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SITRANS P DSIII for flow measurement: PRESSURE TO FLOW CONVERSION

Created by: G_R_E_Y_31 at: 2/27/2014 8:12 AM (20 Replies)

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2/27/2014 8:12 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Good Day Experts! This is urgent. Can anyone give me a definitive link on how to parameterize SITRANS P DSIII for flow measurement? In partucular: -What is the conversion formula of SITRANS P DSIII to get flow from differential pressure measurement (this is how it output flow right)? -Should the "Characterization Type" always be "Square Root" if "Transmitter Type" is "Flow" -Is the "Pressure Raw Value" the differential pressure measurement? -There isn't any "area" requirement on the SITRANS parameter right? This is because some SITRANS P DSIII flow measurements in the plant are questioned in reference to a flow measurement using Bernoulli's equation using differential pressure. But I'm thinking that both might actually be equal, but the difference might be on the formula they use on conversion, not on the pressure reading itself. Fow one, the Bernoulli's equation seems to require area on it's equation but SITRANS P DSIII seems not. Any links or FAQs regarding the matter at hand would be greatly appreciated. Please also see: /tf/WW/en/Posts/104609#top Thanks!

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2/27/2014 1:49 PM	Rate (1)
Celsius Regular Member Joined: 1/2/2013 Last visit: 9/27/2024 Posts: 38 Rating: (4)	Hello Nicer,Attached please find the part of our catalog describing flow measurements with a differential pressure transmitter. You will need an orifice plate tailor made for your application. If an orifice and the calculation for the same is not available you will have to refer to the technical support of SIEMENS. You will receive a questionary which is to be filled out so we can provide a suitable solution. Link to the Support Request: http://support.automation.siemens.com/WW/llisapi.dll?aktprim=99&lang=en&referer=%2fWW%2f&func=cslib.csinfo2&siteid=csius&extranet=standard&viewreg=WW&groupid=4000002About your questions:I assume you are dealing with a HART device SITRANS DSIII 7MF4433-*In this case you have to set the application switch to flow. This includes already the Square Root Function.The current output transfer function must be set to “linear”. Otherwise you will have the Square Root Function twice and a wrong result at the output. The pressure value will of course be the differential pressure but the output current will represent the flow.There is no "area" requirement on the SITRANS parameter.The attachment includes a picture of the relationship between the flow and the differential pressure. It is a square root relation and will be calculated exactly like this by SITRANS DSIII. Feel free to come back for more information. Attachment D:\Siemens\Katalog\Katalog_alt\2014\FI01_en_kap03 orifice plate.pdf (551 Downloads)

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2/28/2014 1:03 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Celsius, Thanks for your fast reply! Since I'm currently outside of the plant, if I'm not mistaken, I think it's Profibus PA 7FM4344-. The application is air flow so the element is pitot tube before that was recently been changed to piezometer. And the thing is, it seems there aren't any requirement on the parameter sheet (via PDM) for the piezometer as well as for the tapping point properties/dimensions, would that mean it's not using Bernoulli's equation? Also, will these also be included on the special cases that needs Siemens Support Request? Yap, I guess that the "Pressure Raw Value" (henceforth PRV) would be the differential pressure, but what about the "Measured Value" (MV)? On my bench experiment I found out that the MV differs significantly from the PRV (whether the "Measuring Type" is flow or pressure) and depends on the parameters "Measuring Range" (MR) and "Working Range" (WR). Could you please educate me about these parameters, particularly how would I determine what value to be input to MR and WR? Please also see this: /tf/WW/en/Posts/104609#top Thanks much!

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2/28/2014 5:16 AM	Rate (0)
danw Gold Expert Joined: 3/28/2010 Last visit: 11/8/2024 Posts: 1074 Rating: (214)	What is a piezometer?

