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April ESR Tester, 100uA use 50uA meter

Jul 9th, 01:43

KB0MNM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi Zack & others at ARRL-
I was getting ready to try building the Capacitor ESR tester as detailed in April's QST magazine. Unfortunately, the local parts store had no 100uA meter movements. They did have one for 50uA.
So a repeat of how to determine the correct shunt resistor might save me a bit of effort.
I also noticed that QST later mentioned one error with respect to the pins 8 & 4 of the power to the TL082 op-amp ( one section only, the second one ). What they did not mention was that if you look at the magazine article the floating supply voltages are + and - 4.5 volts derived from the 9V battery. The other drawing ( downloaded with the PCB layout ) shows + and -9 V, very difficult to derive without a chip such as the ICL9660. I was really hoping for a line-powered rather than battery powered supply for this project.
An "Arduinio" hybrid would also be a great idea, but then if all wishes were granted some of us would fly without machines...
Thanks in advance- 73- KB0MNM Jon jkliv@comcast.net
Jul 9th, 13:33

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

I'd suggest putting a 180k ohm resistor in series with a 9V battery and measuring the voltage drops across the resistor and the meter, to determine the resistance of the meter. Alternately, you can often look up the resistance of a new meter. If the shunt has the same resistance, the full scale current will double.

http://www.circuitstoday.com/frequency-to-voltage-converter
This page shows how to build a +/-5V supply

Zack Lau W1VT
ARRL Senior Lab Engineer

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