Telecom Laboratory Services used this Weston normal cell during the mid 20th century in association with other measuring instruments to monitor the quality of its telecommunications lines and ancillary equipment and to calibrate the field equipment used to measure telephone transmission equipment. The Weston cell might have been used until around 1990 and it wasn't producing a voltage when given to the Museum in 1993.

This is a high-quality standard electrical voltage provider made by a well-known English scientific equipment manufacturer.

Telecom Laboratory Services was a major Australian telecommunications quality control laboratory. The lab used the cell with other analogue electrical measurement instruments for much of the twentieth century before the conversion to digital electronic testing methods and fully digital telecommunication networks.

The standard cell is similar to those used in scientific research laboratories, industrial quality control facilities and university and technical training courses where precise electrical measurements were required. Although such chemical cells are still used to provide reference voltages, they have been, for the most part, replaced by stabilised electronic sources.

This is a type of standard cell, which is a battery that produces a precisely known voltage in laboratory conditions at 20 degrees centigrade.

Notes from Mike Turnbull, former Postmaster General's Department telecommunications technician: 'This a Weston cadmium saturated cell - also called a Weston normal cell, often shortened to simply the Weston cell (even though there were in fact two different types of Weston cell; the unsaturated cell, and the saturated cell). It was invented by Edward Weston (b. May 9, 1850, Oswestry, Shropshire, England d. August 20, 1936, Montclair, N.J., U.S.A.) in 1893. It is made up of a mercury impregnated cadmium (amalgam) anode, a saturated cadmium sulphate solution as the electrolyte, and a mercury impregnated mercury sulphate cathode. The Weston normal cell was adopted in 1908 as the international standard for the volt at the London International Conference on Electrical Units and Standards. Following the conference Weston waived his patent rights to the cell. It continued to be used as the international voltage standard until 1972. It delivers an open circuit electromotive force of precisely 1.0183 volts at 20°Celsius. This voltage varies with ambient temperature in a very predictable manner. In combination with a calibration graph and a thermometer (often built in to the top of the cell), the voltage at room temperature can be precisely determined. Any significant current drawn from the cell will cause the output voltage to change quite severely. Consequently, in practical use, the circuit in which the cell is employed is designed so that only an extremely small amount of current is drawn from the cell. Banks of Weston cells were used in conjunction with precision potentiometers (see Precision vernier potentiometer, Cropico, type P10, also from Telecom Laboratory Services) to precisely measure other voltages by comparing them with the cell voltages.'

The 'Cambridge Instrument Co. Ltd'. name was used between 1924 and 1967.

This cell was used by Telecom Laboratory Services, The Boulevard, Strathfield, Sydney, as an accurately known voltage source. It was used in association with a range of electrical testing instruments to monitor the electrical characteristics of the phone lines in Sydney. This cell no longer produces a voltage.

Weston normal cell (standard battery), glass / metal / cadmium sulphate liquid / mercury / mercury impregnated cadmium amalgam, made by Cambridge Instrument Co Ltd, England, [1924-1967], used by Telecom Laboratory Services, Strathfield, New South Wales, Australia, c. 1930-1990

This voltage reference has two battery cells marked 'A' and 'B'. Each cell consists of a sealed H-shaped glass vessel containing an electrolyte of cadmium sulphate, a pool of mercury (the positive pole of the battery) in the bottom of one side of the H and a cadmium amalgam (the negative pole) in the bottom of the other side of the H. Platinum wires fused though the lower ends of the glass make the electrical connections from the battery poles to the external terminals of the cell. The glass cells are wired to sheet metal for support with a layer of felt between the glass and the metal. The sheet metal is screwed to the circular [plastic] top of the unit. Four electrical terminals, two marked '+' and two '-' are on top of the plastic disk. A hole in the centre of the disk is used for inserting a thermometer to check operating temperature. The outer (presumably cylindrical) casing of the object is missing.

Made: 1924 - 1967


Used: 1930 - 1990

The top of the [plastic] disk is marked:
'CAMBRIDGE'
'INSTRUMENT Co. LTD.'
'ENGLAND'
(company logo) 'EED.1120' [inventory number from previous owner or department]
'WESTON NORMAL'
'CELL.'
'NP 54714'
'No L-15762'

2008/187/7

1924 - 1967

127 mm

90 mm