Section 5 - I/O Board; I/O Board; Digital Inputs; Digital Outputs - Johnson Controls YORK OPTIVIEW YK Series Service Instructions Manual

FORM 160.54-M1

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. Refer to Figure 25
on Page 75.

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
(Refer to Figure 26 on Page 76). The microproces-
sor reads the state of these contacts and reacts per the
Program instructions. The contact voltage is 115VAC
when closed and 0VAC when open. These voltages are
not suitable for direct input to the microboard. There-
fore, the I/O Board converts the 115VAC/0VAC con-
tact voltages to 0VDC/+5VDC logic level inputs for
the microboard. Individual Opto-coupler circuits (Re-
fer to Figure 27 on Page 77) perform the conversion
for each Digital Input. When the input is 115VAC, the
output will be 0VDC; when the input is 0VAC, the out-
put will be +5VDC.
Field connected Digital inputs, such as those from ex-
ternal devices that cycle the chiller, are connected to
terminal strip TB4 (Refer to Figure 26 on Page 76).
These inputs are in the form of dry contacts connected
as shown in Figure 28 on Page 77. The 115VAC
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 Figure 25 on Page 75 and
Figure 26 on Page 76.

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 (Refer to Figure 29 on Page 78).
Per Program instructions. The microboard energizes
and de-energizes these devices.
The coils of these devices operate on 115VAC and
therefore cannot be directly connected to the mi-
JOHNSON CONTROLS

SECTION 5 - I/O BOARD

croboard. The Digital Outputs section of the I/O Board
contains +12VDC coil relays that are driven by the mi-
croboard's logic level outputs. The contacts of these
+12VDC relays operate the external 115VAC coil de-
vices. On the I/O Board, one side of the each of the re-
lay coils is permanently connected to +12VDC at J19-
26/27. The other side of each relay coil is connected to
the microboard via I/O Board connector J19. The mi-
croboard energizes each relay by driving the appropri-
ate input at J19 to logic low voltage level (ground po-
tential). The DC voltage at the appropriate input pin at
J19 will be a logic high (greater than +10VDC) when
the microboard is commanding a relay to de-energize;
logic low (less than +1VDC) when commanding a re-
lay to energize.
Relay K18 is different from all other relays on the I/O
Board; it has a 115VAC coil. It provides the start/stop
signal to the Compressor Motor Starter and provides
Compressor Run status to remote devices (Refer to
Figure 29 on Page 78). Relay K18 is controlled
by DC relays K13 (start) and K14 (stop). To start the
compressor motor, the microboard energizes K13 and
K14 simultaneously. The 115VAC 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 mo-
tor, the microboard de-energizes K14. To prevent sags
in Utility Power from chattering K18, the holding con-
tact of K18, along with the contact of K13, creates an
anti-chatter circuit for relay K18. Once energized, K18
cannot be re-energized until K13 is again energized;
this will not occur until after a controlled shutdown has
occurred and another start sequence has been initiated.
There are conditions external to the I/O Board required
to energize relay K18. The 115VAC 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), Electro-Mechanical Start-
er 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 Pres-
sure safety switch "HP", must be closed and the RUN
Switch "1SS" must be in the Run position.
5
71