I'm making a thermocouple based temperature controller. The thermocouple voltage is measured by using cold junction compensation IC LT1025 and precision opamp LT1050.
The measurements are read by ADC and the relay is switched on by a MOSFET controlled by microcontroller.
The device will be a separate "shield" containing cold junction compensation, opamp, MOSFET and connectors for thermocouple and relay.
I want to avoid noise on analog part as much as possible and I'm using separate ground for analog part – grounds for analog and digital parts will be connected on power supply (which might cause some problems in ADC reading accuracy as these grounds will be at different potential, but I will compensate that in software) and I'm running a trace, separate from analog ground plane, for relay ground return.
I've put a reverse protection diode across relay terminals and decoupling capacitors of values 10uF and 100nF on MOSFET Drain terminal. What else should i do to avoid spikes from relay in my analog part? It might be not too critical in this particular application, but I'm willing to learn.
Circuit diagram that Olin is slightly less liable to complain about: