Pressure Transducers and Flow Transducers for resisdential u

[user]

Dear all
I am student and working on a project.
I need to implement a test rig for simulating water flow in a small residential unit.
The basic idea is to study the characteristics of components e.g. pressure regulating valve, accumulators by interfacing them with computer.
If any of you have worked in this area, i need assistance in how to select an appropriate pressure transducers and mass flow rate transducers?
Which factors should I consider before selecting an appropriate transducer?

[Doug Hanson]

You need to make sure you have the following covered:
Compatability with transuders construction material & the substance being sensed.
Pressure range.
Burst pressure range
Accuracyt of the sensor required
Output type that is desired from the sensor
Will the sensor provide a good resolution for your PLC requirements
Operating temperature.

http://www.sensata.com/download/ipt_tech-note_2.pdf

[user]

Dear all
Sorry to bother you.
I have one more question regarding sensor selection.
I have a pressure reducing valve (PRV).
As per basic principle, when there is increase/decrease in pressure at the outlet size, the spool inside the PRV will move up/down to keep the output pressure constant.
I need to measure the position of spool relative to its last position. Let's say initially zero, then it lifts up to a new position.
In my project, I am using PRV
http://www.honeywell.sk/public/pages/im ... 7146dc.jpg
I have measured that the distance between the fully open position to the fully close position of spool. It is 10mm.
I need to ask which sensor should I use to measure the movement of spool.
I am thinking to use LVDT position sensor.
But unfortunately I can't figure out how can I install it within the PRV.

If you have any other idea let me know.
Thanks in advance.

[Doug Hanson]

What kind of pressure are you looking at? Using pressure feed back is not enough, you need to know the actual poppet position? You could take the guts out of the valve you posted, have a new body machined up and install the lvdt to contact the poppet at the bottom of the poppet, or you could use a proportional pressure reducing valve with spool position feedback such as this:

[user]

[Doug Hanson]

I couldn't say for sure without seeing the valve in front of me, but I would look at either trying to modify the existing housing so that the appropriate LVDT could thread into the bottom, depending on the lvdt, an oring seal may need to be provided for as you don't want the LVDT housing filling up with water. Also depending on the LVDT used depends on how you attach the rod to the poppet. The ideal way would be to modify the poppet to thread onto the LVDT rod. If there isn't enough material in the housing to drill and thread for the LVDT to attach to, you may need to make a new body (pictured to the right).
I don't really know why you need to know the position of the reducing valve, can you just use two pressure transducers, when the downstream pressure is the same or higher than the upstream side or lower than the set output pressure, the valve is open, when the upstream is higher then the set output pressure, the valve is closed.

[user]

Actually I need to model the dynamics of the valve. That's why I need the position of the poppet with the varying pressure at the outlet side.
Thank you very much for your suggestions.