AMC VersaTox, Инструкция по эксплуатации

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4.3 CABLE SELECTION
There are three occasions when cable selection is needed; they are explained in the following
sub-sections.
4.3.1 2-WIRE 4-20 mA DC POWER LOOP
A two conductor, shielded cable is recommended to transmit the 4-20mA signal from the AMC-
VersaTox sensor/transmitter to the monitor. The same wire pair is used for both signal and
power due to the low power current loop design of the AMC-VersaTox. For best signal
transmission and maximum noise rejection, it is recommended to run the cable through steel
conduit (the cable shield must be grounded at the monitor or power supply).
The figure below is an aid for wire selection. There are three variables that determine the
maximum cable length; wire gauge, power supply voltage, and load resistor. The purpose of the
load resistor is to covert the current signal into a voltage signal. Three common load resistors,
100
Ω , 250 Ω , 500 Ω are used in the graph with 12 and 24VDC power supplies and a wire gauge
range from 22 to 16 AWG. All the curves include a safety margin of 0.5VDC. The user must take
responsibility for the selection of wire gauge, power supply voltage and load resistor used as the
values shown may not be suitable for all applications.
2 Wire Cable Selection
100R 12V
100R 24V
250R 12V
250R 24V
500R 24V
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
22000
24000
26000
28000
30000
16 17 18 19 20 21 22
Wire Gauge (AWG)
Cab
le L
e
ng
th
(
F
eet)
Figure 4-15 2-Wire Cable Selection Graph
(Based & V
SM
= .5 V)