User Manual

Chapter 5 DataReader Installation and Operating Instructions
- 58 - Hi-G-Tek Ltd. Micro electro nic s & A sset Tra cking Techno logy
5.6 Cable Selection
The cable is used for power supply to DataReaders in a chain and for RS-
485 serial communication.
For most applications, 3 or 4 pairs of 24AWG shielded cable is adequate.
The serial communication requires shielded twisted pair cable, the power
supply requires low ohmic resistance of the conductors.
Cable connection:
 1 pair for RXA and RXB signals.
 1 pair for TXA and TXB signals.
 SIGNAL GND may be connected to shield or to a pair of wires (shield
connect ion is recommended, t hough it depends on t he noise level of t he
specific environment).
For the power supply: two main issues should be considered: max current
carrying capacity and wire resistance.
Max current capacity: For 24AWG cable, the jacket is heated at 1°C at
0.1A current, max temperature is 80°C. So, this cable can carry a max of
2A at 60°C. ( (80°-60°)*0.1 ).
This calculation should be done for the application specific requirements.
Wire resistance: The voltage drop across the cable may cause insufficient
voltage to the last DataReaders in the chain. Calculation of voltage drop for
the certain setup should be done, in order to avoid this.
In most cases, the solution for such problems can be connecting a pair of
wires for the supply (2 for supply and 2 for return), using thicker cable, or