Johnson Controls METASYS ASC, Networking And Troubleshooting Manual

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22 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
VOLTAGE2
N2+ to REF
+2.45 to 2.98 VDC
N2+ to N2-
+0.36 to 0.92 VDC
N2- to REF
+2.06 to 2.54 VDC
N2 Bus Terminal Block
N2 -
N2 +
REF
For best reading, place probe on metal
plate inside terminal, not on screw. Note:
N2 -
UNT / VAV
AHU / LCP
ZBus
REF
N2 +
DMM DMM
Figure 11: Measuring N2 Voltages at ASC
4. Before connecting the three N2 Bus wires, identify the correct voltage
and polarity of each wire with the DMM. The voltages should match
the following:
N2+ to REF = +2.45 to 2.98 VDC, referenced to REF
N2– to REF = +2.06 to 2.54 VDC, referenced to REF
REF =
≤
1.0 VDC/VAC, referenced to earth ground with 100K ohm
resistor
If the voltages are not within the above ranges, end-of-line termination
may not be set correctly. Locate and fix the problem.
5. Connect the N2 Bus wires to the ASC and continue to the next ASC.
Perform Steps 3 and 4 until you have connected each ASC to the
N2 Bus.
These five steps comprise the simplest but most thorough N2 Bus test.