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 megohmÂ?

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 Â? Â? Â? Â? '.

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.

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

This is a plug and decade rotary-switch design bridge. The bridge is encased in a rectangular wooden box. The upper third of the face of the bridge has a [wooden] surface on which are two sets of one long and one short brass blocks. The upper set of blocks is engraved 'DIVIDING RATIOS / KELVIN AND WHEATSTONE' and 'STANDARDS', the lower 'DIVIDING RATIOS KELVIN / OR MULTIPLYING RATIOS WHEATSTONE'.

Adjacent to each set of blocks are thirteen plug-type brass receptors, which are marked '0.0001', '0.001', '0.01', '0.1', (each with larger plug holes to connect with the shorter brass blocks), '1', '10', '100', '1000', 'WHEATSTONE', with four unmarked in each set (each with smaller plug holes to connect with the longer brass blocks); four pairs of brass terminals labelled 'GALVO', 'BATTERY', ' P1 P2 UNKNOWN' (resistance) and 'WHEATSTONE UNKNOWN' and two terminals labelled 'C1' and 'C2' [perhaps for compensating leads]. There are three large and seven small [ebonite] topped brass plugs.

The lower two-thirds of the face is covered with a grey metal plate on which are four black [ebonite] dials labelled 'HUNDREDS', 'TENS', 'UNITS', 'TENTHS' each with a small circular [glass] covered opening to the lower left to read the numerical setting of the dial. There are two [ebonite topped] tap keys labelled 'BATTERY KEY' and 'GALVANOMETER KEY'. There is also an [ebonite topped] multiposition dial or switch labelled 'GALVO SENSITIVITY'.

Made: 1955

Engraved into the top middle of the metal surface of the instrument in black is:
'KELVIN AND WHEATSTONE BRIDGE
IN OHMS (ABSOLUTE)
SERIAL No. 2753/1955
H.W.SULLIVAN Ltd LONDON'
Engraved into the middle of the metal surface of the instrument in black is:
'MULTIPLYING RATIOS KELVIN
OR
ADJUSTABLE ARM WHEATSTONE'
Engraved into the lower left of the metal surface of the instrument in black is:
'TO CLEAN SWITCHES
PULL OFF SWITCH KNOBS
AND REMOVE THIS PANEL.'
Laminated plate affixed to side of wood box engraved with 'P.U. 28583'

Punched in the wooden bottom of the object is

'TS 23797'

Also on the bottom is the letter F, inscribed in pencil on the left hand side.

Sticker on side of unit;
'THIS EQUIPMENT IS THE PROPERTY OF
COMMONWEALTH OF AUSTRALIA'
over which is is a paper sticker typed:
'C.S.I.R.O.
NM 48'

2008/174/4

1955

210 mm

400 mm