[Test-Equipment] HP 403B pegging meters

[J Forster]

There are two issues:

The first is if the current pulse has enough energy to burn out the coil. If it
does...  that's curtains.

The second is the mechanical issue. Some meter movements are heavily damped. If they
are, a short current pulse will not ram the thing against the stops and cause
mechanical damage. Think Ballistic Galvanometer.

Best,
-John



WA5CAB at cs.com wrote:

> I was going to comment earlier but got sidetracked.  Although the movement
> (coil and springs) may survive a 10X overload, whether the needle and peg does
> will depend somewhat upon how it got from o to 10X.  Repeatedly hitting the
> meter with a step function (rectangular pulse with zero rise-time) that bangs the
> needle against the peg will eventually bend the needle.
>
> I'm not familiar with this instrument  (and forget what the original post
> said it even did)  But as in this case, it doesn't appear that the absolute
> reading accuracy of the meter is critical (one respondant reported using a 0-500 uA
> movement as a substitute), one could series a current limiter set to say 125
> uA.  I don't know that anyone builds and sells a range of 2-terminal devices
> but they might.  Or you could build or buy a 3-terminal one.
>
> In a message dated 3/13/2008 10:11:29 AM Central Standard Time, k4pf at juno.com
> writes:
> > Hi,
> >
> > I'm glad to hear that HP meters can stand such an overload,
> > but I can report that not all good quality panel meters
> > can survive.
> >
> > I once connected my Triplett model 666HH VOM (1K Ohm/Volt, about 1950
> > vintage) across 125VAC when the meter was set to the 50VAC scale.
> > The meter coil survived, but I had to do surgery on the meter
> > to straighten out the bent indicator.
> >
> > 73,
> > Ed Knobloch
> >
> >
> > -- w8au at sssnet.com wrote:
> > >As pointed out in earlier postings, this is not a problem.  The meters will
> > withstand 1000% overload without damage (even though to our eyes it looks
> > abnormal).   In that you've shown that the surge is 400%, this is well
> > within
> > the normal safety specs for the meters.
> >
>
> Robert Downs - Houston
> <http://www.wa5cab.com> (Web Store)
> MVPA 9480
> <wa5cab at cs.com> (Primary email)
> <wa5cab at comcast.net> (Backup email)
>
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