A Cloud In TheSky

Controlling the environment in a room can be tricky. Often it's based on an economic viewpoint. I will try explaining different sensors and outputs and what I've seen used practically with good results.

I will try explaining “Best Practice” or “Ideas of best practice” below with increasing advancements.

Simplest automation, is a room temperature sensor controlling room heating. Heat setpoint at 23 °C, and when room temperature gets below this setpoint, you can start regulation your heat option.

Regulators can be a difficult subject that requires a comprehensive explaination. For now I'll just explain 2 types.

Control curves can be 2 points and upwards (Often no more then 10 points) For heating, imagine 2 points in a curve, where X is the temperature below setpoint eg. 10 to 0 degrees below, and Y is a percentage from 100% to 0%. See the graph below.

PID regulators is a bit more difficult to explain and understand. They use more system resources so often the control curve is preferred if the system is low on resources.

I'll try a simple explanation first: If the temperature (Control variable) gets below setpoint, the regulator will increase the heating (Output variable)

There's in a basic PID regulator, 3 variables, proportional gain (P or P-band), integral gain (I or I-time) and derivative gain (D)

You can use 3 methods, P, PI or PID

A P-regulator, will measure the “error” from ( setpoint - control variable ), if setpoint is 23 and control variable is 20, the “error” will be 3. It will then take the output variable and add the error. If the output was 0, after the calculation it will be 3. Thus the P regulator, as seen in below picture as blue, will never reach it's setpoint.

On Wikipedia there's a lot of information about this regulator, but I will highlight one thing from there, a pseudo code examble.

• Kp - proportional gain
• Ki - integral gain
• Kd - derivative gain
• dt - loop interval time
• previous_error := 0
• integral := 0

loop:
error := setpoint − measured_value
proportional := error;
integral := integral + error × dt
derivative := (error − previous_error) / dt
output := Kp × proportional + Ki × integral + Kd × derivative
previous_error := error
wait(dt)
goto loop

A sensor is basically anything inbound information, from temperature to light status.