im trying to build a prototype of a ventilator but i am a completely new when it comes to hardware.
to control some other components i need to use a proportional solenoid - specifically im using Gevasol proportional solenoid,like this one: Gevasol P377
it says the are 3 ways to operate this device:
7.1. Current driving [A]
In a coil the electromagnetic force is directly proportional to the current passing through it.
The current drive is therefore, the most favorable method because the influence of the coil’s
resistance variation due to the temperature (self-heating of the energized coil, variable room
temperature) on the voltage will not affect the electromagnetic force.
According to the law of ohm :
U(V) = R(Ω) x I (A)
With a constant current, the flow rate will be stable as long as the entry pressure and the exit
pressure are stable.
To ensure an optimal usage of the valve, do not limit the voltage to its nominal value (shown in
our specifications @ T=20°C), but foresee a factor of almost 1.5x of the nominal voltage
(depending on the nominal power).
7.2. Voltage driving [V]
In this case, you should size the electric circuit to be able to supply a maximum voltage equivalent
to almost 1.5x of the nominal voltage (depending on the nominal power).
7.3. With a PWM (voltage pulse-width modulation),
The frequency should be f >= 3kHz to minimize the « noise » audible to the naked ear and above
all not to create any noise on the flow signal.
The explanation of the voltage drive is valid in this case
now me being inexperienced - how do i decide which method to go for? im using Arduino mega to operate my project.
i read online that its best to use a current control to operate such devices because it is the most stable method - please let me know if its correct and if so - how do i do it?
what is the name of the components i need ? like solid state relay and such so i will be able to deepen my understanding.
preferably i want a through hole components because i will create a custom PCB for my device.
Since you are using an Arduino, the quickest to try is the PWM method. Use a mosfet to do the actual controlling of the power and use the Arduino pwm to control the mosfet. But try each and see which one you like.
The method you use to control the solenoid depends on your requirements, which you have not stated. Proportional valves are finicky, and it is not necessarily straightforward to drive them. Some applications require "dithered" or PID-regulated constant current control, which is not trivial to design.
For example, did you see this caveat from the manufacturer's comments?
If you don't have much experience with electronics or proportional control, then it would be best to buy the manufacturer's controller and get the application working properly, before deciding on which DIY method might be most appropriate.
correct me if im wrong but the PWM freq of the mega is 490 Hz and it states that the freq should be higher than 3KHz. isnt it a problem? also i believe the Arduino isnt capable supplying enough current or voltage (11Volt and 50mA)
So change the frequency.
No Arduino is a power supply!!!! The purpose of the mosfet is to control the PWM of your separate power supply using the PWM signal from your Arduino.
The actual frequency is irrelevant to controlling your shutter. Did you read that they SUGGESTED the frequency to avoid people hearing it? Try it at 490Hz and see if you can get it to work!
thanks for pointing it out , i didn't see that, but as far as i know, my pressure is is stable both in the inlet and the outlet.
giving that this is a final project for my studies, my budget is very limited and given that the proportional solenoid was very very pricey. i doubt they will allow my to buy the manufacturer's controller.
but i will appreciate if you could guide to which alternative is the most suitable for this task in your opinion.
im aiming for a POC here so if this will work "alright" that's gonna be ok for me.
thanks
Correct but the default PWM frequency can be increased. (You'll have to research that, or maybe someone can give you a link.)
3kHz is also in the middle of the audio range, although the valve & mechanics may not tend to resonate at 3kHz. The "traditional" upper limit for human hearing is 20kHz. (Usually only young people can hear that high.)
Also correct. You'll need a voltage source and a driver circuit. (The driver WILL work with PWM.)
oh i believe i understand now - so by connecting the solenoid to the MOSFET which is connected directly to my power source and controlled by the Arduino. is that right?
basically i want to control the pressure by opening and closing the solenoid valve to different levels. and the valve was given to me by my uni - they were able to supply only this one and this is what i got. maybe it wasnt clear but this a medical ventilator.
but by doing so, the Arduino processor will be very occupied with outputting the on off command no? what if it has interrupt? maybe this is not a problem but as i said im new to this so please let me know...
Please do not anticipate problems. Fix them if they happen. Just concentrate on being able to adjust your ventilator! When that works to your satisfaction. Then add new features, one at a time!
