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Technical Discussions
Paul Wray
Paul Wray
07:39 Feb-05-2003
MPT bench current meters

Can anyone explain the industry situation as regards the problem below? (NDT is not my field, but I am editing/writing some vocational-level educational materials on MPT.)

THE PROBLEM:
Lets say you want do follow an MPT method - eg for testing some component of standard dimensions - developed elsewhere, which specifies a magnetising current. You want to generate the same current with your unit.
Now the MPT test bench at out college (a "lectro-flux BWD 1565") has a simple moving coil meter, and an AC-DC selector. The machine is old, and I dont have access to the manuals.
There is no indication of whether the meter is indicating RMS or peak, and no indication of whether "DC" means half- or full-wave rectified. In addition, even if I knew the meter was indicating RMS for an AC current, can I trust the manufacturer to have included circuit to account for the change in form factor, so that the current reading for a "DC" current is also true RMS? Or is the reading on DC really meaningless - for comparison purposes only?
My questions are:
1)Can one trust the indicated values from moving coil meters on MPT benches to be true RMS ?
2) Is is a typical situation to not know the "true" value of the current, except to be able to compare a current with others generated on the same machine ?
3) Is it rare situation to want to carry out a procedure developed on a different machine? Or must it be re-validated on every machine?
4) Does anyone have any horror stories stemming from blindly believing a quoted current in a procedure, or blindly believing the current reading of an MPT bench ?





 
 Reply 
 
Neil Burleigh
Sales
Krautkramer Australia Pty Ltd, Australia, Joined Dec 2002, 159

Neil Burleigh

Sales
Krautkramer Australia Pty Ltd,
Australia,
Joined Dec 2002
159
02:58 Feb-05-2003
Re: MPT bench current meters
: Can anyone explain the industry situation as regards the problem below? (NDT is not my field, but I am editing/writing some vocational-level educational materials on MPT.)
.
: THE PROBLEM:
: Lets say you want do follow an MPT method - eg for testing some component of standard dimensions - developed elsewhere, which specifies a magnetising current. You want to generate the same current with your unit.
: Now the MPT test bench at out college (a "lectro-flux BWD 1565") has a simple moving coil meter, and an AC-DC selector. The machine is old, and I dont have access to the manuals.
: There is no indication of whether the meter is indicating RMS or peak, and no indication of whether "DC" means half- or full-wave rectified. In addition, even if I knew the meter was indicating RMS for an AC current, can I trust the manufacturer to have included circuit to account for the change in form factor, so that the current reading for a "DC" current is also true RMS? Or is the reading on DC really meaningless - for comparison purposes only?
: My questions are:
: 1)Can one trust the indicated values from moving coil meters on MPT benches to be true RMS ?
: 2) Is is a typical situation to not know the "true" value of the current, except to be able to compare a current with others generated on the same machine ?
: 3) Is it rare situation to want to carry out a procedure developed on a different machine? Or must it be re-validated on every machine?
: 4) Does anyone have any horror stories stemming from blindly believing a quoted current in a procedure, or blindly believing the current reading of an MPT bench ?
.
.Paul,
Give Dave Mullet a call at Lectromax Australia 03 94311041 admin@lectromax.com.au. I think they made the mag bench you are talking about.
Also I always recommend that mag flux indicators be used on the test piece because you cannot guarantee the output of the test bench is transferred completely into the test piece.

Regards
Neil Burleigh


 
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