OK, maybe my question and problem are naive but i need to ask anyways....
I have an application using two 32:1 ADG726 analog muxes. The whole purpose is to compute the unknown resistance load on mux inputs by simply injecting a known current and measuring the voltage (after appropriate gain scaling) to compute the resistance on my inputs.The unknown resistance values could vary from 1 ohm to 10,000 ohms. I use the two ADG726 muxes in a differential arrangement to measure the many known loads(up to 32) at the mux inputs.
As long as all unknown loads are connected to the muxes, i have no issues. The problem is that i need to detect when a load is open or absent on any channel w/o affecting the reading accuracy on the rest of the loaded channels. I notice that if I have a load on channel 1 and none for the rest (2 - 32), I get bogus readings for the these unconnected channels(due to leakage current?) and the customer is very unhappy with this problem. In his mind, if a channel is open, it shouldn't display any bogus voltage at all. Unfortunately, these bogus voltage readings are well within the valid range for normal voltages. He doesn't understand why a bogus resistance value is displayed for an unconnected channel...
How can i get rid of these voltages on unconnected channels. I cycle through each mux channel every 80 uSecs. I know unused inputs are supposed to be tied to ground or Vdd but i don't have that option.
Again each channel will have a valid load on it but i need to detect when that load is disconnected due to a blowup or simply when the customer needs to use less than 32 resistive loads for a particular run. The number iof loads varies on a day to day basis. He just doesn't want bogus data to show up on those unused mux channels. Any help would be greatly appreciated.
The actual application uses 6 ADG726s for a total of 192 resistive loads to be measured but i limited the above discussion to 32 loads using two muxes for simplicities sake