Emerson Autochangeover Controllers AC8 - Manual (Page 25)

Wiring and Connections
17
3.3 Connecting Analog Inputs
The analog input connector blocks are at the bottom center of the AC8 printed circuit board, as shown
below right. The blocks are two-part assemblies to permit easier connections. To determine the proper
wire size, see Table 4 - Wiring specifications.
To connect an input:
1. Turn OFF electrical power to the AC8.
2. If necessary, remove a conduit knockout to permit wire entry into the AC8 enclosure.
3. Bring the wire(s) into the AC8 enclosure through a
conduit knockout or access slot.
4. Loosen the appropriate screw and slip the stripped
end of the wire into the terminal block.
5. Tighten the screw until it holds the wire snugly.
3.3.1 Setting the 12VDC/24VDC Analog Power Jumper
The analog power jumper sets the common voltage
that is applied to all of the analog input connections.
The jumper permits the user to modify the voltage
supplied to the sensors, according to the power
requirements.
The factory default position is 24VDC; it may be
changed to 12VDC.
To change the analog power jumper setting:
1. Find the black analog jumper on the circuit board,
as shown at right. The jumper is at the bottom of
the board near the middle (see 1.7 - Controller
Board Overview).
2. Decide whether your configuration requires the jumper to be 24VDC or 12VDC.
3. Set the jumper as needed:
• To set the jumper to the 24VDC position, place the black jumper on the middle and right pins.
• To set the jumper to the 12VDC position, place the black jumper on the middle and left pins.
3.3.2 Connecting the Analog Ground
The AC8 features an analog ground connection
for four-wire sensors that have an external
power source. Such a four-wire sensor requires
a reference to ground because they get power
from an external power source.
A two-wire transducer, which does not have an
external power source, does not need to be
connected to the analog ground.
The analog ground connector has two
terminals, each of which can accommodate two
wires. This is adequate to connect four sensors
that require a reference to ground because they
get power from an external power source.
Connect the analog ground to an external
four-wire sensor, as shown in the illustration at
right.
485
+ —
+ — OM)
S
422 TB9: ANALOG
GROUND
AG
+ + — —
+ — + —
3-4 BOTTOM
1-2 TOP
Analog
inputs
Analog
ground
Analog
power
jumper
+
+
+
—
—
+
(TOP)
(BOTTOM)
TB10: COMMS
4/20mA
Output
24V Input
TB9: ANALOG
GROUND
3-4 BOTTOM
1-2 TOP
Analog
ground
Analog
input
Four-wire
transducer
Sensor
with
external
power
24V from
external
power
source