Its because a gas furnace is usually either on or off. It could be used for electric heating because the wattage going through the heating elements can be adjusted within a certain range. I’m sure facilities that need to store things at an exact temperature use it.
Thanks for your video. Can I ask if D and I have both positive or negative values? For example if d is the rate of change of error, however , in your case, the error can be 5 cellcius degree higher or 5 cellcius lower than the setpoint value. What I am trying to say is, does error have directions? or it is just a absolute value.
I don't know for sure, but I don't think so. The P, I and D is the coefficient you multiply the error by. The direction of the error (positive or negative) is accounted for by if you are over or under the target value. In the case of D its if you are making meaningful progress moving towards the target (positive) or away from the target (negative).
You wouldn’t want values that push the output away from the target. The coefficients associated with the P and I terms are always positive while the coefficient associated with D term is always negative. Gain refers to the absolute value so the numbers entered for P, I, and D are always positive. The terms themselves can be either positive or negative (since the offset of target relative to the output can be either positive or negative).
