Pneumatic control & sensor components help

[lnphoenix]

I am tasked to build an in house inflation system. It seems that I get lost in finding required components for my system using Google and the net so I need your expert's help to direct me to vendor & parts.

I need to regulate & monitor a compressed air supply to a constant 12 SCFM and also to regulate & monitor the pressure applied to the unit under test (constant 12 psi) in real time automatically. I'm using National Instruments LabWindows & their DAQ module to handle the user interface. Can you expert in control system to recommend me vendors and components? (integrated components with sensor & control preferred but not required)

Thanks
Lanny

 

[itsmoked]

So what is the inflation source?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[lnphoenix]

It's shop air compressor can produce 19.5 SCFM @100psi.

 

[itsmoked]

I believe you need a run-of-the-mill regulator to control your 12psi. Then you will need a fast flow monitoring device.

I suspect you'll need an orifice with a differential pressure transducer across it. This will give you the flow.

A problem is that typically, your 'inflation' must slow at the end unless you are talking about some sort of continuous blow molding situation akin to extruding.

Here is an ISA doc on related subject matter.

http://www.isa.org/InTechTemplate.c...Management/ContentDisplay.cfm&ContentID=43794

Often you need an "I 2 P" or I/P or "current to pressure" transducer. They take in a 4-20mA current control signal and vary the internal valve to provide the requested pressure.

Perhaps someone with more experience in this subject will come along. Roy?


Keith Cress
kcress -

http://www.flaminsystems.com

 

[lnphoenix]

Thanks for your input Keith.

My inflation system will shut off once the unit under test achieved their inflated pressure but before that, the system needs to deliver constant flow rate at constant pressure, ideally within the range 1.5 to 2.5 minutes.

I know Omega carries these lines but do you know any other suppliers?

 

[itsmoked]

Like I say I haven't done much air control. I did a generator feedwater system that was controlling five horizontal feedwater pumps(1,000psi, 1,500hp each) via I/P's that worked very well, but most pneumatics I do are more on/off pressure controlled.

Fisher is the gold standard in that type of stuff. They were bought by Emerson.

http://www.emersonprocess.com/fisher/products/index.html

The semiconductor stuff I've done, worked at much, much lower pressures than yours.

I know a guy who may have some suggestions. I will see if I can get a hold of him tomorrow.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[JimCasey]

really simple:
The Brooks 1358-8800 is an indicating flowmeter with a constant flow controller. It will handle the flowrate you require. Turn the flow on and off with a slow-opening solenoid valve( quick-open solenoid valve might adversely effect the flowmeter), and monitor downstream pressure with a pressure switch. Turn it on, it runs at a constant flowrate until it hits set pressure and trips off.

 

[dcasto]

You can't have both fixed outlet pressure of 12 psi & fixed flow of 12 cfm. You can have 1 or the other fixed. The way I'd do it is to calculate an approximate downstream pressure regulator size that gives you 12 cfm at 12 psi out and 75 psi inlet when wide open. This regulator acts a a fixed RO that will close only if the pressure gets above 12 psi.

Then I'd put in in place feeding the system and then put a regulator upstream of it that taks the 100 psi stream and cuts it to 75 psi. You can tune the system for flow by adjusting this regulator, maybe set it at 73 psi will give you a better flow or at 80 psi.

 

[itsmoked]

And don't forget a pop-off valve that lets go at 13psi.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

JimCasey; I sure can't find that data sheet. They seem to have a brain dead search engine.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

lnphoenix; As dcasto sez you can't have 12psi and 12SCFM as this ignores what it's connected to. This would be the same as saying "I'm setting up a power supply that will force 12V thru the load at 12A". Sorry, the load has the say in the matter. You can feed it 12V and see what current results, or your can feed it 12A, and see what voltage results, but unless it is precisely a 1.0000 oHm resistor it ain't gonna happen that way.

