problem with analog multiplexer

[solace76]

Hello friends,
I recently designed an 8 channel rtd temperature indicator. I used a common amplifier and philips make 74hc4051's to switch between multiple 3 wire rtd's. Now I have a common current souce and and then an amplifier stage which feeds into a 12 bit adc, what happens is as the ambient temperature changes the Ron of the 4051 change and introduces a error in the temperature display. Is there a hardware/software work around to this problem, I am using a microchip microcontroller 16f72, is there a circuit that I can use to eliminate this or modify the circuit.
I do not want to go in for the analog devices mux/switches as they are very expensive out here.

Best Regards,
Solace76

 

[throwaway18]

A primative way to solve the problem is to put the circuit in a thermally insulated box with a heater (big resisor) and a temperature control circuit. Keep the whole circuit at a temperature that is allways above ambient eg 50degC

Perhaps you could add a sensor the measure the temperature of the 4051 and compensate in software.