Siemens DataNET Hub (DNH) - Manual (Page 46)

38 •••• Installation 2000585-001
Signal Equalizer Settings for Non Recommended Cable or Unknown
Cable Lengths,
Continued
Signals are viewed with an oscilloscope.
Scope characteristics: 10 MHz bandwidth capable of measurement sen-
sitivity of 0.2 v/div to 1.0 V/div. A typical two-channel scope can be em-
ployed using the channel 1 - channel 2 capability. Use X10 probes to
reduce the loading of signals.
Connect the two scope probes to the positive and negative terminals of
the HUB Communications board, not the Equalizer board, of the channel
to be measured. Alternatively, a connection can be made to the leads of
the fuses for the selected channel.
• Set time base to ~1 or 2 millisecond per division.
• Observe two sequential signal envelopes of 3-4 millisecond length.
The first signal envelope is the poll from the HUB to the slave device,
and the second is the response back from the slave device. The reading
from the poll should be ~5 volts p-p. The response may be from ~5 volts
p-p (for a short cable with 150 ohm setting) to ~0.75 or 0.8 volts p-p (for
a maximum cable length). Responses from a short cable with 100 ohm
impedance settings are ~4 volts p-p.
If a large amount of common mode line frequency interference is present
the above choice may be unsuitable. In this case, Option 2. is recom-
mended.
This option observes the signal across the termination resistor for the
selected port.
Using this option, connect the two scope probes across an unused im-
pedance jumper location. For instance, if the jumper is in the 120-ohm
location, connect the probes on the two pins for the 100-ohm jumper po-
sition. A short adapter cable with a two-positioned socket on one end
simplifies this connection.
Both channels should be ac-coupled to avoid interference from the 2.5
Volts dc common mode level.
Using this method there is only one reading, the response message,
which is seen. Responses may be from ~5 volts p-p (for a short cable
with 150 ohm setting) to ~0.75 or 0.8 volts p-p (for maximum cable
length). Responses from a short cable with 100 ohm impedance settings
are ~4 volts p-p.
View Measurements
Option 1.
Connection Point
Option 2. Connection
Point