The 4-20 mA pattern can be characterized by the current loop used for the interconnection of the field devices. In this configuration we have that each device must be interconnected with the source and the control device, where we have: on the one hand the A / D converter, used to decode the information that travels in the mesh through the current that flows through it; at the other end we find the sensor device or actuator that should control current flow (sensor) or make use of its value to adjust its parameters (actuator).
On the 4-20mA signals we can list the following characteristics:
- The first 4mA of the 4-20mA signal is used to power the sensor/actuator device. The signal portion corresponding to the control signals is mainly referred to the remaining 16mA of the signal.
- Each device has an operating range, it can be stated that typically devices for the 4-20mA networks use this band for the transmission of information in a linear way.
- Noise immunity. As the transmission through the passage of current through a pair of wires, magnetic fields that reach the cable will induce currents of the same intensity, but with opposite directions, in the cable.
- Transmission over long distances over the standard conductor. This happens due to the principle used in the pattern that is to maintain a current source feeding the circuit, respecting the law of Ohm, the size of the cable has little influence on the transmission of the signal.
- Self-adjusting mesh resistance.
There is a wide variety of devices on the market that are compatible with the 4-20mA standards. We have 2, 3 and 4 wire devices. T
It is important to note that in many insulating applications, used to eliminate ground meshes. There are 2 types of
coupling transformer and the coupling.