Does DCMI mean dc mA?

Question

I am working with a 60 year old schematic and test procedure. The latter refers to adjusting rheostats to "300 DCMI" or "between 100 and 130 DCMI". There are voltage and ammeters attached to different terminals. Typical usage in the document would be:

Adjust the rheostat RA for 50 DCMI indication on meter A1.

(Meter A1 in the drawing is in series with the signal, so it is almost certainly a current meter, but this is not explicitly called out.)

The procedure is rather vague, but I'm almost certain that it's referring dc mA. That said, the procedure was probably written by a British firm and I'm wondering if DCMI means something else entirely or if there are subtleties I'm not aware of.

Answer 1

In this context, I believe DCMI stands for "direct current moving iron", which is how the meter measures and displays the voltage or current measurement value. This book provides some more detail about these types of meters:

The current to be measured, in general, is passed through a coil of wire in the moving-iron instruments. In case of a voltage measurement, the current which is proportional to the voltage is measured. The number of turns of the coil depends upon a current to be passed through it. For operation of the instrument, a certain number of ampere turns is required. These ampere turns can be produced by the product of a few turns and large current or reverse.

And this article provides some additional diagrams and information that may be useful.

Without seeing the schematic or procedure, it will be difficult to confirm whether it means 300 mA DC (as opposed to 300 uA DC or 300 mv DC).