3/9/2014 5:18 AM  
Joined: 5/26/2011 Last visit: 4/30/2018 Posts: 359 Rating: (6) 
Hi sir danw! How are you doing?
I'm getting your point, but it seem to assume that the only way to accurately measure flow is via DP or through something at least as complex as it. Now, the process dept. has what they call "Anemometer" which seems to directly measures flow using something like a small propeller. They insert it on the inlet air duct sampling hole. Actually, this is where they get what they call a "coefficient" for their Bernoulli's equation for converting flow via DP (measured by manometer) which, they say, is a constant (for each fans/flow element) for the deviation to the standard process enviroment. And this is also why I'm considering their calculation using Bernoulli's equation since,as they say, their flow calculation from DP (with the coefficient) coincides with the Anemometer on five points! First, they would determine this coefficient from the deviation of their calculated flow from DP (via Bernoulli) to the flow (via anemometer) reading. It first seems circular (they literally compensate for the deviation by this coefficient) but when I ask if their DP to flow calculation,using the same coefficient,would still coincide on different flow points with the anemometer, they answer positively, which means, if the anemometer reads accurately, then so is their calculation/formula. But I also wonder on the validity of that seemingly simple plug and play anemometer. I'll ask them if, aside from the digital reading, they would also have some calculation that consider some other factors such as element characteristic and process condition. For if so, then you would be correct that it is may be meaningless. And if not, then it's also a good question why they don't implement that rather than DP.
Ahm yap, since that's (Measuring & Working Range) the very variable that represents the calculated characteristics. Now, let's assume this happened, that is, their anemometer is accurate and the SITRANS with Measuring & Working Ranges from a sizing sheet calculation deviates in reading, what would we do? If I understand it correctly, we would revise the Measuring & Working Range with respect to their independent flow & DP reading, right? If so, then, let's say on one point they measured 10mbar (via calibrated manometer) and a corresponding 15m3/s (via anemometer), if I understand you correctly, we can already use this as our Measuring (010mbar) and Working (015m3/s) Ranges, since it would already represent the DPflow correspondence/characteristic of the current flow element & conditions. Any change in actual flow upward or downward would just be an extrapolation from this.
I see, but how about their calculation using Bernoulli's equation that seems to not consider any ranges/characteristics, only the measured DP, density, area, and a coefficient, which coincides with an independent and seemingly direct flow measuring device (anemometer)? They seem use the formula as an alternative on how the formula the SITRANS and, as you said, every flow transmitter that uses DP as primary variable uses. Actually, their calculation (and anemometer) also coincides with the SITRANS conversion on five points (albeit having a tolerable <5% error)! Athough partly because we first adjusted the range exactly for the latter to coincide with the former (talking about reverse range determination, but this is worse because it's trial and error since I haven't yet realized yet there that it's better to use their DPflow measurement as the Measuring & Working Range at least for the purpose of being close to them since their calculation appear to also generate similar curve), but it's a different story when it coincides with five points. Would this mean that, not only their calculation has some validity as an alternative DP to flow conversion (it also formed a curve close to the SITRANS formula), but also their flow DP element (simply some holes around the air inlet duct that is joint together as a ring, which viability has been questioned) because, at a certain flow points (via anemometer), it's able to generate the DP that corresponds to a characteristic (i.e., again, extrapolatable by the SITRANS formula)? The coincidence of their calculation from DP to flow using Bernoulli without characterization/ranges,the SITRANS conversion from DP to flow using characteristization/ranges, andtheir direct anemometer measurement without DP seems to tell something. But I'm also thinking, maybe it's only becuase we're only measuring on small intervals on a small range (5 points lies within <8mbar manometer and <10 m3/s anemometer), and wouldn't work when taken on higher points (I'm almost sure of this for the trial & error reverse range determination part!). Lastly, can I ask for an actual example of this "sizing sheet" that has generated a particular Measuring & Working Range, and if possible, including the very calculation? You've really been a big help to me, I'll await for your continuous response. Thanks again! 
Last edited by: nicer at: 3/9/2014 10:56 AMLast edited by: nicer at: 3/9/2014 5:35 AM 

2/8/2016 4:32 PM  
Joined: 9/3/2014 Last visit: 2/16/2018 Posts: 5627 Rating: (119) 
New question published by hashemi teimoor is split to a separate thread with the subject SitransP, Simatic PDM 6 could not read value or write parameters to device. Best regards 
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