Figure 17. Simplex Current Loop System Configurations for (a) Point-to-Point, (b) Multidrop.
and OFF states. This non-isolated
active transmitter provides a
nominal 20 mA loop current for
and HCPL-4200 optically coupled
current loop receiver shown in
Figure 18. Curves are shown for
10% and 25% distortion data
rate. 10% (25%) distortion data
rate is defined as that rate at
which 10% (25%) distortion
occurs to output bit interval with
respect to input bit interval. An
input Non-Return-to-Zero (NRZ)
test waveform of 16 bits
Input and output logic supply
voltages are 5 V dc.
the listed values of V , R2 and
Full Duplex
CC
R3 in Figure 18.
The full duplex point-to-point
communication of Figure 21 uses
a four wire system to provide
simultaneous, bidirectional data
communication between local and
remote equipment. The basic
application uses two simplex
point-to-point loops which have
two separate, active, non-isolated
units at one common end of the
loops. The other end of each loop
is isolated.
Length of current loop (one
direction) versus minimum
required DC supply voltage, V ,
CC
of the circuit in Figure 18 is
graphically illustrated in Figure
19. Multidrop configurations will
(0000001011111101) was used
for data rate distortion measure-
ments. Data rate is independent
of current source supply voltage,
require larger V than Figure 19
CC
predicts in order to account for
additional station terminal
voltage drops.
V .
CC
Typical data rate performance
versus distance is illustrated in
Figure 20 for the combination of
a non-isolated active transmitter
The cable used contained five
pairs of unshielded, twisted, 22
AWG wire (Dearborn #862205).
Loop current is 20 mA nominal.
As Figure 21 illustrates, the
combination of Hewlett-Packard
current loop optocouplers, HCPL-
4100 transmitter and HCPL-4200
1-332
HP [ HEWLETT-PACKARD ]
