Siemens DataNET Hub (DNH) user manual View Measurements

Signal Equalizer Settings for Non Recommended Cable or Unknown Cable Lengths, Continued

View Measurements

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.

Option 1. Connection Point

Option 2. Connection Point

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.

38 • Installation 2000585-001