We are currently developing a medical device called infusion pump where we use a load cell within the device. AD8223 is used as the instrumentation amplifier with a gain of 1000. We finished our prototype and now carrying out radiated immunity tests. Since it is a life supporting device 10V/m is created at 3 meters within the anechoic chamber. At several frequencies like 1.1GHz, 1.52GHz and 2.17GHz the output of the amplifier increases more than 300mV which affects the device performance.
Please see the attached schematics. The length of the twisted cable which connects the load cell to the main board is 10 cm. Placing snap on ferrites on the cable helped but we could not get rid of the increase at the output.
- Load cell is a wheatstone bridge with each resistor is 1K.
- R6 is used for offset nulling.
- OUT1 and OUT2 are connected to the ADC inputs of the MCUs.
I would be glad if you could help us about the issue.