Page 26 IM 781-2
4. Outdoor Air Temperature Sensor (UI 5)
The outdoor air temperature sensor may be used to reset the System Setpoint, cooling tower bypass valve control, optimal
start, and/or low ambient lockout.
Note: Outside Air Temperature may also be supplied by a BAS or from a chiller (if one of the chillers in the system
provides OAT.)
5. Decoupler Temperature Sensor (UI 6)
The decoupler temperature sensor is used when decoupled chiller sequencing control is required (for primary/secondary
piping configurations). See Figure 7 through Figure 10 for the location of the decoupler line temperature sensor.
The decoupled chiller sequencing control will increase the system capacity when the decoupler line temperature is greater
than the common chilled water supply temperature by more than an adjustable differential. This feature provides extra
primary water flow to match the secondary water flow (even though more cooling capacity is not required).
0-10 VDC Inputs or 4-20 mA Inputs
CSM onboard universal inputs 7 to 12 are set to receive 10-VDC signals. These inputs support self-powered 0-10 VDC
sensors. Input impedance is greater than 5K ohms. Accuracy is ±2% of span, without user calibration. The onboard I/O’s
analog inputs are isolated from ground as long as the 24-volt power supply does not have its common tied to ground. Do
not wire the secondary side of this 24-volt transformer to ground. The analog input common terminals are tied to each
other. Ground loops could occur through the onboard I/O if it is connected to two or more external devices that are not
isolated from ground.
!
CAUTION
Ground loop current hazard.
Can cause equipment damage.
If analog inputs on a MicroTech II CSM onboard I/O are connected to more than one external device, the
connected analog outputs of those devices must be isolated from ground. If they are not, ground loop currents
could occur which could damage the MicroTech II and connected equipment. If external devices do not have
their analog outputs isolated from ground, condition the signal with a signal isolator on each device.
Figure 21. Analog Input 0-10VDC Wiring
UI1
G
UI2
Shield
Stud in
enclosur
200' max
Shielded,
Cable
Range: 0-10 Vdc
Input Impedance > 5K ohms
0-10 Vdc
0-10
Vdc
+
-
CSM onboard universal inputs 7 to 12 can also receive 4 to 20 mA signals with the addition of a 499-ohm resistor (see
Figure 22). Resistors are provided with the CSM. These inputs support self-powered or controller-powered sensors.
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