The device that I had problem with is a 16 channel, PID controlled, hot-runner temparature controller that I developed a year ago. It is mainly used at plastic injection sector and provides almost perfect temperature control in between 0-400 C. (the controller is 89C55WD)

Front end chip is 2x16 channel MUX (I had first tried 16 chan. ADC but it coused a lot of problem such as offset adjustments, instability etc.) and then simple opamp (LM358) just for voltage multiplication of 82 and then a single channel ADC (ADC0801 or 804 is a single channel and 8 bit but by means of a trick I could used it as if it was 9 bit)
The only so called noise protection I have used is a 100nF cap between the thermocouple - and + terminals.

With this spesifications device works several weeks with absolute satisfaction until it blows up. The damaged parts are MUX and subsequent opamp only.

If that much detail is not enaugh please email me

rustu@netas.com.tr

The readers may not be interested any longer.

Rustu