Evershed and Vignoles Serial Number 1980970
Bonding Tester Made by Evershed and Vignoles for Royal Airforce (part number 5G/6625-99-109-7544) The instrument is housed in a wooden box with sockets for two probes and a compartment for a rechargeable alkaline cell. The meter movement has two deflection coils and is similar to that found in insulation testers made by this firm see: megger though in this case a large current provided by a rechargeable alkaline cell is passed through the circuit to be tested and one deflection coil and the voltage developed across the circuit is applied to the other. The instrument can measure from zero to 0.1 ohm
Colin Ferrier who was an aircraft electrical fitter in the RAF has told me that the bonding tester was used quite frequently to check earth bonding of aircraft, particularly following fitment of new metal parts to aircraft ( ailerons, radio trays etc).
View of interior from below showing probe sockets and battery compartment
Note that there are what appear to be low value resistors (about 0.01 ohms) in series with each core of the probe leads. What are they for?
Probe and lead 5G/5207
The two core cable is terminated with low resistance wire wound resistors which are soldered to the substantial probe all housed black bakelite handle. Unfortunately I have only one probe and have made myself another but I do not know the function of the resistors or their supposed values.Nevertheless I have tried it with an alkaline cell and my homemade probe and have determined that instrument works.
