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October 14 - October 18, 2019

How do you calibrate a DFT gauge in the magnetic field of a live power plant to measure coatings on steel substrates?


Selected Answers

From Julian Hay of JhayCon Inspection and Consulting on October 18, 2019:
You may be able to calibrate normally if you move around the area until you find a place where the field is less. Though much good may that do you if you are then going out into the area and attempt to take measurements where there is a still strong field around…..you will still be unable to take readings except sporadically where the field is weak. Your gauge will simply sit there and do nothing and you will become very annoyed and start thinking evil thoughts about the gauge manufacturer. I used to do this a lot, and not just in power plants.  These days there is so much EMF interference from Wi-Fi or cell towers and boosters that it is not uncommon to encounter exactly the same problem in shipyards or buildings or cities. OK, so the solution(s) are fairly simple: get one of the more modern very recent gauges that have better shielding conformance and use a fixed probe rather than one with a cable. (That cable picks up the field also.). This combination works most of the time, for me at any rate. Actually, the newer cables and gauges are pretty good most of the time. I have one (bought out of frustration at my 8 older units, and I find only a really strong field (very rare) can give it problems,  but there is a solution for that, too… read on.   For a field-expedient solution, if you only have a cabled probe, wrap it up into a tight bundle so you are not exposing a great length of cable. This will diminish the pick- up of the field and may be sufficient to solve the problem.   If you must use the cable fully extended,  wrap it in tinfoil, and don’t laugh (or feel embarrassed), even though you look like an idiot. This does actually help if you are in a pinch. Better yet,  get some shielding mesh from The Source or some such place and use that around the cable and gauge, if necessary. (And yes, wrapping it in tinfoil and coiling the cable may help.) If it is still not working, then there is probably a new gauge in your future, as you can’t use that digital magnetic artifact in your hand. You need to pull out a banana gauge or use eddy current or ultrasonic or a Tooke gauge. Any of those will work normally, though frankly, the last two can be pretty annoying but at least you can get the job done. Good luck dealing with magnetic and EMF fields in the increasingly, electronically polluted world.

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Tagged categories: Dry Film Thickness (DFT); Quality Control; Steel; Thickness gauge


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