Connect Tech DFlex-4/104 - Manual (Page 79)

Chapter 4: Appendix H - 20mA Current Loop 4-29
DFlex-4/104 User's Manual, ver. 0.04
To implement a passive interface, wire the transmitter and the
receiver, while leaving the current sources unconnected. An
external current source is required to implement a passive
interface.
To implement an active interface, connect a 20mA current source
in series with the transmitter and another 20mA current source in
series with the receiver. Please refer to Figure 21 for a 20mA
current loop cable wiring configuration between one port of a
DFlex-4/104 adapter and another port of a DFlex-4/104 adapter.
This example shows wiring for both active and passive modes.
When you use a current loop SLIM as a current source in the loop
and the 20mA is flowing, the corresponding LED on the Serial
Line Interface Module will light. If the loop is open or the current
loop SLIM is not used as a current source the LED will be off.
WARNING
When using the current source in a loop with low resistance, the
transistor will run hot. This can be avoided by increasing the
loop resistance. The calculation for Maximum Loop
Resistance(R
L
) is:
Note:
1. S = the number of stations in the loop (TX’s and RX’s)
2. V
D
= the voltage drop for the HP opto couplers on the SLIM.
V
D
= 2.3 V for the HPCL 4100 and HPCL 4200. When you
use other manufacturers’equipment in the loop the value of
V
D
may differ.
Please refer to Table 11 for the pinouts for the SLIM sockets
found on the DFlex-4/104 adapter.
Max R
L
= 22 - ( S x V
D
)
0.020