Re: Replacement meter has fsd current about three times old damaged meter.

On Jul 29, 4:10 am, Franc Zabkar <fzab...@xxxxxxxxxxxxxxxxx> wrote:
On Mon, 28 Jul 2008 20:52:07 -0400, Dave M <masondg4...@xxxxxxxxxxxxx>
put finger to keyboard and composed:

A transimpedance amplifier is what you need, as Sam suggested.  Here's a circuit
to start with.   You might have to fiddle with exact resistor values, depending
on the Op-amp you use, which isn't critical, except for input offset voltage.
Select a dual Opamp with low offset voltage, such as the Texas Instruments
OPA2227.
Since it only sees DC currents and voltages, there are no issues with frequency
response.  The circuit runs off a 9V battery ...

I don't mean to nitpick your clever circuit, but you've drawn it as
running off *two* 9V batteries. Maybe you should have designated the
battery terminals at V+ and V- rather than +/-9V.





          +9V
           |
         +-+-+
         |   |
         |   |      +-------------+
     10K |   |      |             |
     1%  |   |      |    +9V      |
         +-+-+      |     |       |
           |        |  |\ |       |
           |        |  | \|       |
           |        +--+- \       |
           |           |   \U1B   |
           |           |    ------+
           |           |   /      |
           +-----------++ /       |
           |           | /|       |
           |           |/ |       |
         +-+-+            |      +++
         |   |           -9V      +
         |   |
     10K |   |
     1%  |   |
         +-+-+
           |
          -9V

Cheers!!!
Dave M

Never take a laxative and a sleeping pill at the same time!!

Wise words.

- Franc Zabkar
--
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Great replies: thank for the thoughts and information.
Also for the unit specification; had no indication is was 25 mhz. up.
But the small size/length of the transmission line unit inside it
might have been some indication.
Seems to boild down to a) Look at and modify/jigger the values of the
resistors in the DC part of the switching circuit to increase meter
deflection 'as is'.
.

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