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SECTION 12 - CURRENT MODULE (CM-2)
The Multiplexer (MUX) is an electronic switch with 8
inputs and 1 output. The address applied to it determines
the position of the switch (i.e., which input is routed
to the output). The inputs to channel 0 through 6 are
grounded (0 VDC) . The input to channel 7 is a 0 to
4.0 VDC analog signal, representing motor current over
the range of 0 to 100% FLA. It is factory calibrated by
potentiometer R34 to be 4.0 VDC when the compressor
motor current is at 100% FLA. Under Program control,
the microboard commands the MUX to route the inputs
to the MUX output by applying 3-bit Binary addresses
to the MUX address inputs at J5-1,2,3. The voltage level
for a logic 1 is +12 VDC and logic 0 is 0 VDC. The mi-
croboard reads the MUX outputs at J5-6. It first address-
es channel 0 to determine the type of starter applied. The
0 VDC at channel 0 indicates to the microboard that this
is an Electromechanical Starter application. In all starter
applications, the microprocessor reads channel 0 to de-
termine the type starter applied:
• 0 VDC = EM starter
• More than 0 VDC=Solid State Starter
It then addresses channel 7 (ignoring channels 1
through 6) to read the analog motor current voltage.
The microboard interprets this analog value in terms of
% FLA and displays it upon operator keypad request.
It also uses this value to invoke compressor motor Cur-
rent Limit at 100% FLA and 104% FLA. When motor
current rises to 100% FLA, the microboard prevents
any further current rise by inhibiting further Pre-ro-
tation Vanes (PRV) opening until it decreases to 98%
FLA. If the motor current continues to rise to 104%
FLA, the microboard applies a close signal to the PRV
until the motor current decreases to 102% FLA. While
Current Limit is in effect, MOTOR - HIGH CUR-
RENT LIMIT is displayed.
130
As detailed in the SECTION 33 - SYSTEM CALIBRA-
TION, SERVICE SETPOINTS, AND RESET PROCE-
DURES of this manual, to field calibrate potentiometer
R8, the PRV must be manually operated to achieve
105% FLA compressor motor current. Therefore, dur-
ing this procedure, Current Limit is not invoked un-
til 107% FLA and 110% FLA. The first time the PRV
OPEN key is pressed on the COMPRESSOR Screen
after logging in at SERVICE access level, a 10 minute
window is opened, allowing the current to rise to 107%
FLA before further PRV opening is inhibited. This in-
hibit is released when the current decreases to 106%
FLA. If the current continues to rise to 110%, manual
control is overridden and a close signal is applied to the
PRV until the current decreases to 109% FLA. After 10
minutes, the normal current limit thresholds of 100%
FLA and 104% FLA are applied.
The MUX address inputs along with respective outputs
are as shown in the following table:
TABLE 10 - MUX ADDRESS
BINARY
J5-1
J5-2
0
0
0
0
1
1
1
1
JCI COMPANY CONFIDENTIAL
ISSUE DATE: 10/25/2019
DECIMAL
J5-3
0
0
0
0
1
1
1
0
2
1
1
3
0
0
4
0
1
5
1
0
6
0 to 5.0 VDC motor
current analog signal
1
1
7
calibrated on CM-2
board to be +4.0 VDC
at 100% FLA.
FORM 160.54-M1
OUTPUT
Ground
Ground
Ground
Ground
Ground
Ground
Ground
JOHNSON CONTROLS
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