How to do a temperature uniformity survey of an online induction annealing furnace having a helical coil.

If it's an online annealing process with an induction coil that is helical, you need to do an optical measurement with a line of sight. If you do not have a line of sight, then the induction heating coil will need to be modified with some holes between the coil turns to be able to then look through to measure the temperature. If you can't even do that, then the only way would be to look at the output of the process. which means that when the rod exits the annealing process, you can measure its temperature. You can measure the temperature as it enters the coil and measure the temperature as it exits. and make sure that that is within a process window that you have established.