# What happens if We change the frequency of Pulse Width Modulation

#### datdang

Joined Feb 21, 2023
23
Hi everyone,

Some hydraulic valve system use Solenoid to control the flow of Hydraulic. The electrical signal supplied to Solenoid could be both DC voltage or PWM ( Pulse With Modulation). The question is what happens if we change the frequency of PWM , for example if we change the frequency of PWM from 100 HZ to 330 HZ , how that affects the operation of Solenoid ?
I made a experiment to supply same DC current (1 A) to both 10 ohm Solenoid and 10 ohm resistor. Could anyone know why the heat generated from 10 ohm Solenoid is not so much compared with the heat from 10 ohm resistor Thank you so much

#### Papabravo

Joined Feb 24, 2006
20,384
If you take the integral of a signal over one period and you get a certain result. Do you change the result if you change the period?

#### datdang

Joined Feb 21, 2023
23
If you take the integral of a signal over one period and you get a certain result. Do you change the result if you change the period?
I have not change the period , I'm not authorized to change the period because It could harm the operation of Solenoid that could lead to a malfunction of whole system .

#### Papabravo

Joined Feb 24, 2006
20,384
I have not change the period , I'm not authorized to change the period because It could harm the operation of Solenoid that could lead to a malfunction of whole system .
Isn't changing the frequency the same thing as changing the period. You asked the question, and I could care less what you are or are not authorized to do.

#### ronsimpson

Joined Oct 7, 2019
2,748
Could anyone know why the heat generated from 10 ohm Solenoid is not so much compared with the heat from 10 ohm resistor
I think the resistor is much smaller than the solenoid. That is why the resistor is hotter.

#### crutschow

Joined Mar 14, 2008
32,899
The question is what happens if we change the frequency of PWM
The average voltage of the PWM signal is determined by its duty-cycle, so changing the frequency with the same duty-cycle should cause no appreciable change in the solenoid operation.

As the frequency gets lower, you will reach a point where the solenoid starts to buzz.

An increase in frequency will increase the switching losses in the electronics generating the PWM, which can become significant at higher frequencies, depending upon the design of the driver.

#### datdang

Joined Feb 21, 2023
23
The average voltage of the PWM signal is determined by its duty-cycle, so changing the frequency with the same duty-cycle should cause no appreciable change in the solenoid operation.

As the frequency gets lower, you will reach a point where the solenoid starts to buzz.

An increase in frequency will increase the switching losses in the electronics generating the PWM, which can become significant at higher frequencies, depending upon the design of the driver.

#### Tonyr1084

Joined Sep 24, 2015
7,454
I think what would be more important is the speed at which the solenoid valve can operate. Switch it between open and close faster than it can switch between those two states would mean the valve would tend to float in a more open or more closed position but never achieve full travel between open and closed.

I'm no expert on PWM. But I believe the intent is to switch something on and off fast enough that you don't get noise but rather get an average voltage between the on time and off time of each period. That's usually done at high frequencies. I've heard 20KHz is not uncommon for electronics regulation. But for a mechanical valve I'd have to guess and say 100Hz is probably the best rate for a slow slewing valve. By "Slow Slewing" I mean a valve that can take milliseconds to open or close as opposed to something that can slew in microseconds.

In the end I believe that if you open and close the valve too fast it will become an ineffective control with unpredictable results, which could mean damage to machinery, property or personnel. If one were to attempt such a modification it should be done under very tight and safe control with the understanding that something like a hose could be blown out from over-pressurization.

#### MisterBill2

Joined Jan 23, 2018
15,630
As long as the frequency of the PWM drive voltage is high enough so that the valve can not follow it, there will not be much effect except that the effect of the inductance on the impedance will cause the current to decrease a bit. If the frequency becomes close to the mechanical resonance frequency of the valve, it might become noisy.
And of course the resistor will get much hotter than the valve because the same power is spread into a much smaller mass.