According to this circuit, my current will stay at a constant 1.41mA given an input of 1Vp. I get a stable current until my Load Resistance R8 goes above 6k ohms, then it starts to drop.
My questions are -
1) Is there a way to increase my Load Resistance R8 above more than 20k ohms, while obtaining a constant current of 1mA, without changing the op-amp used. [I have tried increasing Vin, but it doesn't work]
2) I have rebuilt this circuit on an actual circuit board, but my results that I obtain vs the simulation are totally different. According to this circuit, above 6k~7k ohms, I would obtain a saturation (squarish) waveform of +11V -to- -1V in the oscilloscope at the probe 4 connection as shown below in image 2. However, in my actual connection, I am only obtaining a 2Vpp sinewave across that same point for a 10k ohm connection. I have changed the IC chip and still obtained the same issue. I was wondering if anyone knows why such a different result is obtained from the simulation.
This project is based on the Electrical Impedance Tomography Design. I have to build a constant current source that outputs a 1mA(rms) current across a body(tank) of water. I have built this circuit, but it does not seem to work according to how I hope it would. If you have any ideas or alternate circuit designs to suggest, I am open to listening also.