10 — Troubleshooting
Notes
Rev 3-97
@ Crown
Figure 7 shows what a wave form may look like when the loop capacitance is
too high. Note that the waves are rounded and unable to reach magnitudes
required for reliable communication. In high capacitance situations the prob-
lem may result in loss of high current or low current values. When the problem
is extremely high RFI the problem is more likely to be a loss of low current values.
OUT
IN
+ – + –
SMX 1
OUT
IN
+ – + –
SMX 2
OUT
IN
+ – + –
SMX 3
OUT
IN
+ – + –
SMX 4
100
Ω
+
–
SCOPE
4 ma
Low
Current
12 ma
High
Current
Ideal Crown Bus Waveform Shape
High Capacitance Crown Bus Waveform Shape
4 ma
Low
Current
12 ma
High
Current
Figure 5. Loop Current Test
Figure 6. Ideal Loop Signal
Figure 7. Loop Signal With High Capacitance
