Fluke 1551A Ex 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.
Wet (liquid bath, thermowell with
thermal compound)
Dry (dry-well, thermowell without
thermal compound)

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.
Sheath Diameter
4.8 mm (3/16 in.)
6.35 mm (1/4 in.)
November 2010
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1551A Ex/1552A Ex
Immersion Characteristics

Table 1. Immersion Depth

Medium

Table 2. Time Constant

Fluke-Direct
Instruction Sheet
Minimum Immersion Depth
7 cm (2.8 in.)
12 cm (4.8 in.)
Time Constant
14 seconds
21 seconds
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1.8