Usually in GT air inlet housing, there are a number of DP sensors measuring the differential pressure across the various layer of filter. However, I always had the question how many sensors at the same layer is enough and does it make a difference where in the housing (top of the housing, bottom, side) you take the pressure measurement.
Also, how is the pressure measurement point tapped into the housing? Through open ended tubing? or some kind of special device?
Thanks in advance.
The tap(s) should be in an area that is not obstructed by any structural steel or any other items which could restrict or block air flow in front of the opening(s). Side- or top penetration is usually best.
As for the method of penetration, I have seen just about every possible method, from a hole burned in the inlet duct sheet metal with a cuttin' torch to which a thread-o-let or weld-o-let was poorly welded and copper tubing was brazed to, to an elaborate pipe coupling welded over a hole drilled in the inlet duct sheet metal, with a Swage-lok fitting screwed in one end into which a piece of stainless steel tubing was inserted.
The biggest issue is the ambient pressure (atmospheric pressure) opening to the differential pressure instrument (switch(es); transmitter(s); etc.). Some vendors used a poro-stone element over the opening to ambient pressure to prevent insects and dust and dirt from entering the tubing and eventually blocking it. But, it needs to be cleaned periodically, which almost never happens. Some vendors have shoved a small piece of green scrubber material into the end of the tubing hoping that would suffice. In a couple of cases there was so much scrubber material shoved in the tubing it was obstructing the measurement. Some vendors didn't provide anything for blocking insects/dust/dirt.
As for the number of redundant sensors (instruments) (I presume that was the question), that's entirely subjective, in my opinion. There can be redundant sensors, but if they all share the same ambient pressure line and that line gets choked/blocked/plugged, they all experience the same degradation in performance. So, if there are redundant sensors there should be redundant ambient pressure ports/tubing/openings--at a minimum, in my opinion, for most optimal performance.
Also, it's very helpful to have a gauge that has decent accuracy and taps in the tubing to which a portable differential pressure sensor can be connected for troubleshooting on the run. The gauge is very useful, and it, too, should have it's own ambient pressure opening/port....
Hope this helps!
>biggest issue is the ambient pressure (atmospheric pressure) opening to the differential pressure instrument
We use a pneumatic exhaust muffler/snubber with a threaded (1/4" NPT) sintered filter that connects into the low side DP port that gets left open to atmosphere for gauge pressure measurements.
It's primarily to prevent mud-dauber insects from making their home in the nice dry sheltered pressure port and plugging the port during and after their construction project but it keeps other dirt out, too.
The mufflers cost maybe $3-$4 each and being threaded can be replaced in seconds. They're widely used in pneumatic fluid power apps.
Thanks for the info and the link. I have seen the sintered iron ones, and they would be very nice, too.
Whatever is used, it needs to be kept clean. I've seen white vinegar used very successfully (hint, hint!).
By the way, I read most of your responses--and you are especially good at providing links, and at taking the time to read the manuals and data sheets for the instruments and devices the original posters are referring to. And, you provide very good and concise information every time. You are to be commended for the quality of your posts, and set a great example for us all!!!