I work at a Nuclear power plant. The rod control system works using a stack of very large coils to withdraw and insert the control rods. During the current refuel I've been working on, our vendor had recommended changing our procedures for testing. We used to just perform resistance and insulation resistance(meggar) checks. The vendor stated that resistance is not a good measure of coil degradation and we now also perform an inductance check measured in "henrys". We had previously had 2 upper gripper coils fail that had previously passed resistance checks after appearing noisy on our coil current monitoring equipment. During this refuel we had a coil pass resistance checks per our procedure but fail the new inductance checks. This coil was replaced. Now that I've bored you with that. Could this information possibly help troubleshoot a weak acting coil that otherwise seems fine because you checked the resistance per the manual and called it good? I haven't seen a database that gives an acceptable range of measurements for the various coils that are in pinball machines. I guess you could get baseline data from a brand new coil to compare to.

Not at work, currently on nights. Understand the resistance check is to look for a short. Just curious if coil degradation can be seen on an inductance check with small pinball coils. Just my own curiosity. As a side note our coils are used to control reactor power. To safely shutdown they just need to fall in. So unless gravity stops being a thing, I assure you it is very safe.