Automated Proportional Solenoid Valve to Control Aspirating Airflow

I am working on a project where I would like to automatically control aspirating airflow through a valve to a predetermined differential pressure. Through my research so far, I have decided that an ASCO Posiflow Proportional Valve would best suit my needs. The valve operates at a standard voltage of 24 VDC with an operating current of 100-500 mA. The recommended PWM frequency from the manufacturer is 300 Hz.

The manufacturer recommends a control unit for the valve, but it costs $600. We already have a digital system that measures differential pressure and uses an Arduino Mega as the control system. If possible, I would like to use the PWM of the same Arduino to control the valve. Based on what differential pressure is, the arduino would need to increase/decrease the current to the valve until the airflow matches the measured differential pressure. I have examined the other forums related to this on the site but cannot directly relate them to my project due to what I am trying to accomplish and the specs for the valve. I understand I will need to tie in an external power supply to the valve, but beyond that I am unsure of what is needed to control the valve.

Any help would be greatly appreciated. The spec sheet for the valve can be found here: https://www.asco.com/ASCO%20Asset%20Library/asco-posiflow-proportional-catalog.pdf

So basically you want to create a clone of the Asco 8908A001 controller without spending $600?

The data sheet has the voltage and current timing diagram on the second page.

How are your electronics skills?

We are working on the project together and in the planning phase of this project but in short answer, yes. We would like to attempt to build a controller with out spending the $600 if possible. I have been using Arduino for about 2 yrs for various projects but nothing with PWM.

It looks like we could go about the circuit several different ways but in research we could use a mosfet and a 24vdc power supply, and the remaining control circuit. In my experience i have used mostly shields and looks like you could purchase a mosfet shield but we want to make sure we are going about it the right way with some guidance. I haven't done any circuit design but would like to learn more.

For the coil you need a simple low-side or a high-side switch for 24V and 1A. Either a logic level MOSFET with a diode and resistors, or a driver like ULN2003, or a dedicated high-side driver.

The standard Arduino PWM signal may be sufficient, but you can try to program T1 or T2 for 300Hz frequency.

I'm not sure about the software requirements. Aspiration suggests to me varying air flow, in both directions. You must know yourself which values are significant for PID control of the valve.

Reading the datasheet I see nothing about PID or other fancy forms of regulation. All it says is it takes an analog input signal, and produces a PWM output of up to 1,100 mA and 24V. That's one line of code. OK there's a little more to it, as you can set the minimum and maximum current (i.e. duty cycle), and it can do a ramp-up and ramp-down. That's a little bit more code. Still nothing special.

The output is not a simple MOSFET: "Output coil current independent of coil resistance (temperature) and supply voltage variations". This implies a controllable constant current output. Maybe a dimmable LED driver can replicate this, on the other hand a basic MOSFET control should be good enough for your fixed coil and fixed supply voltage.

Following the pressure is not that hard; I don't know if you would even need PID for that, it depends on how quickly your system reacts. Maybe the P part is enough already.

One major question you have to ask yourself: what is the cost of failure? What if your DIY system causes the whole setup to fail, that's now your fault. What is the cost of this? Worth the $600 saving?

They are open loop. From reading it appears that these systems require the solenoid core to be in constant motion so that the coefficient of friction remains constant.

The PWM activation forces a small ripple on the coil that prevents sticking. This is how all proportional valves are operated.

How closely do you want to mimic the mentioned control unit? Is it for your own project only, or do you want to sell your own compatible replacement units?

WVmarle, for our system we would not be doing anything where if the system failed would create a safety hazard. Our thoughts were if we could build a similar circuit and learn along the way that would be great.

We don't necessarily need all the same features as in the ASCO unit, i think if we started simple we could build it up along the way. We don't want to build and sell compatible units, these will end up only being used in-house.

Another question I had was does it matter if it is temperature compensated? In our application our suction flow is constantly varying thus the valve will be constantly moving to obtain the set point.

In search of a circuit to start designing i know there will be various ways to make it. If we go with a mosfet where is a good reliable place to get information on designing and determining components to go along.

Sorry for the delay in responding i thought i had turned on notifications but I never received any....

If you don't know what your specific device should do, who else can know? Actually it's your device, not that of anybody else.

If you provide a complete specification sheet for your device, we can help you to select required components and procedures to implement that functionality.