Fluke 1552a, 1551a User Manual
1551A Ex/1552A Ex
Immersion Characteristics
Instruction Sheet
Introduction
The 1551A Ex/1552A Ex Stik Thermometer (Theremometer)
must be adequately immersed in the medium to make an
accurate temperature measurement.
Immersion Depth
The minimum required immersion depth depends on the type of
medium (whether wet or dry) as shown in Table 1. These figures
should result in immersion errors of less than 0.005 °C in most
cases. Actual results can vary depending on the type and form of
the surrounding materials.
Table 1. Immersion Depth
Medium Minimum Immersion Depth
Wet (liquid bath, thermowell with
thermal compound)
Dry (dry-well, thermowell without
thermal compound)
7 cm (2.8 in.)
12 cm (4.8 in.)
Time Constant
The different probe sizes of the Thermometer exhibit different
settling time constants. This parameter describes the time it
takes for the Thermometer to change 63 % toward its final
temperature (see ASTM E 644).The time constant is primarily
dependent on the diameter of the metal sheath of the
Thermometer. Typical approximate time constants are given in
the following table.
Table 2. Time Constant
Sheath Diameter Time Constant
4.8 mm (3/16 in.) 14 seconds
6.35 mm (1/4 in.) 21 seconds
November 2010
© 2010 Fluke Corporation. All rights reserved.
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