Seametrics AO45 - Manual (Page 2)

3. A non-isolated circuit is simpler because it only re-
quires one power supply. As a general rule, the stan-
dard SeaMetrics PC1 power supply can power both the
control and the 4-20 mA loop up to 300 Ohms imped-
ance.
The connection for AO45M meter mounted units as sup-
plied is non-isolated, with a jumper wire preinstalled to
power the 4-20 mA loop. If an isolated connection is
necessary, unscrew the cover and remove the circuit
board to expose terminals. Reconnect the unit follow-
ing the “Isolated power source” diagram.
For a wall mount unit, connect the flow sensor first. Then
connect the 4-20 mA output, following the appropriate
diagram. Finally, connect the power supply.
Mounting. Only the wall mount (W) housing style needs
to be mounted. The meter mount (M) unit comes
preinstalled on a flow meter or sensor. To mount the W
housing, remove the front cover. Locate the screw holes
underneath the four cover screw holes. Mark the cen-
ters and drive screws through these holes into a secure
surface. It is important to use only these holes, which
are isolated from the interior of the enclosure, in order to
keep the enclosure leaktight.
Connections. See the “Connections” diagrams on page
4. Determine whether or not the 4-20 mA output needs
to be isolated:
1. If the external 4-20 mA device has its own built-in
power supply, follow the “Isolated power source” dia-
gram.
2. Isolation prevents certain potential problems, such as
ground loops. It also allows a higher voltage to be used
for the 4-20 mA loop (up to 35 VDC) to drive a higher-
impedance load, roughly above 300 Ohms. Typically the
literature provided with the 4-20 mA device will specify
its impedance.
Installation
35
31
Loop
Power
(VDC)
27
24
21
18
15
12
50 200 650 1200
Load vs. Supply Voltage
Load Resistance
2 of 4
DIS
CON
TIN
UED