Service and troubleshooting
EST3 Installation and Service Manual 8.77
Wiring problems
There are three basic causes of wire-related erratic Addressable
Analog circuit operation:
Excessive wiring resistance
Rarely is excessive wiring resistance the sole cause of
Addressable Analog circuit problems. For any length of cable,
the amount of resistance and capacitance per foot doesn’t change
and the Addressable Analog circuit capacitance limits are usually
reached before the resistance limits. The digital signal operates
between 0 and 24 Vdc.
Excessive circuit resistance causes the
signal to shrink from a maximum of 23 Vdc to a lower voltage,
for example 20 Vdc. The 3-volt drop in the wiring is due to wire
resistance.
To measure Addressable Analog circuit voltage drop, use an
oscilloscope to measure the peak voltage at the Addressable
Analog module and at each analog addressable device.
If the
voltage difference is greater than 2 Vdc, the resistance in the
wire run is excessive. Too much resistance in the Addressable
Analog wire run is typically caused by small wire size or a bad
connection.
If the wire size is too small for the run length, the only remedies
are to replace the wire with a larger size, or install additional
Addressable Analog modules, dividing the circuit into acceptable
lengths.
Breaks or bad connections in the Addressable Analog
circuit wiring can be identified by comparing the calculated
circuit resistance value (described earlier) with the measured
circuit resistance value.
The measured wiring circuit resistance
should not be different from the calculated circuit resistance by
much more than a few ohms.
Excessive wiring capacitance
The second cause of erratic Addressable Analog circuit operation
is too much capacitance in the Addressable Analog circuit
wiring.
Capacitance distorts the digital signal. As wiring
capacitance increases, the square edges of the digital waveform
start to curve.
Excessive wiring capacitance causes the waveform
to curve beyond the point where a device can recognize the
waveform and respond when polled.
Wiring capacitance also effects the turn-on current spike. If the
turn on current spike is not present in the digital sequence, there
is a high probability the analog addressable device’s
communication will not be understood by the Addressable
Analog communication module.
To Next Page
Loading...