97
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
6
SECTION 6 - I/O BOARD
I/O BOARD
The I/O (input/output) Board conditions the Digi-
tal inputs for the microboard and conditions the mi-
croboard’s Digital Outputs for application to other
components and devices. The left side of the I/O Board
performs the Digital inputs function; the right side per-
forms the Digital Outputs function. See
DIGITAL INPUTS
Digital inputs are ON/OFF inputs to the microboard
from relay and switch contacts, such as flow switches,
start/stop switch, and remote cycling/safety devices
(See
). The microprocessor
reads the state of these contacts and reacts per the
Program instructions. The contact voltage is 115 VAC
when closed and 0 VAC when open. These voltages are
not suitable for direct input to the microboard. There-
fore, the I/O Board converts the 115 VAC / 0 VAC con-
tact voltages to 0 VDC/+5 VDC logic level inputs for
the microboard. Individual Optocoupler circuits (See
each Digital Input. When the input is 115 VAC, the out-
put will be 0 VDC; when the input is 0 VAC, the output
will be +5 VDC.
Field connected Digital inputs, such as those from
external devices that cycle the chiller, are connected
to terminal strip TB4 (See
).
These inputs are in the form of dry contacts connected
as shown in
. The 115 VAC
power source that is switched by the remote contacts
is supplied by the I/O Board TB4-1. There are mul-
tiple TB4-1 terminals located adjacent to the field input
connections, as shown in
DIGITAL OUTPUTS
Digital Outputs are ON/OFF outputs from the mi-
croboard that control solenoid valves, motor contactors,
actuators, system relays and provide operating status
to external devices (See
Program instructions. The microboard energizes and
de-energizes these devices.
The coils of these devices operate on 115 VAC and
therefore cannot be directly connected to the mi-
croboard. The Digital Outputs section of the I/O Board
co12 VDC coil relays that are driven by the
microboard’s logic level outputs. The contacts of these
+12 VDC relays operate the external 115 VAC coil de-
vices. On the I/O Board, one side of the each of the
relay coils is permanently connected to +12 VDC at
J19-26/27. The other side of each relay coil is con-
nected to the microboard via I/O Board connector
J19. The microboard energizes each relay by driving
the appropriate input at J19 to logic low voltage level
(ground potential). The DC voltage at the appropriate
input pin at J19 will be a logic high (greater than +10
VDC) when the microboard is commanding a relay to
de-energize; logic low (less than +1 VDC) when com-
manding a relay to energize.
Relay K18 is different from all other relays on the I/O
Board; it has a 115 VAC coil. It provides the start/stop
signal to the Compressor Motor Starter and provides
Compressor Run
status to remote devices (See
). Relay K18 is controlled by DC re-
lays K13 (start) and K14 (stop). To start the compressor
motor, the microboard energizes K13 and K14 simulta-
neously. The 115 VAC at TB1-6 is applied to the coil of
K18 via K13 contacts, energizing K18. Approximately
0.2 seconds later, K13 is de-energized. K18 remains
energized through K14 contacts and holding contacts
of K18. To stop the compressor motor, the microboard
de-energizes K14. To prevent sags in Utility Power
from chattering K18, the holding contact of K18, along
with the contact of K13, creates an anti-chatter circuit
for relay K18. Once energized, K18 cannot be re-ener-
gized until K13 is again energized; this will not occur
until after a controlled shutdown has occurred and an-
other start sequence has been initiated.
There are conditions external to the I/O Board required
to energize relay K18. The 115 VAC will be present at
TB1-16 only if the motor controller contacts CM are
closed and the circuit between external Terminal Strip
TB6-1 and TB6-53 is closed. The CM are located on
the CM-2 Board (relay K1), Electromechanical Starter
applications, the Solid State Starter Logic Board (relay
K1), Solid State Starter applications or a relay mounted
on the Variable Speed Drive Logic Board on Variable
Speed Drive applications. The High Pressure safety
switch “HP”, must be closed and the
RUN
Switch
“1SS” must be in the
Run
position.