Pneumatic control & sensor components help
Pneumatic control & sensor components help
(OP)
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
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





RE: Pneumatic control & sensor components help
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pneumatic control & sensor components help
RE: Pneumatic control & sensor components help
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.
htt
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
RE: Pneumatic control & sensor components help
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?
RE: Pneumatic control & sensor components help
Fisher is the gold standard in that type of stuff. They were bought by Emerson.
http:/
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
RE: Pneumatic control & sensor components help
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.
RE: Pneumatic control & sensor components help
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.
RE: Pneumatic control & sensor components help
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pneumatic control & sensor components help
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pneumatic control & sensor components help
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:/
http://www.dwyer-inst.com/index.cfm
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pneumatic control & sensor components help
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.
RE: Pneumatic control & sensor components help
I think I have enough ideas & suppliers to pursue my boss' happiness.
RE: Pneumatic control & sensor components help
RE: Pneumatic control & sensor components help
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
RE: Pneumatic control & sensor components help
RE: Pneumatic control & sensor components help
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
RE: Pneumatic control & sensor components help
RE: Pneumatic control & sensor components help
RE: Pneumatic control & sensor components help
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
RE: Pneumatic control & sensor components help
Sorry I haven't checked in on this thread recently.
For those who could not find the data sheet:
http:/
Yes, the knob is set manually. Set it at 12 and forget it. The 8910 is a separate device, sold tubed to the meter. It holds a constant flow as the pressure changes.
As I envision the system: Regulate the pressure to 12 psi.
Run the flow through a slow opening solenoid valve. Thenn the flow goes through the brooks flowmeter. You want the solenoid not to pop open too quickly because when it first begins to open, the orifice in the flow controller will be wide-open. Hit it too hard and you could shoot the rotameter float against the upper stop and make it crack the glass.