72
RTAA-IOM-3
External Chilled Water
Setpoint (CWS):
Remote Resistor/Potentiometer,
Voltage Source 2-10 VDC, or
Current Source 4-20 mA
This option allows the external setting
of the Chilled Water Setpoint,
independent of the Front Panel Chilled
Water Setpoint, by one of three means:
1. A remote resistor/potentiometer
input (fixed or adjustable)
2. An isolated voltage input 2-10 VDC
3. An isolated current loop input
4-20 mA
Methods 2 and 3 are usually used in
interfacing with a Generic BAS or a
process controller to the chiller.
To enable external setpoint operation,
Item 30 of Menu 3, “External Chilled
Water Setpoint d/E”, should be set to
“E” using the Front Panel Operator
Interface.
1. Remote Resistor/Potentiometer Input
(fixed or adjustable)
Connect the remote resistor and/or
potentiometer to terminals TB1 -3
and TB1 -5 of Options Module 1U2,
as shown in Figure 38.
For units with 40 F to 60 F LCWS
range, a field-furnished 25 Kohm
linear taper potentiometer (±10%)
and a fixed 5.6 Kohm (±10%) 1/4 watt
resistor should be used.
For units with 20 F to 39 F LCWS
range, a field-furnished 25 Kohm
linear taper potentiometer (±1 0%)
and a fixed 15 Kohm (±1 0%) 1/4 watt
resistor should be used.
If the potentiometer is to be remotely
mounted, it and the resistor must be
connected to the UCM prior to
mounting. Then, with the UCM
display in Menu 0 and the display
advanced to “Active Chilled Water
Setpoint”, the UCM can be used to
calibrate the positions of the
potentiometer to correspond with
the desired settings for the leaving
water temperature. External resistor
input values for various chilled water
setpoints are shown in Table 13.
Table 13
Input Values Vs. External Chilled Water Setpoint
Inputs
Resulting Chilled
Resistance (Ohms) Current (mA) Voltage (Vdc) Water Setpoint (F)
94433 4.0 2.0 0.0
68609 5.2 2.6 5.0
52946 6.5 3.2 10.0
42434 7.7 3.9 15.0
34889 8.9 4.5 20.0
29212 10.2 5.1 25.0
24785 11.4 5.7 30.0
21236 12.6 6.3 35.0
18327 13.8 6.9 40.0
15900 15.1 7.6 45.0
13844 16.3 8.2 50.0
12080 17.5 8.8 55.0
10549 18.8 9.4 60.0
9050 20.0 10.0 65.0
Figure 38
Resistor and Potentiometer
Arrangement for External Chilled
Water Setpoint
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