Air Pressure Regulator for Clamping - PWM?

Hello All,

My project is to perform a simple clamping procedure using a pneumatic pressure regulator and air cylinder. I will be using a microcontroller (possibly Arduino Motor Shield) to control the pressure regulator, which takes a 0-10 V input. I wanted to be able to vary the voltage, though Arduino of course only relies on PWM.

I was thinking of buying the pressure regulator in the URL below (Part number 2859T3). I tried contacting the seller to see if the pressure regulator will work under PWM, but they were not sure. I'm not very experienced with pneumatic systems, so do you think it would be possible for the pressure regulator to register a PWM signal and output the desired pressure? If not, would I need to purchase some DAC device? If so, what would be appropriate?

This, from the link you gave, would seem significant (my emphasis):

As the input signal current increases, the output pressure increases proportionally within the regulating range

Use with sensors that produce the required input signal current

looks like it needs 4-20mA, so pwm + opamp would probably be fine. It probably has a 240 ohm load, so an extra psu of higher than 5v would also be required for the opamp.
An alternative would be a current mirror with gain - try the attached.

The voltage in at the left is an arduino PWM output.
cn1.pdf (15.8 KB)
Pretty much any small signal PNP’s would do - I’d use BC327’s 'cos I’ve got a load of them.
They ought to be matched, but if they’re from the same batch it’ll be near enough.

Note that ‘0’ pwm gives 20mA out, and about ‘180’ gives 4mA ie it goes backwards…

regards

Allan

If you want things the right way up it’ll cost you another transistor…

see enclosed

Allan.

cm2.pdf (18.9 KB)

Thank you for the help, though I am a bit confused. Would the same still apply if it takes an input voltage (0 - 10 V) as the "Input Signal DC Voltage Range" description says?

There are 6 products listed on the page you linked .

5 have a 4-20mA control, for which my circuit would work.

1 has a 0-10 V control, for which it wouldn't.

Which one are you using?

regards

Allan

I am using the 0 - 10 V control (Part number 2859T3)

In which case you need a higher voltage supply - eg 12v -and an opamp.

I append a modified circuit …

regards

Allan

cn3.pdf (20.3 KB)

Hi,

There are 6 products listed on the page you linked .

5 have a 4-20mA control, for which my circuit would work.

1 has a 0-10 V control, for which it wouldn’t.

Which one are you using?

regards

Allan

I’m not sure what page Allan got?
But this what I got.
presreg1.jpg
Tom… :slight_smile:

Oh well... I got a selection. But it looks like the OP needs 0..10V . My appended circuit would be fine.

My current mirror 4-20mA drive (post#2) is quite neat I think, even if he doesn't need it.

regards

Allan.

I see, is there any way I can do this with 12 V or even 10 V, say coming out of the Arduino, using an Arduino motor shield? Also, based on the circuit, I'm assuming the Arduino PWM output is 0 - 5 V?

The motor shield is overkill for what you are trying to do.

You will need a 12v power supply as you can not get 12v form an arduino.

There is a more simple circuit than the one which allanhurst has proposed. Instead of generating 0-5v pwm, running that through a low pass filter, and then taking the output into a 2x op amp, you can simply use the arduino pwm to switch an npn transitor connected to 12v, and low pass filter the output.

You will need to use

analogWrite(pin,255-out);

See this thread for reference

Bilalgp:
Hello All,

My project is to perform a simple clamping procedure using a pneumatic pressure regulator and air cylinder. I will be

Can you say more ?

Why do you need a variable pressure clamp ?
It is a little unusual .

Bilalgp:
. I tried contacting the seller to see if the pressure regulator will work under PWM, but they were not sure. I'm not very experienced with pneumatic systems,

Pneumatics can get expensive quite quickly.
If you explain exactly what you want to do you may get better answers from experienced people here.

(Mechanical arrangements can very quickly exceed the costs involved with arduino projects)

Hi,
Have you also costed into you project a safety release valve?

Tom.... :slight_smile:

Hi cattledog - yes. of course your circuit would work... but the 680/1uF has a time constant of 0.7mS
so would leave an awful lot of ripple with an arduino 1kHz pwm.

Suggest 100uF

regards

Allan

leave an awful lot of ripple with an arduino 1kHz pwm.

I would run the pwm at much higher frequency. It's pretty straight forward to set the prescaler on Timer2 to a factor of 1, for 31.25Khz or 8 , for 3.9Khz and then just use analogWrite() as normal on pin 3 or 11.

We really don't know the voltage/pressure sensitivity of the regulator to know the effect of ripple and how the application plans to change the pressure settings.

If its very sensitive, I would use a 0-5v 12 bit DAC like the mcp 4725 and use the 2x op amp.

TomGeorge:
Have you also costed into you project a safety release valve?

The air regulator already has a relief system. I think that should be sufficient. I am using compressed air provided from a tap at ~60 psi. I am pretty certain of the pneumatics, I am just not sure of the circuitry to control the pressure regulator.

cattledog:
The motor shield is overkill for what you are trying to do.

You will need a 12v power supply as you can not get 12v form an arduino.

Is the motor shield really overkill? Why can't I just use that as a 12 V source? I would like to avoid using a 12 V battery if possible. I am not very adept with electronics, so I'm not sure how to go about this issue.

I was thinking of using a motor shield to control my application to provide the 12 V.

Yes, I suppose you could use a motor shield to supply 12v pwm to a rc low pass filter. You still need a 12v source, but it you want to use the motor shield instead of a transistor, its your money. The signal to the valve is control only and does not draw much current. There is a separate power supply to actually work the regulator. I don't know if such a lightly loaded motor shield will work properly as a voltage source. If you have one, try it out.

How would I be able to use a transistor?

How would I be able to use a transistor?

See reply #11