High End Systems Technobeam manual Constructing Cabling, Terminators

•maximum capacitance between conductor and shield - 55 pF/ ft.

•maximum resistance of 20 Ω /1000 ft.

•nominal impedance 100–140 Ω

•22–24 AWG with insulation having a dielectric rating of 300 volts or higher

For example, Belden® 9841 data-grade cabling meets specifications for EIA RS-485 applications and is highly recommended (or its equivalent) for use with Technobeam.

Constructing Cabling

If you need to construct cabling, you must use a shielded, two- conductor cable with a male 3-pin XLR connector on one end and a female 3-pin XLR connector on the other end. Pin 1 is the common (cable shield), pin 2 is the data complement (negative), and pin 3 is the data true (positive).

Figure 2-3. Properly-constructed data cabling.

You should test each cable with a voltage/ohm meter (VOM) to verify correct polarity and to make sure that the negative and positive pins are not grounded or shorted to the shield or to each other. Also, make sure that pin 1 is shielded.

Caution	Do not connect anything to the ground lug
	on the XLR connectors. Do not connect or
	allow contact between the common (cable
	shield) and the fixture’s chassis ground.
	Grounding the common could cause a
	ground loop and/or erratic behavior.

Terminators

The last device on each link must have a 120 ohm, 1/4 watt (minimum)

Technobeam® User Manual Overview of Controller Operation 2-5