Three-Wire Transmitters; Voltage Drop In A 2-Wire Transducer With External Power; 3-Wire With Data Logger Power - Campbell CURS100 Product Manual

CURS100 100 Ohm Current Shunt Terminal Input Module
transmitter and everything is fine. However, if the battery voltage drops to 11
volts, a 20-mA current will leave just 9 volts for the transmitter. In this case,
when the battery drops below 11 volts, the output of the transmitter may be in
error.
FIGURE 4-3 illustrates how the voltage available to a transducer (C) is directly
related to the voltage available from the battery (A).
FIGURE 4-3. Voltage drop in a 2-wire transducer with external power
4.2

Three-Wire Transmitters

A three-wire current loop transmitter has the power supply connected directly
to the transmitter. The voltage of the power supply is the voltage applied to the
transmitter. The current output returns to power ground. Data logger ground is
connected to sensor ground and the current output by the sensor must pass
through the resistor before going to ground.
FIGURE 4-4. 3-wire with data logger power
6