Hardwired Chiller Remote I/O Module Analog Inputs; Chiller % Rla (Ai 1); Chillers With % Rla Output; Figure 31. Direct % Rla Signal From Chiller - McQuay MicroTech II Installation Manual

Hardwired Chiller Remote I/O Module Analog Inputs

Chiller % RLA (AI 1)

The CSM displays the chiller's % RLA and uses it on a hardwired chiller when deciding when to perform a stage-up or a
stage-down. The CSM also uses % RLA on a hardwired chiller to determine when that chiller is in the "running" state.

Chillers With % RLA Output

If the chiller supplies a % RLA output, wire that output directly to AI 1 on the hardwire remote I/O module. Set the %
RLA Input Type property to % RLA from chiller (4-20 mA) or % RLA from chiller (0-10 VDC). If the signal is 4-20 mA,
install a 499 ohm resister across AI 1.

Figure 31. Direct % RLA Signal from Chiller

Special Considerations when using % RLA Signal from a McQuay MicroTech Series 200 Centrifugal Chiller
McQuay MicroTech Series 200 Centrifugal chillers offer an optional analog output representing compressor % RLA. If
you are using this output, follow these guidelines:
1. Use the 0-10 VDC output option. The AOX-4 auxiliary board can be configured for 0-10VDC, 0-5 VDC, 0-20 mA, or
0-5 mA outputs. Use the 0-10 VDC option when connecting it to the hardwired chiller remote I/O module. The 4-20
mA option, when the board is powered with 12 VDC, cannot drive enough current through the 499 ohm resistor
required across the module's analog input. Set the % RLA Input Type property for this chiller = "% RLA from chiller
(0-10 VDC)".
2. On a MicroTech Series 200 Centrifugal chiller, the 0-10 VDC output represents a % RLA range from 0% to 125%.
This means that the compressor is running at 100% when the compressor % RLA output reads 8 VDC across the
analog input of the remote I/O module. Set the RLA Signal At 100% property for this chiller = "8 VDC".
3. If the MicroTech Series 200 Centrifugal chiller is a dual compressor unit, both % RLA outputs (one from each
compressor) must be averaged with an external device. This average value is then entered into the hardwired chiller
remote I/O modules AI 1. Table 8 lists the specifications of a universal math device that can be used to average both
signals. Since the dual compressor chiller typically does not already have the optional analog outputs boards providing
4-20 mA output of % RLA, you may instead choose to use a single current transducer on the entire chiller.
IM 781-2
499 Ω Resistor (not required if
chiller output is ...10 VDC)
11-(Y)
AI #1
10-(0)
Hardwired Chiller's
Remote I/O Module
+
%RLA Analog
-
Output
Chiller Unit Controller
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