wacky DVM [RE-wrenches]

[jay peltz]

Hi John,

I know that there have been problems with that meter for a while.  The
second version works pretty well, but then problems like this appear.  I'd
like to know if this fixes the problem.  The person whom designed it, passed
away so I don't know if there will be any revisions or not.

jay

Peltz Power

John Berdner wrote:

> Jack,
>
> I am not familiar with the IOTA but I think it is a switch mode charger.
> The high frequency switching noise could be leaking into the meter.
> The noise gets in through the meter's power leads or the voltage sense
> leads (if any).
>
> High frequency noise was a problem with some of the old APT 3 meters in
> 48 Vdc systems. It ended up being a power supply oscillation at > 1 Mhz
> so it was really hard to find.
>
> You could take a look for noise on the dc line with a scope or try
> filtering leads to the meter. If you make one up with clip leads on all
> 4 wires then you can try it to see if it this solves the problem
>
> Something like this: (ASCII Draw)
>
>   B+ -- 10k to 100k resistor --|-- Meter sense +
>                                |
>                       1uF to 10uF capacitor
>                                |
>   B- -- 10k to 100k resistor --|-- Meter sense -
>
> If the meter has separate dc supply and sense leads you might have to
> filter both.
> The input impedance of the meter sense leads should be high enough that
> the resistors will not effect the accuracy of the measurement.
> I don't know how much power the meter draws so you might have to
> decrease the values of the resistor and increase the size of the
> capacitor on the meter power leads.
>
> Hope this helps
>
> If you have any questions or I can be of any further assistance please
> do not hesitate to contact me.
>
> Best regards,
>
> John Berdner
>
> SMA-America, Inc.
> 20830 Red Dog Road
> Grass Valley, CA  95945
> Tel: 530.273.4895
> Fax: 530.274.7271
>
> ----- Original Message -----
> From: "Jack West, Talkeetna AE" Sent: Monday, May 28, 2001 12:51 AM
> Subject: wacky DVM [RE-wrenches]
>
> DVM works well and reads accurately until Iota comes on
> > line, then reads about 3 volts high.  Problem goes away as soon as
> > charger is unplugged.
>
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