Detcon 1640-N4X - Manual (Page 23)

1640-N4X
1640-N4X Instruction Manual Rev. 0.0 Page 19 of 28
Measuring at the master device between dc common and A, or dc common and B should give a reading of
around 2.5vdc. Remember this is with the power on, but with no communication taking place.
Another method of troubleshooting is to enable the communications and remove all the slaves. Proceed to
plug 1 slave in and see if communication is good. If so, plug in the next slave and check again.
Repeat this with each slave until all of the slaves are plugged in or one of the slaves takes the data bus down.
The following table consists of recommended cables and their specifications from Belden. These cables are
designed with RS-485 in mind and should be used for RS-485 data buses.
Belden# pairs AWG Impedance
9841 1 24 120ohm
9842 2 24 120ohm
8132 2 28 120ohm
The root cause of many RS-485 communication problems can be traced back to incorrect cabling, incorrect
cable and wire types, and the use of incorrect wiring schemes. It is easier to avoid these problems by
following a few simple guidelines:
9 Use good wiring schemes (refer to Appendix A).
9 Use recommended cables.
9 Properly connect data lines and shields.
9 Insure proper termination of data lines.
9 Use isolated repeaters to avoid grounding problems.
7.0 Warranty
Detcon Inc., as manufacturer, warrants each new 1640 Control Unit to be free from defects in material and
workmanship under intended normal use for a period of one year. The warranty period begins on the date of
shipment to the original purchaser and ends one year thereafter.
All warranties are FOB the Detcon factory. Should any product fail to perform in accordance with published
specifications within the warranty period, return it freight pre-paid to Detcon Inc., 3200 Research Forest Drive
Suite A-1, The Woodlands, Texas 77381 for necessary repairs.