Thank you Gary. That is a great response.
Ondercin, a few other notes of importance.
1) On the FMD88-10, ADC #1-6 are high impedance with no internal pull down resistors, whereas ADC #7-8 are pulled down to 0V via on-board 20k resistors.
2) Since ADC channels 1-6 are all high impedance, they will float high when disconnected. In order to reduce the effects of electrical noise, we recommend that you connect any of these unused inputs to common (0V).
3) Since ADC channels 7-8 are internally pulled down via 20k resistors, you will need to follow the recommended resistor wiring in section 5.2.2 of the FMD88-10 user manual when interfacing to 4-20mA analog sensor signals. I would recommend using any of channels 1-6 instead so that the resistor wiring is simplified.
4) If you follow Gary's recommendation to use 0-10V sensor outputs, then it will be easier to use ADC #7-8 for the voltage divider since you only need to add a 20k resistor in series with each of the two ADC inputs. You would then need to add a full 2 resistor voltage divider for the 3rd sensor that would connect to any of ADC #1-6 since these do not have any internal pull down resistor.
5) Adding software filtering is highly recommended. If you want to apply some simple software filtering first, you can use the following to take the average of 100 readings on each ADC channel you are using.
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FOR I = 5 TO 7
A = 0
FOR J = 1 TO 100
A = A + ADC(I)
NEXT
DM = A/100
NEXT
-----------------------------
This will store the averaged ADC readings in DM[5] to DM[7] corresponding to ADC(5) to ADC(7). The above code takes about 35ms to execute, so there is plenty of time to take new averaged readings every 100ms (assuming the rest of your program is not overly large and doesn't contain delay statements).
I'm sure Gary's software will provide more sophistication, but the above code will help a lot.