36
FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 3 - MICROBOARD 031-01730-000
JCI COMPANY CONFIDENTIAL
JOHNSON CONTROLS
Style F (and later) chillers are supplied with factory-
mounted flow sensors on the evaporator and condenser
(Software version C.MLM.01.07.xxx (and later) is re-
quired for this feature. These are electronic thermal-
type sensors. The operating 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 thermis-
tors are compared. Flowing liquid carries 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 allow-
ing 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 measured flow rate. The center located amber LED
illuminates at the setpoint flow rate (and above). The
4 LED’s to the left of the amber reflect flow rates be-
low 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 output (pin 2) is connected to the
micr5 VDC and the other side (pin 4) is con-
nected to a Microboard Analog Input (See
).
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 conduct current through the 7.5K ohm Microboard load
resistor to the +5 VDC. This applies more than +4 VDC
to the microboard input evaporator J7-14; condenser J7-
16). When a flow rate less than the setpoint is sensed, the
solid state relay output is turned OFF, resulting in no con-
duction through the load resistor. This applies less than 1
VDC to the microboard input. To determine the state of
the solid state relay, first confirm that +5 VDC is present
at pin 2 of the flow sensor. Then connect a voltmeter from
Microboard J7-14 (evaporator) or J7-16 (condenser) to
Microboard TP1(ground).
Software version C.MLM.01.08.xxx (and later) allows
either the Thermal-Type sensors connected to the mi-
croboard Analog Inputs or the Paddle-Type sensor con-
nected to the I/O Board Digital inputs. (See the Flow
TION, SERVICE SETPOINTS, AND RESET PROCE-
). To ensure that the program reads the correct
input for the flow sensor type present, the Chiller Style/
Compressor setpoint and Flow Switch setpoint must be
set appropriately.
Serial Data Ports
The microboard is equipped with 5 serial data ports
(See
). Each port is dedicated
for a specific function as follows:
A. COM1 (J2) – RS-232. Printer.
B. COM2 (J13) – RS-232. Not used.
C. COM3 (J12) – RS-485. Optional I/O.
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 st5 VDC to +25 VDC and -5 VDC to
-25 VDC logic levels. The RS-485 voltages are indus-
try standard 0 VDC and +1.5 VDC to +5 VDC logic
levels. COM5 logic levels are 0 VDC and +5 VDC. A
diagnostic test can be performed on each serial port to
confirm proper operation. See Diagnostics
34 - DIAGNOSTICS AND TROUBLESHOOTING
of
this manual.
The LEDs and their functions are as follows:
• CR2 RX1 – COM1 serial port receive data.
• CR3 TX1 – COM1 serial port transmit data.
• CR12 TX4 – COM4 serial port transmit data.
• CR13 RX4 – COM4 serial port receive data.
• CR15 TX3 – COM3 serial port transmit data.
• CR14 RX3 – COM3 serial port receive data.
