pcba
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I can't get my circuit to work! What I want to do:
Measure the resistance (in fact voltage) of copper foils with the 4 probe method and amplify the output with i.e. an AD623 (tried INA126 too) instrumental amplifier. I attached a circuit of about what I am using.
Just to get some figures I checked with a multimeter (which is probably not accurate in that low range) on different foils:
18µ/H oz 800µV / 0.07mA
35µ/1 oz 400µV / 0.04mA
175µ/5 oz 100µV / 0.01mA
The mV output is about what I expect, and what I like to bring in a range to use with a µP.
Supply to the foil (outer pins, no load) is 9V , current is 1.1A with load
With the pot on pin 5 I can regulate the output (pin 6) to near zero (±10mV) - but when measuring the different foils I get pretty much the same output. Also, when I change the gain (pin 1 + 8) I get no change in output.
I tried also pin 5 direct to ground and grounding either pin 2 or 3 and one of the measure pins to gnd - whatever I do, I don't get a meaningful output.
It seems I do something fundamentally wrong and hope somebody can help.
(an error in the drawing: I use 3R9 and not 2R)
BTW, the oscilloscope I have between pin 6 and GND
Measure the resistance (in fact voltage) of copper foils with the 4 probe method and amplify the output with i.e. an AD623 (tried INA126 too) instrumental amplifier. I attached a circuit of about what I am using.
Just to get some figures I checked with a multimeter (which is probably not accurate in that low range) on different foils:
18µ/H oz 800µV / 0.07mA
35µ/1 oz 400µV / 0.04mA
175µ/5 oz 100µV / 0.01mA
The mV output is about what I expect, and what I like to bring in a range to use with a µP.
Supply to the foil (outer pins, no load) is 9V , current is 1.1A with load
With the pot on pin 5 I can regulate the output (pin 6) to near zero (±10mV) - but when measuring the different foils I get pretty much the same output. Also, when I change the gain (pin 1 + 8) I get no change in output.
I tried also pin 5 direct to ground and grounding either pin 2 or 3 and one of the measure pins to gnd - whatever I do, I don't get a meaningful output.
It seems I do something fundamentally wrong and hope somebody can help.
(an error in the drawing: I use 3R9 and not 2R)
BTW, the oscilloscope I have between pin 6 and GND
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