The boiler DCS sends an opening instruction, which acts on the actuator on site? How to achieve communication?

There are several ways for DCS to send instructions: one is that 4-20 analog signals are directly connected to the field actuator through cables, which are converted into pneumatic signals to control pneumatic doors through valve positioners, or directly control electric doors, which is a traditional one-to-one control mode, and one signal is taken from one cable to control one door; There is another way, that is, the field bus way. The communication cable signal is a digital signal. One cable can control multiple field devices. It supports many communication protocols, such as prffibus, Fieldbus, modbus and so on. The modbus you mentioned is just one of the communication protocols. There is also a special way to support the hart protocol. Its signal is analog signal plus digital signal.