Triometer "System Abrahamsohn" test meter in leatherette
covered wooden case housing 4 shunts and one series resistor.
Instructions (in German) are on the inside lid. This nice test meter
be used to measure volts, amps and (with an external battery) ohms by
reference to the printed table in the lid. The
basic moving coil meter with mirror scale has a 100mV 2mA movement.
There are two pushbuttons (one originally missing) to alter the
sensitivity. The shunts are ingenious, they can only be inserted one
way into the two lower terminals and when inserted a switch is operated
to alter the internal circuitry to enable the instrument to be used as
an ammeter. Have a look at one of my
other German meters. This model was first made made in 1931. Gossen
making the "Mavometer" in 1925 which offered much the same range of
measurements using shunts and voltage multipliers.
This was given to me in 2004 by Bob
Haslam whose father acquired it many years ago. I have now
replaced the missing pushbutton, repaired the switch contacts and
traced out the circuit diagram.