High Country Tek HFS - Manual (Page 7)

Hydraulic Fan System Controller: HFS
Two wire NTC thermistors sensors with both wires brought back to the unit are
required for each zone being monitored.
DO NOT use thermistors with one lead grounded as the sensor and the measuring
accuracy will be severely degraded !
The controller is compatible with most automotive type thermistors with Borg
Warner, Delphi and Ford IAT sensors being pre-configured and selectable on a drop
down menu.
Other transducers not pre-set may have their profiles added and stored under user
selectable names for future use by HCT factory personnel.
If other thermistors are to be added, the acceptable Ohmic range is 50ohms at the
maximum temperature that can occur in the system to 2Mohm at the minimum
temperature that can occur in the system.
Open (> 2 M ohm) or shorted (< 50 ohms) thermistor inputs will be detected and
cause full fan speed output and indicate with the appropriate alarm response and
error code to aide diagnosis of the problem.
Each thermistor input can also be configured and used as simple contact closure
switch inputs.
Switch inputs to the controller MUST indicate HIGH temperature by disconnecting (
open circuit ) or tying the input(s) to the units power supply voltage and indicate LOW
temperature by grounding the input.
This switching convention is required to provide „Fail-safe‟ operation as the input(s) is
normally internally pulled to +5VDC with a current limiting resistor.
When a input(s) reads a HIGH temperature ( NOT grounded ), it produces a fixed error
value that is acted upon by the controller to determine the fan speed ( on or off ).
The controller operation is based on input from up to three temperature measured
zones.
One, two or all three inputs can be used depending on the system requirements with
all three thermistor inputs able to be enabled or disabled independently within the
set-up software.
The inputs can be from NTC ( Negative Temperature Coefficient ) Thermistors or Bi-
Metallic temperature switches and the choice can be made in the set-up software.
Thermistor Requirements :
Temperature ‘Switched’ Inputs
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