IM 781-2 Page 25
c) UI 13 through 16 = Digital Inputs. Dry contacts, 20 Hz. max. frequency. 3V open circuit, 300-uA short-circuit
current.
Temperature Inputs
CSM onboard universal inputs 1 to 6 are set to receive temperature data from Type 3 (10K) thermistors with a range of –10
to 135 °F (-23.3 to 57.2 °C). Input accuracy is in the range of ±1% of span.
Figure 20. Thermistor wiring
UI1
G
UI2
Shield
Stud in
enclosure
200' max
Shielded, Twisted
Cable
Range: -10—135
°F
10K (Type 3)
Thermistor
1. Chilled Water Supply Temperature Sensor (UI 1)
The common chilled water supply temperature sensor is always required. See Figure 2 for the location of the chilled water
supply temperature sensor.
When using standard chiller sequencing control, the common chilled water supply temperature sensor is used by the CSM
to determine when a system capacity increase is needed. The increase is determined when the leaving chilled water
temperature is greater than the common chilled water supply temperature by more than an adjustable differential.
When using decoupled chiller sequencing control, the common chilled water supply temperature sensor is also used by the
CSM to determine when a system capacity increase is needed to provide additional primary water flow. The increase is
determined when the decoupler line temperature is greater than the common chilled water supply temperature by more than
an adjustable differential.
When using common leaving chiller water temperature control, the common chilled water supply temperature sensor is
used by the CSM to set the Chiller Setpoint.
2. Chilled Water Return Temperature Sensor (UI 2)
The common chilled water return temperature sensor is used when return chilled water temperature reset, constant return
chilled water temperature reset, or optimal start is required. See Figure 2 for the location of the chilled water return
temperature sensor.
When using return chilled water temperature reset, the common chilled water return temperature determines the System
Setpoint.
When using the constant return chilled water temperature reset, the System Setpoint is reset by a constant return,
proportional/integral control loop function to maintain the common chilled water return temperature.
3. Condenser Water Temperature Sensors (UI 3 and 4)
The condenser water temperature sensors are used for cooling tower staging control and cooling tower bypass valve
control. Cooling tower control requires either a leaving condenser water temperature sensor or an entering condenser water
temperature sensor to be used as the control temperature. When cooling tower stage control is required, the first tower stage
is turned on when the control temperature exceeds the Stage 1 Setpoint.
When cooling tower bypass valve control (optional) is used, the CSM will maintain the control temperature at the Valve
Setpoint or Stage Setpoint.
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