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2/28/2014 5:35 AM	Rate (1)
danw Gold Expert Joined: 3/28/2010 Last visit: 11/8/2024 Posts: 1074 Rating: (214)	(Editing function fails again) 1) Primary flow element There are various primary flow elements, orifice plate, averaging pitot tube, venturi, proprietary designs like Taylor wedges or V-cone. A DP transmitter will work with any of these. But you'll have to describe what apiezometer is. I'm not familiar with it. 2) what is the details of the error and DSIII setup where you are seeing unexplained changes? Please provide examples, like: an applied pressure of 40.0 mbar (referenced by an external calibrated gauge) produces a reading in the display of the DSIII of 40.0mbar with an output of 12.0mA representing 40.0 mbar, when the DSIII is setup for linear pressure with a working range of MA at -10.0mbar and an ME at 90.0mbar. Otherwise, it's all speculation as to what's going on. 3) The HART or Profibus manuals can be downloaded. The explanations for flow are quite involved regarding how low flow is dealt with.

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2/28/2014 6:03 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Sir danw, Thanks for your reply! I currently am unable to explain definitively what is that they call Piezometer, but what I've seen on the field is numerous plastic tubes inserted and forms a "ring" surrounding the fan flow measuring point. The SITRANS P DSIII is supposed to measure fan air flow. As I've said, there are found differences on the measured value of the SITRANS with the plant's flow measurement using DP and Bernoulli's formula which considers the measuring point area. So assuming the DP and Bernoulli's measurement are accurate, we are to figure out what makes that difference. Our plan is to first compare the "raw" DP measurement of the plant's DP meter as well as the SITRANS' and if that be found equal, then we conclude that the difference lies on the formula/conversion. So, we are yet to have a tabulated n-point measurement, so I cannot give you your requested example. I'll follow-up immediately. The main settings now are: Input Transmitter Type: Flow Measuring Range: 0-10 mbar Working Range: 0-10 m3/s Characterisics: Square Root Output Process Value Scale: 0-10 m3/s Output Scale: 0-10 m3/s ----------------- So I think I've already answered your question, time for mine: 1) Can you please explain to me what is the "Measuring Range" and "Working Range" for and how do I determine the value to be input? I thought that if you have a PA device, which uses digital signal, there's no need for range/scaling? 2) If I have to get the "raw" DP reading (in contrast to the present flow) for the said plan above, do I have to change the Transmitter Type to Pressure and change the Working Range correspondingly, or the DP reading is already given on the "Pressure Raw Value" I'm seeing when I monitor the SITRANS via PDM? 3) What's would be the difference between "Pressure Raw Value" and the "Measured Value" if I change the Transmitter Type to Pressure and Working Range correspondingly in that both would have the same unit? Please also see this:/tf/WW/en/Posts/104609#top I'll wait for your response. Thanks much!

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2/28/2014 6:10 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Sir danw, Oh I forgot, could you please cite those links about how SITRANS output flow from DP and those parameters seen via PDM (e.g., square root characteristic and material density). Thanks!

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2/28/2014 7:34 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	The exact part number of my instrument is 7MF4434-1FA02-2PC6-Z. I'm yet to found any manual that explains how the flow is converted from differential pressure (e.g., formula) and what exactly are (and more importantly, how to determine) the parameters "Measuring Range" and "Working Range" (since I thought that a digital instrument as this is not supposed to be scaled) which directly affects the "Output/Measured Value" and what is the difference between "Pressure Raw Value" and Output/Measured Value. If you know any links that would help me, please cite it here. Thanks much.

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2/28/2014 7:49 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Sir danw, BTW, why are you asking about the primary element? It seems that there is no parameter setting for the primary element, for I only see "Mechanical Connection" and "Process Connection" on the PDM? Thanks.

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2/28/2014 8:14 AM	Rate (0)
G_R_E_Y_31 Bronze Member Joined: 5/26/2011 Last visit: 8/5/2024 Posts: 456 Rating: (7)	Sir danw, I'm sorry, it turns out that it is not really Piezo, but a Venturi they say. Attachment IMAG0571.jpg (503 Downloads)
	Last edited by: nicer at: 2/28/2014 8:24 AM Please see attached file for the air flow primary element.
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