Annex B
(Mandatory)
Determination of the Mean Depression of Zero of Thermometers
B.1
It is not possible to determine the depression of zero of clinical thermometers (mercury-inglass, with maximum device) covered by this Recommendation. Therefore, special test thermometers (Clause B.2) must be manufactured from the glass being examined in order to conduct the necessary measurements. The following provisions must be observed in manufacturing the test thermometers and conducting the measurements.
B.2
The test thermometers must meet the following requirements
B.2.1
Scale range: at least from to .
B.2.2
Scale interval: , or .
B.2.3
The scale spacing must be a least for enclosed-scale thermometers and at least for solid-stem thermometers.
B.2.4
The expansion chamber must be large enough to allow the thermometers to be heated to without damage.
B.2.5
The thermometers must be properly stabilized by the manufacturer and must meet the requirements of the stabilization test (Clause B.3).
B.3
The proper stabilization of each test thermometer must be tested in accordance with the following provisions:
B.3.1
The thermometer is heated in a test bath (liquid bath or metal block type oven) from ambient temperature up to and kept at this temperature for at least five minutes. It is then cooled to in the test bath, which decreases in temperature by to .
B.3.2
When the thermometer has reached a temperature of , it is removed from the test bath and its correction (value ) is determined (A.1.2.2.5).
B.3.3
The thermometer is then heated a second time to in the test bath and kept at this temperature for 24 hours. It is then cooled to , as before (B.3.1).
B.3.4
When the thermometer has reached a temperature of , it is removed from the test bath and its correction (value ) is determined once more.
B.3.5
must not differ from , by more than . Thermometers which do not meet this requirement must not be used to determine the depression of zero.
B.4
The mean depression of zero is determined in accordance with the following provisions:
B.4.1
At least three test thermometers must be used. They must be manufactured from the glass being tested, have met the requirements of the stabilization test (Clause B.3), and not have been heated above the ambient temperature once value has been determined (B.3.4).
B.4.2
Each of these thermometers must be tested at least three times in accordance with the provisions of B.4.2.1, B.4.2.2 and B.4.2.3 below.
B.4.2.1
The thermometer is kept in a test bath at for 30 minutes. It is then removed from the bath and allowed to cool in air. While it is cooling to ambient temperature, its bulb must not come into contact with other objects.
B.4.2.2
The correction of the thermometer is determined not later than 15 minutes after the thermometer has been removed from the test bath. The correction value obtained is designated by the symbol .
B.4.2.3
The thermometer is then kept for one week at a temperature between and . At the end of the week the correction is determined. This correction value is designated . The procedures described in B.4.2.1 and B.4.2.2 are then repeated, and a correction value, designated , is obtained.
B.4.2.4
The procedures described in B.4.2.3 are repeated to obtain a series of differences , , . These are the values of the thermometer’s depression of zero from the first, second and -th series of measurements, respectively.
B.4.2.5
When series of measurements have been made with test thermometers, the following expression is obtained for the mean depression of zero of these thermometers:
which must not exceed (4.1).
In accordance with the provisions of B.4.1 and B.4.2 , the conditions
must be met for and , and the standard deviation of the mean depression of zero determined in accordance with the aforementioned provisions, must not exceed .
B.4.2.6
If a more accurate value for the mean depression of zero is required, at least five series of measurements on at least five test thermometers must be carried out.