User`s manual

RabbitFLEX User’s Manual www.rabbit.com 55

4.3.13.3 Analog Input 4-20 mA

This section presents the circuit schematic and the characteristics for the 4-20 mA analog input.

This analog input provides a simple interface for industry standard 4-20 mA devices. It is a passive input

and the device must either supply the loop current or be wired in series with a supply to operate correctly.

The loop is formed by using the input pin as the SIG+ line and the ground pin as the SIG- or signal return.

A design consideration for choosing the appropriate ADC circuit for your application is the fact that cur-

rent is preferred over voltage in noisy industrial/control environments where the transmission of low-

amplitude, low-frequency signals must travel significant distances. This is because the current stays con-

stant over the length of the cable.

Figure 4-27 Analog Input 4-20 mA Circuit Schematic

Table 4-23. ADC 4-20 mA Characteristics

Analog Input, 420 mA

VERSION 6.01

2.2 kW

10 nF

100 W

I/O

Analog Input

Cell