External Chilled Water Setpoint (Cws); Resistor And Potentiometer - Trane RTAA-70 Installation & Maintenance Manual

RTAA-SVX01A-EN
Installation — Electrical
reentered until the unit has been switched out of ice-building mode (open
5K20 contacts) and then switched back into ice building mode (close 5K20
contacts).
In ice-building, the current setpoint will be set at 120%. For example, if the
Front Panel or External Current Limit setpoint is set to 80%, in ice-building
the Active Current Limit is 120%.
If, while in ice-building mode, the unit gets down to the freezestat setting
(water or refrigerant), the unit will shut down on a manually resettable
diagnostic, just as in normal operation.
Connect leads 501 and 502 from 5K20 to the proper terminals 1U2TB1 -1 and
-2. Refer to the field diagrams which are shipped with the unit.
Silver or gold-plated contacts are recommended. These customer furnished
contacts must be compatible with 12 VDC, 45 mA resistive load.

External Chilled Water Setpoint (CWS)

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.
To enable external setpoint operation, "External Chilled Water Setpoint
"(Operator Settings Menu) should be set to "E" using the Clear Language
Display.
Figure 27

Resistor and Potentiometer

Arrangement External Chilled Water Setpoint
1. Remote Resistor/Potentiometer Input (fixed or adjustable).
Connect the remote resistor and/or potentiometer to terminals 1TB1-3 and
TB1-5 of Options Module 1U2, as shown in
For units with 40 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 (±10%) and a fixed 15 Kohm (±10%) 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 Clear Language
Display showing "Active Chilled Water Setpoint" (Chiller Report Menu), the
Clear Language Display can be used to calibrate the positions of the potenti-
ometer to correspond with the desired settings for the leaving water temper-
ature. External resistor input values for various chilled water setpoints are
shown in Table 14.
Figure 27.
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