DL205 Analog Manual, 7th Edition Rev. D
4-7
Chapter 4: F2-08AD-1, 8-Channel Analog Current Input
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Current Loop Transmitter Impedance
Standard 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 F2-08AD-1 provides 250 q resistance for each channel. If the transmitter being used
requires a load resistance below 250 q, it will not be necessary to make any adjustments.
However, if the transmitter requires a load resistance higher than 250 q, a resistor will need
to be added in series with the input.
Consider the following example for a transmitter being operated from a 30 VDC supply
with a recommended load resistance of 750 q. Since the module has a 250 q resistor, an
additional resistor needs to be added.
0V
+30V
DC Supply
Two-wireTransmitter
+--
ModuleChannel 1
R
250 ohms
CH1--
0V
CH1+
R = Tr - Mr R - Resistor to add
R = 750 - 250 Tr - Transmitter Requirement
R M 500 Mr - Module resistance (internal 250 q)
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