6 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
This section describes how to install ASCs. The ASCs include the Air
Handling Unit (AHU) Controller, Lab and Central Plant (LCP) Controller,
Unitary (UNT) Controller, and Variable Air Volume (VAV) Controller.
Notes: These procedures are not required; however, they are
recommended to reduce installation errors.
If you are fairly confident that the field wiring has no earth
grounds, you may skip Step 2, which instructs you to measure each
field wire terminated to the ASC. Skipping this step shortens the
procedure. If you skip Step 2 and a field device is earth grounded,
it will be caught in Step 5 when the entire ASC is tested.
1.
Mount the ASC in an appropriate location as described in its technical
bulletin.
2.
Before terminating the field wires to the ASC, measure the resistance
of each wire to earth ground using an LED test circuit (preferred) or a
DMM. For the LED test circuit, assemble the test circuit shown in
Figure 2. Then, connect the circuit from each input to earth ground
and then to each output to ground. For the DMM test, connect the
DMM from each input to earth ground and then to each output to
ground (Figure 2).
If the LED turns On (or you read a value less than 1 Megohm at any
input or output), the circuit is improperly isolated. Replace or repair
the wiring or the field device; or, for a binary output, add an isolation
relay. Repeat the DMM test.
If the LED does not turn On (or you read a value greater than
1 Megohm), the circuit may be properly isolated. (It will not be
isolated if there are earth grounds that exist at higher voltages.)
A value of infinite ohms indicates a completely isolated circuit at
approximately zero volts. Connect this wire to the appropriate ASC
terminal and check the next wire.
Figure 2: Testing for an Isolated Circuit
ASC Installation
Steps
Field Device
IN/OUT
IN/OUT COM
DMM
ISOCIRCT
470 ohm
1/4-watt
9 V
Battery
(+)
(-)
Red LED
(15/20 mA)
LED Test Circuit (Preferred Method)
or
Summary of Contents for METASYS ASC
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