[Milsurplus] RF Ammeter Question

[J. Forster]

No, it most certainly is not for a good TC meter. Is it repeatably 2:1?
(Might it be a contact resistance issue?)

Does the resistor look tacked on, as an afterthought, or is it clearly
original to the meter?

Can you disconnect the resistor and measure the resistance across the
meter terminals directly? It should not be more than a few Ohms.

Is it possible the meter has been internally modified?

Best,

-John

===========



> Thanks John.
>
> I'm using just an old C battery.  The meter reads OK regardless of the
> polarity of the battery,  but the reading is different by almost 2:1
> depending upon the polarity.  Is that normal?
>
> Mark K3MSB
>
> On Sat, Dec 1, 2012 at 2:48 PM, J. Forster <jfor at quikus.com> wrote:
>
>> You can easily tell if the thing has an internal shunt by running some
>> DC
>> current through it and a series limiting resistor, first one way, then
>> the
>> other.
>>
>> If the meter indicates positive, irrespective of the current direction,
>> it
>> has a TC.
>>
>> If the meter reads upscale one way, and downscale the other, it has no
>> TC.
>>
>> You can also apply 60 Hz AC through a resistor. If it indicated upscale,
>> it has a TC.
>>
>> The meter should have response from 50 Hz to 10s of MHz roughly.
>>
>> It is odd to see a current meter with a resistor paralleling the
>> terminals.
>>
>> -John
>>
>> ============
>>
>>
>>
>>
>> > I rescued what looks to be a perfectly good Simpson RF Ammeter from
>> the
>> > clubs trash can a while back.  It’s a 3 inch square panel meter, 0 to
>> > 2.5A,
>> > logarithmic scale,  with a 0.05 ohm 25W resistor solder to the
>> terminals.
>> >
>> >
>> >
>> > I’m not sure how to tell if this has an internal thermocouple.  I did
>> some
>> > web searching and it seems Simpson did make these types with the
>> internal
>> > thermocouple, but I haven’t found anything that tells how I can
>> verify.
>> >
>> >
>> >
>> > I’ve never used an RF Ammeter before, so I assume I use it just as a
>> good
>> > old DC Ammeter?   Is there a frequency limitation?
>> >
>> >
>> >
>> > Thanks
>> >
>> >
>> >
>> > Mark K3MSB
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>>
>>
>>
>