that, and so forth. But for a safety test none of this is really necessary at all. This is most likely the reason that 70E, OSHA, and even the proper ISO documents are totally silent on the calibration subject.

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