10 Determining the maximum load resistance
at the 4 … 20 mA interface
The load resistance connected to the OTT CBS must not exceed a specific maxi-
mum value. This value depends on the level of the supply voltage of the OTT CBS.
If the load resistance is greater, the output current can no longer be evaluated.
Smaller load resistances are allowed.
䡵
Read off the maximum load resistance for your power supply from the
following diagram.
Example:
Power supply 18 Volt
→
max. load resistance 450 Ohm.
The OTT CBS delivers an output current corresponding to the measured value
for a load resistance of up to 450 Ohm.
䡵
Dimension the connected electrical circuit accordingly. Check the input
resistance of the connected peripheral device for this purpose.
10
15
20
25
30
U
V
100
0
200
300
400
500
600
700
800
R
Ω
900
1000
Exa
m
ple
Fig. 21: Diagram to determine the maxi-
mum load resistance as a function of the
power supply.
Minimum power supply: 10 V
Maximum power supply: 30 V
Resistor tolerance: 0.1 %/15 ppm.
24