User's Manual

DataReader Installation
3
Hi-G-Tek Ltd. Microelectronics & Asset Tracking Technology
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Example:
A setup of 10 DataReaders with 20 meter 24AWG cable between
Readers and 24v supply to the first Reader
The ohmic resistance between Readers is 3.4 Ohms (20 meter
of supply and 20 meters of return). Calculating the voltage drop
across the lines gives 5v only, left to the last Reader in the chain.
This is below Reader specification of Reader minimum supply voltage.
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 readers in chain. Calculation of voltage
drop in a certain setup should be done, in order to avoid this.
In most cases, the solution for such problems includes , connecting
a pair of wires for the supply ( 2 for supply and 2 for return), using
thicker cable, or using higher temperature rated cable.
Environmental considerations: In an outdoor installation ,the cable
should withstand all outdoor conditions, that is water proof,
temperature,ruggedness etc.
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 connection is recommended, though it depends on the
noise level of the specific environment).
If two conductors are used for supply and return, the ohmic
resistance would be 3.4/2=1.7 ohm. The voltage to the last Reader
in the chain would then be 17v, well above the minimum voltage
required.
If you experience difficulty calculating the voltage drop across the
supply line, contact your distributor for assistance.