What is a sensor, what is a controller, and how do they work together

Almost every facility, workshop and vehicle is full of small devices quietly measuring things. Two kinds matter most here: sensors and controllers.

Sensors measure, a controller gathers their readings, and

Bhairava Sense asks the controller for them.

The sensor: something that measures

A sensor is a small device that measures one thing and reports it. It might be the temperature of a room, the pressure in a pipe, the level of water in a tank, or whether a door is open or shut. What it gives back is a reading: a number, or simply on and off.

A sensor on its own does not make decisions. It only notices.

The controller: something that gathers and decides

A controller is a small computer, usually inside a grey cabinet or panel, that has many sensors wired to it. It collects their readings, remembers the latest ones, and uses them to run the equipment. When a room gets too warm, the controller is what switches the cooling on.

One controller often looks after dozens of sensors. A large site can have many controllers, spread over different floors, plant rooms and workshops.

How they work together

The sensor measures something and sends the reading along its wire.
The controller receives the reading from every sensor connected to it.
The controller acts on what it learns, for example by starting a fan or closing a valve.
The controller keeps the latest reading available for anyone entitled to ask for it.

Why this matters for Bhairava Sense

Bhairava Sense does not talk to each sensor one by one. It talks to the controllers and asks them what their sensors are reading. That is why a controller is the first thing it looks for, and why a sensor can only be seen once the controller it is wired to has been found.

Short version: sensors notice, controllers gather and act, and Bhairava Sense asks the controllers what has been noticed.