veryADD
Newbie level 5
Hello, clueless newbie here
I'm trying to assemble a simple instrumentation amplifier for a school project and frankly i could use some help. Im using a simple 3 op-amp schematic (in the picture 1) with a following resistor configuration R1=R2=R3=22k, Rgain = 10k . According to my calculations this should yield a gain of 5.4.
For testing the circuit i hooked 1k and 10k resistors in series to a 9V battery and measured V1 from before the 1k resistor and V2 after the 1k resistor. Again acording to my calculations the the differential voltage should be Vd=0.82 and thus the output of my instr.amp should be 4.4 V. When i first tested the circuit i kept getting 0.6V as output. I also discovered that i could change voltages V1 and V2 and output would still remain in 0.6 V !. I reassembled the circuit many times just making sure i hadnt made a mistake, problem didnt go away. Next i thought i might have a bad batch of op.amps and i swapped the LM385N for a more sexy TLC27L2CP. Now the output voltage switched from 0.6 to 0.01 but still not the correct value. Why wont my amplfier do what its supposed to? :'(
One more thing! I also disconnected the first two amps and the resistors R1s, Rgain. I then proceeded to test the differential amplifier part alone and apparently that works as expected.
I realize that without seeing how i actually wired this thing on my breadboard its hard to say where i screwed up. Im just hoping for some general pointers. I'm also worried there is something fundamentally flawed in my testing setup (like i'm not 100% sure you can even measure a differential DC voltage with a instrumentation amplifier, please verify this
).
Thanks in advance.
I'm trying to assemble a simple instrumentation amplifier for a school project and frankly i could use some help. Im using a simple 3 op-amp schematic (in the picture 1) with a following resistor configuration R1=R2=R3=22k, Rgain = 10k . According to my calculations this should yield a gain of 5.4.
For testing the circuit i hooked 1k and 10k resistors in series to a 9V battery and measured V1 from before the 1k resistor and V2 after the 1k resistor. Again acording to my calculations the the differential voltage should be Vd=0.82 and thus the output of my instr.amp should be 4.4 V. When i first tested the circuit i kept getting 0.6V as output. I also discovered that i could change voltages V1 and V2 and output would still remain in 0.6 V !. I reassembled the circuit many times just making sure i hadnt made a mistake, problem didnt go away. Next i thought i might have a bad batch of op.amps and i swapped the LM385N for a more sexy TLC27L2CP. Now the output voltage switched from 0.6 to 0.01 but still not the correct value. Why wont my amplfier do what its supposed to? :'(
One more thing! I also disconnected the first two amps and the resistors R1s, Rgain. I then proceeded to test the differential amplifier part alone and apparently that works as expected.
I realize that without seeing how i actually wired this thing on my breadboard its hard to say where i screwed up. Im just hoping for some general pointers. I'm also worried there is something fundamentally flawed in my testing setup (like i'm not 100% sure you can even measure a differential DC voltage with a instrumentation amplifier, please verify this
).Thanks in advance.
