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ICL 7107 Ammeter

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Having my DVM all soldered up ,calibrated and running solid..actually the performance is much better now than when it was on the breadboard..I moved into an Amp meter using another chip. I'm hoping for 19.99 amp metering..having 100 and ten's of milliamps I think would be quite handy ...realistically i cant see this unit measuring more than 10 amp from my intended power supply..but im a head room fanatic ..and try to not run anything more than 60% of its intended purpose or rating.
I got it to run but the calibration is whacked..It wont zero out at 100 mv, 300 to 1v is fine.It floats but no different than my DMV when it was on the breadboard.
I used the Intersil data in tandem with online schematic..essentially i set this meter up how intersil suggest for the volt meter minus the 1meg resistor..then turned to online schematics for the rest..

The problem im sure is the shunt resistor a cement 5watt 1ohm..
I use a known variable low and high amp load..tested with two digital multimeter's and an analog ampere meter..38-40 milliamp at idle,fully loaded at 1.98-2.00 amp respectively..
On the 1volt reference scale i can sort it out to read the correct 38 milliamp idle current..but at full load it will read only 1.29 amp
At 100 millivolt reference ..set to read the correct 38 milliamp idle current it will read 1.75 amp at full load..but the meter is wild..rolling 20-30 milliamp +/-..

at a loss ..I set up a voltage divider with a 2.2 meg and 50K MT pot..and put the one meg resistor back in..essentially like I did my volt meter..and calibrated as such.Its a great voltmeter!!

put the 1 ohm 5watt back in as prescribed and tried again and basically got the same results..just more complicated getting there.

I'm beginning to lean on a length of solid 12G copper wire roughly 1 foot to start..to try and construct a more stable solid shunt resistor..the process sounds extensive..however thats whats basiclly in my two digital meters.

Any Ideas greatly appreciated..
 

canadaelk

Active Member
A schematic of your setup, instead of all those words, would have been easier. One of the mistakes many people make with the 7106/7 is not realizing that the measurement ground is not the same as the IC common. E
 
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