What kind of meter would you use to detect a ground in the armature coils?

To detect a ground in the armature coils, an ohmmeter is the most appropriate tool because it measures resistance. When testing for ground faults in armature coils, the ohmmeter can help determine if there is an unwanted connection between the coil windings and the ground. If the resistance measurement shows continuity to ground (i.e., a low resistance value) when there should be none, it indicates that a grounding issue exists.

This method is effective because a properly functioning armature coil should not have any electrical continuity with the ground. By using the ohmmeter, you can evaluate whether the insulation of the coils has failed, thereby revealing potential problems that could lead to electrical shocks or equipment malfunction.

The other instruments mentioned serve different purposes: a voltmeter measures voltage, which is not useful for ground detection, an ammeter measures current flow, and a frequency meter analyzes signal frequency, but none of these would provide the specific resistance measurement needed to identify a ground in the armature coils.