Ferranti DC Test meter in black Bakelite case housing an eight range 1000 ohms/volt moving coil voltmeter [100mV to 250V FSD and an eight range moving coil ammeter [10mA to 25A]. This instrument is in poor condition. One of the dial type knobs is missing as are five of the terminals. The glass for the voltmeter was absent and I have replaced this with a piece of perspex. The meter movements appear to function, I have discovered that only two of the multiplier resistances are OK. The label on the lid has the patent number 285633 which was granted in 1928. Date probably 1929/30 Ferranti UK
This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt.
This instrument is illustrated on page 398 of "Electrical measurements and Measuring Instruments" by EW Golding, Pitman 1935. Golding remarks that " owing to their adaptability to extension of range by shunts and multipliers, two permanent magnet moving coil instruments are frequently mounted into a single case which also encloses the the necessary shunts and series resistances to cover a wide range of current and voltage. Two dial switches are usually fitted to enable the ranges of the two instruments to be changed conveniently as required. The whole constitutes a "test-set"and is a very useful piece of apparatus for resistance and other measurements in which a very high degree of accuracy is not required."
Using this instrument to measure resistance would be rather tedious and require some calculation.
View of meter with front cover removed
This is what it should look like!
Neil Bousfield came across this
page when looking up for some information on Ferranti as he has a pile
of brochures on their equipment from the early 30's. He has a complete
example of this item as well as the brochure/catalogue on it dated
about 1931 or 1932 which I have reproduced (PDF file) here.
And this is what it looks like when the lid is closed.