Cambridge Instruments pattern T meters

No.L-1788317 and L-128442

Cambridge Instruments pattern T meters Housed in polished wooden boxes. Moving coil instrument with additional scale and terminals for measuring alternating current in conjunction with a thermal junction. Scaled 0-150 millivolts at 500 ohms and 0-150 degrees [x 0.02] at 10 ohms. Note the Working. Cambridge Instrument Company Ltd, UK, date unknown.

This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt

Interior of the instrument

The meter is shunted by one resistor and wired in series with a 1.5 ohm resistor to present 10 ohms to the terminals on the left, the right hand resistor is 490 ohms thus presenting 500 ohms to the millivolt terminals on the right. A typical Cambridge vacuo junction is pictured below [this one is open circuit and does not belong to this meter]

Cambridge vacuo-junction