Please see attachment this is electric
process heater, which have been widely used in many industrial application. Often we will apply one or more temperature sensors on surface of elements to
avoiding over temperature happened to damage the heater or fluid. So it is normal need we calculate the maximum temperature of element.

Of course if we set up the maximum surface temperature of elements act as my goal. I think it is very good if we use infrared temperature measure or thermal image measure.

However if we use one temperature sensor fasten to the elements, see second picture. How to set up my goal?  Thanks