On bulk milk tanks with evaporator plates in the belly of the tank, where is the temperature sensor and where are the thermostats for the compressors?

Also, how are multiple compressors for a bulk tank typically operated? With a tank that has two compressors, for example, with two separate evaporator plates, is it typical for both compressors to have the same setpoint? Or would they be staged, so one came on at say 38oF and another at 40oF if the load was too much for just the first to maintain 38.

Thanks in advance for your help.