What is Modulation?

[MHall]

I have heard Modulation used in reference to both boilers and fans, but am still unsure as to what modulation actually is.

Could someone please fill me in on what exactly modulation is, how it works, and its benefits.
Thank you very much

[shogun8]

Modulation is the process of varying one or more properties of a high-frequency periodic waveform or like when a thermostat sends a signel to a controller to make a change in a supply fan speed or a boiler to change from say hi fire to low fire

[timebuilder]

Assuming (oh, boy) that this question applies to the electronics that control fans and bopilers, there are several kinds. Let's look at something with which you might be more familiar.

For example, FM broadcast is "frequency modulation," where the radio emission frequency varies around a "pilot frequency" according to the signal of music and speech coming from the studio. Receivers are designed to look at this variance and convert it to an audio signal. This is demodulation.

AM is "amplitude modulation," there the amplitude (height on paper) or the strength of a carrier wave of fixed radio frequency is changed by the audiop signal that the station wishes to transmit. An AM receiver looks at the changing amplitude and uses that to recreate the audio signal. This is also demodulation.

In circuitry, another type is "pulse-width modulation," where a square wave (an on-off, or high-low type of wave) is changed by altering the amount of time the waveform is in the high or low state. A digital signal buss has a an entire train of these pulses happening at a very high rate, and they are used to transmit data to a group of signal nodes that are connected to the buss. This is how a PC talks to a printer, for example.

In a broader sense, if I change the speed of a fan using a decision circuit such as a P66 controller, which looks at a line pressure and controls fan RPM, I can say that the controller is modulating the speed of the fan.

Can you tell us a little more about why you are asking?

[ewang]

In laymans terms, modulation is the ability to adjust. A simple reference to everyday life; your car's engine. Your foot can modulate the car's power by adjusting the gas pedal. Without modulation, the car would be either On or Off. You can imagine a car without modulation!

Compare this to a furnace. It has a certain "power" or "capacity". With a modulating furnace, the power can be tuned back to use less power, if less is needed. Think about the car analogy. Some days you need less heat than others.