b. GENERAL USES OF THE EQUIPHASE CELL
Standards laboratories throughout the world use triple point of water cells to derive the
zero of the International Temperature Scale. With its insulating jacket and cover, the
Equiphase Cell is ideally suited for this purpose.
While the ice bath will continue to find use as a temperature reference, mainly because of
its flexibility as to size, it should be compared to an Equiphase Cell whenever accuracy
and precision are required. The Equiphase Cell may be used to check the accuracy of the
ice bath by comparing the readings of a sensitive thermometer immersed in the ice bath
and then transferred to the Equiphase Cell. The resistance ratio should be 1.0000398 in
the case of a platinum thermometer. This ratio may vary by 1 digit in the least significant
figure (corresponding to .025 millidegree) for different thermometers. In the case of a
mercury thermometer, the difference in temperature should be +0.01,C.
The Equiphase Cell makes an excellent reference junction temperature bath for
thermocouples.
Convenience of the Equiphase Cell and its freedom from contamination suggest its use
also in less demanding applications. Accuracy can be assured with personnel who have
not had extensive training in the use of precision temperature standards.
c. PREPARATION. The Equiphase Cell should be placed on a laboratory bench in a
cleared area affording the operator sufficient room to lift the cover off and place it down
beside the cell. The following materials are required (See fig. 3).
(1) Solid carbon dioxide (dry ice).
(2) Alcohol such as methanol or ethanol.
(3) Thawing rod (supplied).
(4) Rubber insert for bottom of thermometer well (supplied).
(5) Thermometer which will fit into well. Well dimensions: 10 mm ID (3/8"), 35
cm long (14").
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