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SECTION 4 - MICROBOARD 031-02430-000 AND 031-02430-001
Style "F" (and later) chillers are supplied with factory-
mounted Flow Sensors on the evaporator and condenser.
These are electronic thermal-type sensors. The operat-
ing principle of the sensor is thermal conductivity. It
uses the cooling effect of a flowing liquid to sense flow.
The temperature of the heated sensor tip is sensed by a
thermistor located in the tip. A second thermistor, located
higher in the tip in a non-heated area, is only affected by
changes in liquid temperature. The temperatures sensed
by the thermistors are compared. Flowing liquid car-
ries heat away from the heated sensor tip, lowering its
temperature. The higher the flow rate, the lower the tip
temperature and therefore a lower differential between
thermistors. Lower flow rates remove less heat from
the tip allowing a higher tip temperature. The lower the
flow, the greater the differential between thermistors.
The sensor is vendor-calibrated to turn ON its output at
a flow rate of 20cm (0.6 ft.)/second. This is the setpoint.
There are 11 LED's on the sensor that reflect the mea-
sured flow rate. The center located amber LED illumi-
nates at the setpoint flow rate (and above). The 4 LED's
to the left of the amber reflect flow rates below the
setpoint. The 6 LED's to the right of the amber reflect
flow rates above the setpoint. As the flow rate decreases
from the setpoint, the LED display moves to the left.
As the flow rate increases above the setpoint, the LED
display moves to the right.
The sensor operates from a 24 VAC power source and
has a solid state relay output. On each sensor, one side
of the solid state relay (pin 4) is connected to +5 VDC
on the microboard and the other side (pin 2) is connected
to an Analog Input of the microboard (See Figure 77 on
page 175 and Figure 24 on page 72). After power is
applied, there is a thermal warm-up period of up to 20
seconds. During this time, the output could be unstable.
When the setpoint (or greater) flow rate is sensed, the
solid state relay output is turned ON causing it to con-
duct current through the 7.5K ohm Microboard load re-
sistor to the +5 VDC. This applies greater than +4 VDC
to the microboard input. When a flow rate less than the
setpoint is sensed, the solid state relay output is turned
OFF, resulting in no conduction through the load resis-
tor. This applies less than 1 VDC to the microboard in-
put. To determine the state of the solid state relay, first
confirm that +5 VDC is present at pin 2 of the flow sen-
sor. Then connect a voltmeter between the microboard
TP1 (GND) and the respective flow sensor input to the
microboard.
56
The software accommodates either the Paddle type
sensors connected to the TB4 of the I/O Board or the
Thermal type sensors connected to either J7 or J14 on
the microboard. The actual connection point of the
Thermal type sensors to the microboard is determined
by the chiller vintage (See Figure 77 on page 175 and
Figure 24 on page 72). On new production chillers
before June 2009, they are provided connected to the
microboard J7. On new production chillers after June
2009, they are provided connected to the microboard
J14. To ensure that the program reads the correct input,
the Flow Switch setpoint on the OPERATIONS Screen
must be set appropriately as explained in SECTION 33
- SYSTEM CALIBRATION, SERVICE SETPOINTS,
AND RESET PROCEDURES .
Serial Data Ports
Microboard 031-02430-000 is equipped with 6 serial
data ports. Microboard 031-02430-001 is equipped
with 7 serial ports. See Figure 21 on page 69. Each
port is dedicated for a specific function as follows:
A. COM1 (J2) – RS-232. Printer.
B. COM2 (J13) – RS-232 on Microboard 031-02430-
000. RS-232 or RS-485, as selected with Program
Jumper JP17 on Microboard 031-02430-001. The
RS-485 port is used for Modbus communications
to the Liquid Cooled Solid State Starter, Medium
Voltage Solid State Starter, Medium Voltage Vari-
able Speed Drive and Variable Speed Drives. The
RS-232 port is not used.
C. COM3 (J12) – RS-485. Hot gas bypass, Heat Re-
covery, Head Pressure Control, Motor Monitor-
ing.
D. COM4 (4A-J11), (4B-J2) – This port is actually
two ports. However, they cannot be used simul-
taneously. The position of program jumper JP27
determines which port can be used. COM4A
– RS485 not used. COM4B – RS-232 E-Link
Gateway.
E. COM5 (J15) – Opto-coupled transmit/receive.
VSD Adaptive Capacity Control Board or Style B
Solid State Starter.
Each port is equipped with two LED's. A red TX LED
illuminates as data is transmitted to or requested from
another device. A green RX LED illuminates as data
is received from another device. The RS-232 voltages
are industry standard +5 to +25 VDC and -5 VDC to
-25 VDC logic levels. The RS-485 voltages are indus-
JCI COMPANY CONFIDENTIAL
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
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