Serial No. AL 97141
Sangamo Weston Polyphase Watt meter 0-750 Watts in three ranges FSD housed in a wooden case with calibration certificate in lid. Now working. Date January 1960. Enfield, London.UK.
This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt.
Well made case with later carrying handle
Calibration certificate dated 1960 is in the removable lid.
Two views of the resistor banks note that each bank has a 50 ohm bobbin resistor in series with the switch connection.
Many of the resistors were open circuit
Tis instrument which was once owned by Bruce Peebles has needed many hours of work to get it back into working order. The actual breaks in the resistance wires proved to be impossible to locate visually. I gently sanded one edge of each faulty unit and used an ohmmeter to locate the breaks [some units had several] and then scraped away the varnish and soldered fine wire across the faults and protected the joints with nail varnish. Inevitably the resistance of the repaired units was some what less than the figures given on the calibration certificate. This was rectified by adding low value wire wound resistors in series/parallel with the bobbins after re-assembly. I used my Cambridge resistance bridge to check the finished values.
Edward Weston [1850-1936] founded the Weston Electrical Instrument Company and held 334 patents. You will find information about Sangamo in this link as well.