Kelvin and Wheatstone bridge, metal / wood / plastic, made by H W Sullivan Ltd, London, England, 1955, used by Defence Standards Laboratory, Adelaide, South Australia, c. 1960-1977, and CSIRO, Woodville North, South Australia, c. 1977-1990
A Wheatstone bridge can be used to measure resistance by comparing an unknown resistor against precision resistors of known value. A Kelvin double bridge is a variant of the Wheatstone bridge and used for measuring very low resistances. This Kelvin and Wheatstone bridge design enables measurement of both high and low resistances. It can measure electrical resistances from 1megohm to one-hundred thousandth of an ohm with high accuracy when used with a sensitive galvanometer. This device is an example of a highly accurate resistance measurement device for the period 1950-1980. It was replaced by more accurate and easier to use digital measurement equipment.
It was used by the Defence Standards Laboratory, Adelaide, South Australia, c. 1960-1977, and CSIRO Woodville North, South Australia, c. 1977-1990. It may have been used at the CSIRO laboratory as part of their equipment to calibrate the temperature readings of platinum resistance thermometers.
A Wheatstone bridge can be used to measure resistance by comparing an unknown resistor against precision resistors of known value. A Kelvin double bridge is a variant of the Wheatstone bridge and used for measuring very low resistances. Its additional complexity over the basic Wheatstone design avoids errors otherwise incurred by stray resistances along the current path between the low-resistance standard and the resistance being measured.
This Precision Kelvin and Wheatstone bridge described in the abridged edition of the 1959 H.W. Sullivan Ltd, London catalogue entitled Electrical Standards for Research and Industry Testing and Measuring Apparatus for Communication Engineering p185
'PRECISION KELVIN and WHEATSTONE BRIDGE
0.1 micro-ohm to 1 megohm¬?
This combined Kelvin and Wheatstone Bridge has been designed in response to many requests which we have received from users of our Wheatstone bridges. It has an exceptionally wide range- as a Wheatstone Bridge it may be used for measurements to 0.02 per cent. accuracy from 1 ohm to 1 megohm and as a Kelvin Bridge for measurements of two or four terminal resistances by the four terminal method from 10 ohms down to 0.1 micro-ohm with an accuracy of 0.03 per cent, or 0.03 micro-ohm whichever is the greater, the ultimate subdivision being 0.01 micro-ohm.
Manganin coils of 0.01 per cent. accuracy are employed in the bridge and four low resistance standards of 0.03 per cent. are incorporated, their resistance values being 0.1. 0.01, 0.001 and 0.0001 ohm.
The bridge is designed to permit the use of heavy currents (up to 100 amperes) for low resistance measurements, the battery key being especially designed to deal with currents of this order.
The switches, both plug and rotary, are of the finest design and construction and, together with the reliable and permanent resistance work, will ensure an extremely long and accurate life of heavy duty.
The accuracy is the best obtainable and so the bridge may be used for the determination of conductivity. We shall be pleased to quote for complete equipment for such measurements upon request.
List No. T1080.-Combined Kelvin and Wheatstone Bridge, as described ¬? ¬? ¬? ¬? '.
H.W. Sullivan Ltd also produced a second grade Kelvin and Wheatstone Bridge, however the company usually engraved (SECOND GRADE) on any lower quality instruments, perhaps this object is the higher quality bridge. Also, this bridge looks identical to the one shown in the catalogue next to the Precision bridge information. While the second grade bridge's design is not shown, in other cases where a second grade instrument is available, the design of the second grade instrument shown in the catalogue is different from that of the precision instrument.