1-332

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

R3 in Figure 18.

Length of current loop (one

direction) versus minimum

of the circuit in Figure 18 is

graphically illustrated in Figure

19. Multidrop configurations will

predicts in order to account for

additional station terminal

voltage drops.

Typical data rate performance

versus distance is illustrated in

Figure 20 for the combination of

a non-isolated active transmitter

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

(0000001011111101) was used

for data rate distortion measure-

ments. Data rate is independent

of current source supply voltage,

The cable used contained five

pairs of unshielded, twisted, 22

AWG wire (Dearborn #862205).

Loop current is 20 mA nominal.

Input and output logic supply

voltages are 5 V dc.

Full Duplex

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.

As Figure 21 illustrates, the

combination of Hewlett-Packard

current loop optocouplers, HCPL-

4100 transmitter and HCPL-4200