Cropico Thermocouple Potentiometer

Type P6



Instrument with millivolt scale in place


Housed in wooden box with thermometer


Two views of the interior



I was given this instrument which formed part of a collection of many instruments collected by Bob Evans by his daughter Alice Kirby. It was housed in a cardboard and plastic flip top case which was in a very poor state. When I opened it up I discovered that the battery was leaking and had caused extensive corrosion but standard cell  (Muirhead dated 1967) was fine. I decided that the case was beyond repair but discovered after repairing one of the resistors (340 ohms) that the instrument could be standardised with an old 1.5 volt cell but to use a new one giving over 1.6 volts it was necessary to increase the value of the resistor in series with the calibration rheostat from 75 to 133 ohms. I had an empty box which when cut down could be used to accommodate the instrument and its dials (see second picture above) The spacer used to take up the gap on the left hand side was used to mount a thermometer. The thermocouple which came with it, when heated with my soldering iron, gave a very nice deflection. The millivolt output corresponds with my digital voltmeters within 0.2 mV.