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Instrumentation Amp

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Sceptre

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hey guys...i'm new to the spot...i've been at a project here at work for like 3 days and i'm starting to get annoyed with it. i had a circuit working before, but switched around a couple things and now can't get it to work

it's an AD623 (simple in-amp). simply put, i am putting in 0-5v and trying to get out 0-10v. I'll try to explain what i have setup and see if anyone can help me. i have a DAC chip going from 8bit to analog (works perfectly). i am using the instrumentation amp to amplify signal as pneumatic valve i'm using is 0-10v.

The chip is 8-pin
-- Pins 1 & 8 are +Rg and -Rg..they are connected with a 100k resistor (x2 multiple)
-- Pins 2&3 are inputs + and -...i have one coming from my DAC and one to ground (ground point i use is same as DAC ground).
-- Pins 4&7 are inputs (10v from external supply)....i have bypass caps setup off the input 10v. 0.1uF and 10uF going to earth ground (separate ground)
-- My reference pin also goes to earth
-- the last is my output pin


right now i'm confused.....if i take a reading iwth my multimeter between output and ground then i get the in-amp outputting from 0-4.3v.
if i take a reading between output and (-) of 10v supply then i get output swinging from 9v to 9v with 0v and 5v input respectively. also, it is perfectly linear as when input is 2.5v, the output is 0.00v

i'm lost...anyone got any ideas???


thanks a million guys.




Nick
 

mechie

New Member
DAC with Instrumentation amp

Any chance of a circuit diagram ?
Can you clarify what supply voltages are where and how the earths are connected.
 
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