28 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
3.
Check the voltage and polarity of the N2 DC bias voltages at the
ASC. Do so by connecting the DMM across N2+ and REF
(Figure 14). Write down the reading. Repeat for N2– and REF, then
for N2+ and N2–. Compare the voltages you read to the following
values:
N2+ to REF = +2.45 to 2.98 VDC
N2– to REF = +2.06 to 2.54 VDC
N2+ to N2– = +0.36 to 0.92 VDC
If your readings are not (approximately) at these values, that
particular wire is grounded, shorted, or crossed with another wire.
Correct and measure again.
If your readings are within these values, the bus is properly wired.
You can use an oscilloscope to pinpoint communication faults over the
N2 Bus. The procedure requires a 2-channel scope with an A minus B
function or an A plus B with B inverted function. Follow these steps:
1.
Plug the scope into a grounded electrical outlet.
2.
Set both channels to 2 volts per division. Both channels must have
the same gain or volts per division setting.
3.
With no signal applied, adjust each channel’s vertical position at the
same graticule on the screen (i.e., center screen).
4.
Select the channel A minus B function. If your scope does not have
this function, select the Add function (channel A ADDED to B then
INVERT channel B).
5.
Select the 0.5 mS horizontal range.
0 V -
Ch 1 = 2 V/div.
T/div .5 mS
3 to 10 V pp
(inc0.5 VDC bias)
SCOPESG
Figure 15: N2 Bus Signal as Measured with Oscilloscope
TEST 4:
Oscilloscope
Summary of Contents for METASYS ASC
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