Fenwal Industrial Controls
Category: Temperature Controls
SERIES 17000, 18000
THERMOSWITCH® Temperature Controllers
• Fast response
• Close control
• Extreme sensitivity
• Vibration resistance
• Hydraulic Laminating Presses
• Livestock Watering Fountains
• Label Adhesive Applications
• Paint Drying Equipment
• Hot Stamp Printers
• Vending Machines
• Deep Fat Fryers
• Textile Platens
THERMOSWITCH® controllers control temperatures as
low as -100ºF (-73ºC) and as high as 600ºF (316ºC) with
the proven dependability of over 70 years of service to
PRINCIPAL OF OPERATION
The THERMOSWITCH® controller is a strut-and-tube type
thermostat comprised of two basic parts: the outer shell,
made of high-expanding metal and the strut assembly, made
of low-expanding metal.
A pair of electrical contacts is mounted on the strut assembly
and installed in the shell under tension or compression.
Since each end of the strut assembly is mechanically
connected to the ends of the shell, a net change of force
is produced on the strut assembly as the shell expands or
contracts with changing temperature. The temperature at
which the contacts “make” or “break” can be regulated by
a temperature adjusting sleeve.
This adaptation of the differential-expansion principle gives
several important control advantages:
• Fast Response
Since the outer shell of the THERMOSWITCH® is the
active sensing member, and not merely a housing, response
to temperature change is almost instantaneous.
• Close Control
The controller’s shell and strut arrangement has “anticipation”
characteristics which substantially reduce the amount of
overshoot and undershoot during conditions of rapid
temperature change. Anticipation is produced by an inherent time
lag between the shell and struts, which causes the shell
‘to “lead” the struts by an interval that varies with the rate
of temperature change. With rapid temperature rise, the shell
exerts a larger net force on the struts and tends to pull them
apart sooner than if the temperature were rising slowly.
The result is several degrees or more of anticipation which
helps produce closer control.
• Extreme Sensitivity
The strut and contact assembly operates by slow make and
break. This means that every temperature change, no matter
how small, causes a corresponding change in the space
between the electrical contacts. Therefore, contact action
can be produced by a very small temperature change,
which accounts for the THERMOSWITCH® controller’s
excellent resolution sensitivity of 0.1ºF (0.05ºC).
• Vibration Resistance
Since the strut assembly is assembled under tension or
compression, a properly installed unit has excellent vibration
resistance and will provide the best possible control under
difficult physical conditions.
• Agency Approved
Various models are listed or component recognized
by Underwriters Laboratories (UL) and certified by the
Canadian Standards Association (CSA).
Replaces Part Numbers: 01-017002-000, CAR01-017002-000