Frequently Asked Question

485 Network Problem - End of line termination resistor
Last Updated 10 years ago

If you encounter network problems, then the use of a 120 Ohm resistor, with a tolerance of +/- 1%, may be used as an end of line termination resistor.

This should be fitted across the A (+) & B (-)network cables at the start and end of the network cable.

Note : Depending on the network wiring the Data Manager may not be the first/last device in the network. If it is in the middle you would have to find the network cable start/finish and fit the termination resistor at the devices at the end of the cable.

You should always use the correct network cable for RS485 networks (i.e Belden 8723). This has x2 twisted pairs, coloured red & black and green & white. The signal used is a differential. This means the twisted pairs are used for noise cancellation purposes.
Therefore if the networked devices and cable are fitted in an electrically noisy environment the correct cables must be used for the A(+) and B (-) signals i.e. Red & Black or Green and White. You could not use Red and White etc.

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