Your quest is identical. You are not going to attain both your values at the same time. So you need to understand your application to the point that you can correctly choose which is the most important and how, and which variable is the controlled, and which is the contoleeee. It is possible both are controlled at different points in an inflation.


I talked with the gentleman about suppliers.

He suggested Parker Pneumatics precision regulators for the pressure control and Dwyer for the flow monitoring.

http://www.parker.com/portal/site/P...110VgnVCM10000048021dacRCRD&vgnextfmt=default

http://www.dwyer-inst.com/index.cfm

Keith Cress
kcress -

http://www.flaminsystems.com

 

[lnphoenix]

Thanks for the inputs, guys, and especially to dcasto to catch my error. Your suggestion is what I'm looking for. It's like force voltage measure current and clamp the meas current at certain range.

Jim Cassey,

I couldn't find any 1358-8800 manual anywhere at their site. Either it's 1358 or FC8800 and the my first impression is that they are adjustable by hand. It won't work for my application. Hands-free with the exception of using hands for the keyboard.

 

[lnphoenix]

And not to forget to thank the man, itsmoked for provide me tons of materials to read.

I think I have enough ideas & suppliers to pursue my boss' happiness.

 

[sparky970]

You say you can't control both pressure and flow rate. I have a GE moisture meter in our H2 process. Through the factory GE sampling system, it has manual valves that allow you to both set the pressure and adjust the flow rate. Why can't this be done automatically?

 

[roydm]

If you haven't settled on something yet I suggest you look at a Brooks 5850i (current setpoint) Thermal mass flow controller to give you flow control with a pressure control override.
For the pressure control you will need a transmitter, e.g 0-20 psi and a cheap PID controller set up for reverse action. Wire the output of pressure controller to flow controller setpoint. Set the pressure controller output limit to give your required flow setpoint. Because its reverse acting the pressure controller winds up to maximum (flow setpoint). When the pressure reaches setpoint the output will drop lowering the flow to maintain the pressure.

As several others pointed out it's pretty hard to get constant pressure and constant flow if the load is changing.

The Brooks flow controller also has an discrete override input that you can use to turn the system on/off
If you want to get fancy add an indicater to the flowmeter, these are available as an accessory.

Google Thermal Mass Flow Controller and you will find many equal to the Brooks, it's just the one I am most familiar with.

Some need +/- power supplies, the Brooks uses a single supply. You need about 1.5 Amps from memory.

Note: The mass flow controller will also measure the moisture content so you need dry air.
Hope this helps

Roy

 

[lnphoenix]

Thanks Roy. I haven't settle on anything yet. Currently I am looking at Proportional-Air devices and will have a meeting with their Reps soon. I will take a look at the Brooks 5850i.

 

[lnphoenix]

dcasto,

I'm back. The project was put on hold due to priority. Now it's back on my desk and have short time window.

How do you calculate regulator size that gives approx 12 CFM at 12 psi? Is there any equation, java applets somewhere to make my life a bit easier on those things? And also what kind of regulator is it?

Thanks
Lanny

 

[lnphoenix]

Never mind. I dig up the old Crane app note for needed equations.

 

[lnphoenix]

One more thing before I close this thread that yes you can control both pressure and flow simultaneously by using Proportional-Air method as attached

 

[itsmoked]

Not really! You can limit the maximum flow given what the thing you are supplying will allow but it absolutely has to change.

Look at it this way:

You have a big plastic bag the size of a house. You have a regulator that regulates to 12psi you open a big butterfly valve. There is no resistance initially as the bag is deflated. You will get whatever flow the plumbing allows. Say you adjust the butterfly to allow 12CFM at this time. The flow is dictated by the system's resistance with a 12PSI difference across it. Very soon the the bag starts to have a measurable pressure in it. The conditions have now changed, there is no longer a 12PSI difference across the system there is only an 11PSI difference. The flow must therefore change or you need to increase the pressure of the source to 13PSI - meaning the pressure must change.

One or the other for the bag.

Keith Cress
kcress -

http://www.flaminsystems.com