Instruction Manual

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Form 655 (04.13) ©SOR Inc.
Recommended temperature measurement procedure for switches used to sense
temperatures of liquids and steam with set points below 200°F:
 Use a liquid bath (ethylene glycol, water, oil, etc.) with sufficient circulation to provide a
uniform bath temperature and efficient transfer of heat from the liquid to the sensing bulb.
 Fully submerge the sensing bulb into the bath. Direct-mount sensing bulbs should be
submerged up to the bottom of the process connection threads.
 Locate the tip of the temperature measuring standard (thermocouple, RTD, etc.) at the
mid point of, and adjacent to the sensing bulb.
 Locate the sensing bulb and temperature measuring standard so that they do not touch
the sides or bottom of the bath or the heating and cooling coils.
 When the bath temperature is within 3°F of the set points, it is recommended that the
temperature of the bath be changed at a rate of 0.1°F per 5 seconds or slower.
 The minimum and maximum bath temperatures that the switch sees during testing
should be duplicated each time the switch is tested. It is recommended that the tem-
perature of the bath be changed from the normal operating temperature to the critical
set point and back to the reset. Do not overshoot the critical set point if the switch is
going to be cycled more than once during the test.
Recommended temperature measurement procedures for switches used to sense tem-
peratures of liquids and steam with set points above 200°F:
Recommended procedures for set points above 200°F are identical to those for set points
below 200°F with the exception of the bath used to test the switches. We recommend
either a circulated oil bath or a fluidized sand bath. The bath should be tested for uniformity
of temperature from top to bottom and side to side. If necessary, steps may be taken to
improve the uniformity of temperature, such as altering the air flow through a sand bath or
improving circulation or stirring.
Recommended temperature measurement procedures for switches used to sense air
or gas temperature:
Switches used to measure the temperature of air or gas should be tested in such a way that
it simulates the actual service conditions as closely as possible. Chances of measurement
error are much greater in air because of its poor thermal conductivity. Rate of change of
temperature, velocity of air flow, location of sensing bulb, and location of standard must
be duplicated as closely as possible for successive calibration checks to assure repeat-
able results. If the switch is being used as a room thermostat, the entire switch should be
placed in a test oven for calibration and testing. If only the sensing bulb is exposed to the
air or gas being measured, then only the sensing bulb should be inserted into the oven or
test apparatus for calibration and testing. In this case the switch housing should be kept at
room temperature.