a plunger to the switch arm. The moving contacts are
switches. However, temperature switches can also be
normally closed switches. A basic temperature switch
located on this arm. A fixed contact maybe arranged so
contains a bellows or a diaphragm that works against an
the switch will open or close on a temperature rise.
adjustable spring. The spring causes the electrical
contacts to open or close automatically when the
operating temperature exceeds a specified value. The
bellows or diaphragm motion is produced by a sealed-in
gas that expands with rising temperature. The sensitive
Routine maintenance performed on temperature
element containing this gas may be built into the switch
switches should be accomplished according to PMS.
or located in a remote space and connected to the switch
The routine maintenance procedures performed on
by a capillary tube. A permanent magnet in the switch
temperature switches are the same as those discussed for
provides a positive snap when the contacts are opened
p r e s s u r e switches. Routine maintenance includes
or closed. This snap action prevents excessive arcing at
inspecting the switch for damage, corrosion, and proper
the contacts. The design of the switch allows movement
operation. The procedures for adjusting the switch were
of the contacts to determine whether the switch opens
discussed earlier in this chapter. The only difference is
or closes on a temperature rise. The switch is normally
enclosed in a metal case with a removable cover. The
the test setup you will use to calibrate the switch.
metal case provides a temperature-sensing port and an
The Navy uses several different pieces of equipment
electrical connection point. The temperature at which
for calibrating heat-sensing devices. There are also
the switch operates is adjustable.
several methods for calibrating temperature devices.
The King Nutronics, models 3604 (fig. 6-9, view A) and
3605 (fig. 6-9, view B), are portable temperature
The operation of the temperature switch is basically
t h e same as that of the pressure switch. In fact,
solid-state, digital technology for the Navy. The model
temperature switches are actually operated by changes
3604 is used to calibrate temperature control devices
in pressure. The temperature element is arranged so a
within a range of 100° to 1199°F. The model 3605 is
change in temperature will cause a change in the internal
used to calibrate temperature control devices within a
pressure of the sealed-gas or air-filled bulb or helix that
range of -40° to +250°F. Usually, temperature switches
is connected to the actuating device by a capillary tube.
on gas turbine-powered ships are calibrated at regular
A temperature change will cause a change in the volume
intervals by a calibration team. If a switch malfunctions,
of the sealed-in gas. This, in turn, will cause movement
it is removed and sent to a calibration lab for testing.
of the bellows or diaphragm. The movement is sent by
Figure 6-9.--King Nutronics. A. Model 3604. B. Model 3605.