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G
Mounting and Installation
Scheme
Normal
1
operation
Danger
0
of frost
cold
FUNCTION
The switch inside frost protection thermostat FST responds (closes contact C - 2) when temperature falls below the
preset temperature setpoint over a capillary tube length of at least 40 cm. Simultaneously contact C - 3 breaks and can
be used as a signal contact. Resetting (closing contact C - 3) happens automatically when temperature rises above the
preset setpoint value again (on type FST - xR resetting must be done manually by pressing the reset button).
The FST is "intrinsically safe", i.e., in the event of damage to the capillary tube-membrane system, it automatically
switches to the heating function. Contact C - 2 closes and therefore can be used as operating contact. The air tem-
perature is detected over the entire sensor length (capillary tube). The gas-filled (R 507) membrane system and the
capillary tube constitute one measuring unit, which is mechanically coupled to the microswitch.
Capillary tube: The capillary tube is laid uniformly at the hot side of the air heater to be protected (in case of air coolers in
front of the air cooler) at a distance of approx. 5 cm crosswise to the heat exchanger tubes over the entire area. For test
purposes, it is recommended to make a loop of approx. 20 cm directly underneath the enclosure and before entering the air
duct. To avoid damaging the capillary tube, a minimum bending radius of 20 mm must be observed. Installation is facilitated
by using the mounting clamps available under accessories.
Frost simulation: The frost situation can be simulated and functioning of the device can be tested by dipping the capillary
tube testing loop into a pot filled with ice water.
Mounting diagram
SD
T
w
warm
FST
Connecting diagram
C
2
3
C
C
2
2
3
FST
Notes regarding FST
A preset setpoint value can be lead-sealed at the adjusting
screw. It is absolutely necessary to ensure that ambient
temperature at the device does not drop below the preset
setpoint temperature.
This device must be operated in a non-precipitating pollutant-
free ambience.
Rev. 2017 - V22 GB
FST
3
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