AutomationDirect DL205 - Current Loop Transmitter Impedance

DL205 Analog Manual, 7th Edition Rev. D
15-7
Chapter 15: F2-8AD4DA-1 8-Ch. In / 4-Ch. Out Analog Current Combination
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Current Loop Transmitter Impedance
Standard 0–20 mA and 4–20 mA transmitters and transducers can operate from a wide
variety of power supplies. Not all transmitters are alike and the manufacturers often specify a
minimum loop or load resistance that must be used with the transmitter.
The F2-8AD4DA-1 provides 100 ohms resistance for each input channel. If the transmitter
being used requires a load resistance below 100 ohms, adjustments do not have to be made.
However, if the transmitter requires a load resistance higher than 100 ohms, add a resistor in
series with the module.
Consider the following example for a transmitter being operated from a 24VDC supply with
a recommended load resistance of 750 ohms. Since the module has a 100 ohms resistance, add
an additional resistor.
In the example, add a 650 ohm resistor (R)
in series with the module.
0V
+24V
DC Supply
Two-wire Transmitter
+--
R = Tr − Mr
R--resistortoadd
Tr -- Transmitter totalresistancerequirement
Mr -- Moduleresistance(internal 100Ohms)
R
= 750 − 100
R
≥ 650
Module Channel 1
R
100 Ohms
IN--
IN1+
Example: