German Ohmmeter unknown make
ser no. 1389761

    









instructions on the rear for extending the range of the meter


 

scaleplate removed from defective meter

c

 interior of the switch section 

meter movement

Ex WW2 German ohmmeter 5 ranges from 1 ohm to 10 Mohm which had been taken apart and the meter section had been converted into a 0-120  (0-120mV) meter. The resistance selection had lost two knobs but otherwise was complete. The original scale had been removed and replaced with a hand calibrated one. I have married the two parts together and after some experimentation have discovered how it may have been intended to work. I made a new scale for the four lower ranges and fitted two replacement knobs. The unit takes two 1.5 volt cells which no longer seem to be available, they are shorter and larger diameter than AA cells.

Recently (2015)  I purchased an identical meter  which had an open circuit meter movement so I was able to use the scaleplate selector switch knob and resistor coil to put the original instrument back as manufactured.

For the low ranges the unknown resistance is connected to the black terminals and the left hand knob is turned clockwise until the pointer reaches the calibration point, the right hand button is then depressed and the reading multiplied by the appropriate constant as shown in the table gives the resistance. For the higher ranges (in red) with the right hand button locked in the depressed position, the meter is used in the conventional manner, shorting the terminals and adjusting for full scale deflection before connecting to the unknown resistance.

This is what I think is the circuit.