Pressure Scanners

There's no reason you need to have multiple transducers, as you say you can build a pneumatic array switching one pressure transducer between several pressure lines.

It does mean that you will not be able to monitor all the pressure lines at the same time and that cycling through the selection of pressure sources will take a bit of time.

But if that's okay with you then a single pressure sensor going to a single pressure measuring device with a bank of solenoids switching is fine. Bear in mind that the reliability of all those pneumatic solenoids will reduce the life of the system though.

John.

Thanks John,

Do we need to make such a system of solenoid valves or can this be bought out? If these can be bought out, then what are these called? Could you help me out by suggesting some companies that do this kind of work? The next question I guess we would have to answer is what would be the time scale between measurements between different pressure lines. The answer to that question would depend upon the length of the pressure lines and how long it would take for the flow pressure to be stabilized in a given line. Am I correct in assuming this? I guess solenoid switching frequency won't be an issue as the pressure lines are expected to be quite long in our case (~2m).

The question about solenoid reliability impacting the system reliability is also something we would be focussing on next.

Thanks for your thoughts. Looking forward to hearing from you again.

What you're suggesting is going to problematic. You propose to use a single pressure transmitter and switching the impulse lines to different vessels, pipes or whatever.

For one thing, when you switch over to a new line, you'll have to wait for the pressure to stabilize and that might take anywhere from several seconds to minutes depending on the length of your lines.

Next, your lines would need to have equal lengths and sizes. If they're different, the settling times will be different from one point to the next.

Finally, I don't know if the spaces you're measuring the pressure from have compatible atmospheres. What I mean is, if vessel 1 contains, say oxygen, and vessel two contains some flammable gas.

If the pressures are small, you can get those small pressure transducers from Dwyer. They're less expensive than the industrial types. You'll need multiple analog inputs to your PC or PLC to record the data but you can buy those as well.

Thanks Vulcan,

The problem we are facing is that the pressures to be measured are quite small(~5 psi) and high accuracy is required. I quickly went through the Dwyer website, but it seems that the range of pressures handled by them are all > 15 psi. Of course, I need to check it out in greater detail and thanks for the reference.

The only plus here is that the fluid is air in all pipes so the issue of oxygen and flammable gas doesn't arise. We can in principle use the same transducer for all lines.

The demand for low pressures and high accuracy result in expensive transducers. We also need to measure pressures from a high number of lines (>100). With the above two problems the obvious answer is a pressure scanner, but this is an expensive option. If we instead go for a system wherein we switch between different lines and we allow enough time for the flow to stabilize, we can manage with fewer transducers.

We would of course have to weigh the issue of time required for measurements with respect to the cost of running the set up.

But, I just wanted to know if this is something people do in the industry and is there an off the shelf alternative to the expensive pressure scanners.

Thanks Again.

Ahhh low pressure and high accuracy - the two things that make pressure sensors expensive!!

Glad to hear there's no contamination problem with different gases etc...

I have designed and built a number of these type of pneumatic multiplexers, mainly for air gauging systems, so that one air gauge (low pressure pressure sensor etc..) can be used to measure several pressure measuring points accurately, so I would agree with the basic idea of pneumatic switching, but it has to be done carefully, to allow settling time as well as any problems with turbulence or whatever.

The pneumatic valves I have used for these instruments have ranged from rather expensive and power hungry valves to miniature valves that are reasonalby cheap and are easy to replace, if you want any further information either ask on here or drop me an email using the personal messaging service on here.

John(at)marchdesigns.com

it seems that the range of pressures handled by them are all > 15 psi...I need to check it out in greater detail

There are models that can go down to 1 inch of water (<1 psi) and models that cost less than $100. The price depends on accuracy and range. You didn't state how accurate you needed to be.

I haven't worked or seen such a pressure scanning system before. They're probably rare because of the issues I stated earlier. You may also have problems if the some lines have different temperatures from the others (e.g., exposed to the sun vs in the shade).

Good luck on your project. 'Sounds interesting.

Below is the company we deal with to measure pressure. We have tried pressure transducers, but found the pressure film to be much better for our applications.

Applications Specialist (Pressure is our Business)

Sensor Products INC. USA

300 Madison Ave.

Madison, NJ 07940

1.973.428.8985 (phone)

1.973.884.1699 (fax)

vshalyt@sensorprod.com

I installed a Scanivalve system 20 years ago and as I recall it had multiple inputs that were scanned and the pressure sent to one built in transducer that sent at that time sent an analog sigmal straight to the console computer. This system is not built any longer but the new arrays that scanivalve has now seem , by looking at the website, to function in the same way. Looks to me like an array of 16 port systems would do you job with the accuracy you desire.

Thanks everyone.

Pressure accuracy expected is 0.2% of full scale.

Scanivalve website mentions that they have stopped manufacturing the earlier range of products, I have sent across a request for more info, but I think we will be getting a response in the new year due to Christmas and new year vacations.

Scanivalve manufactures products that can be used for scanning different pressure signals. However, they have one pressure sensor per port. This results in 32 pressure sensors for 32 ports. There is a facility for duplexing and using the same pressure scanner for measuring 64 signals. But I was curious if this could be done more economically.

Shall keep you posted as I find out more.

Thanks Again