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I wish I knew what a field network is!
When you have field devices sending data to your control system and the control system sending data to your final control elements, you need a standard communication between all these devices to control your product – in short, a field network.
In the past, we used a pneumatic signal, best known as 3-15 psi, to transfer the data. Later, analog entered the field, and 4-20mA, 1-5 volts, and their variations started to pop up. Now we have a variety of digital options as well.
Analog remains popular, even with all the digital options, because of its robustness and easy troubleshooting. However, years ago people in the industry realized we needed more data from those devices. So they created HART, a digital communication protocol for an analog network. You can read more about that here.
HART is popular to set up devices, but as a form of communication it never got a warm reception. However, it’s still an option, depending on the application.
Once the first pure digital protocols arose in the market, industry experts created field networks to read all your field devices, controllers, and final control elements.