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Sitrans P DS III sensibillity

Created by: Pandiani at: 1/11/2008 6:45 PM (8 Replies)

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1/11/2008 6:45 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 9/4/2024 Posts: 366 Rating: (31)	Hello experts, I need to know about sensibillity of Sitrans P DSIII differential pressure transmitters. I wonder if transmitter is capable to "notice" very short term changes in delta pressure, for instance 100 ms or less? In other words, will change in deltapressure which last less than 100 ms will cause transmitter to change its output current? Thank you.

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1/14/2008 12:28 AM	Rate (0)
Chook Experienced Member Joined: 6/13/2006 Last visit: 9/21/2023 Posts: 201 Rating: (8)	Pandiani Hello experts, I need to know about sensibillity of Sitrans P DSIII differential pressure transmitters. I wonder if transmitter is capable to "notice" very short term changes in delta pressure, for instance 100 ms or less? In other words, will change in deltapressure which last less than 100 ms will cause transmitter to change its output current? Thank you. Hello, The minimum of time constantis 100ms.Youcannot be set lower than this. The current output is depending on the input pressure. Regards chook
	[IMG]http://i17.tinypic.com/66b7jas.jpg[/IMG]
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1/14/2008 5:49 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 9/4/2024 Posts: 366 Rating: (31)	Hello Chook, thank you for your reply. Iknow that transmitter's output (current) depends oninput pressure (differential pressure if such variant is used). Ihave set damping time constant on 0 sec. What I want to do is to try recording input's (pressure) change in very small time. I wonder if transmitter can noticeconsiderable small change in input (say, about 1 %)if that changes last 100 ms or less? In other words, will transmitter's output current will change if there was change in input pressure about 1 % which last very short (100 ms)? I was unable to find data in manual that will definitelyclear my dillema.

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1/15/2008 1:29 AM	Rate (0)
Chook Experienced Member Joined: 6/13/2006 Last visit: 9/21/2023 Posts: 201 Rating: (8)	Pandiani Hello Chook, thank you for your reply. Iknow that transmitter's output (current) depends oninput pressure (differential pressure if such variant is used). Ihave set damping time constant on 0 sec. What I want to do is to try recording input's (pressure) change in very small time. I wonder if transmitter can noticeconsiderable small change in input (say, about 1 %)if that changes last 100 ms or less? In other words, will transmitter's output current will change if there was change in input pressure about 1 % which last very short (100 ms)? I was unable to find data in manual that will definitelyclear my dillema. Hello, You have to connect to your unit to Simatic PDM software via a hart modem and thenlook at the TVT curve ( monitor the current output & respone time)that will help. Regards chook
	[IMG]http://i17.tinypic.com/66b7jas.jpg[/IMG]
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1/18/2008 8:18 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 9/4/2024 Posts: 366 Rating: (31)	Well, I don't have PDM software, so this doesn't help me much. Let's try another approach. In transmitter's manual I have found "transient time (without electrical damping) 0.2 sec". I'm trying to understand full meaning of this. Electrical damping can be set in rang3 (0-100s). If electrical dampping is 0 and knowing transient time, does it mean that transmitter will behave like first order filter with time constant 0.2 sec? If so, it will save time and I won't be needing to order eqipment to record analog output. Can you confirm this? In other words: does "transient time" behaves in same way like damping? Regards, Pandiani
	Last edited by: Pandiani at: 18.01.2008 20:19 Last edited by: Pandiani at: 18.01.2008 20:19
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1/18/2008 9:38 PM	Rate (0)
SonicRanger Posts: 151 Rating: (8)	Hi Pandiani, I think you're approachabout the transient time is right. Sochanges within100 ms could not be recorded. But can you explain what kind of process you have, that you have to measure this quick? Don't you think your process will damp out "spikes"of 100 ms? Another thing: do you think you're analog inputs and controller are quick enough to record these quick changes? Best Regards, SonicRanger.
SonicRanger Posts: 151 Rating: (8)
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1/19/2008 9:28 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 9/4/2024 Posts: 366 Rating: (31)	Basically, I have two pumps, one need to be working all the time, and other is standby. If the first pump fails because of any reason, stand by pump activates. Pump needs to maintain pressure and I have one Sitrans transmitter that is measuring diff. pressure at one point. After first pump stops, second one will turn on in total 200 -300 ms. I need to record how much pressure will drop in this period. I'm sure that analog input card is not fast enough, so I was planning to order oscilloscope to record this change by measuring current output. However first, I need to understand if I have chance to get useful result, and that is by understanding how transmitter works, since I need to record its output. If transmitter is not capable to "catch" this change (I expect pressure will drop no more then 0.5 %) then there is no much sense to continue perfoming the test because probably I'll get false results. Because of internal damping, transmitter will probably show smaller change. However, if I perform this test, I need to know exact transmitter's performance in order to estimate real change in pressure. So far, I have found in manual that internal transient time is 0.2 s, which means that transmitter is acting like first order filter with time constant of 0.2 sec. This means that in case of step change, output will 63 % of input change after 0.2 sec. All I need is confirmation that minimum transmitter's damping (not electrical, this is set to 0 as parameter) is 0.2 sec. Regards, Pandiani

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1/23/2008 9:49 PM	Rate (0)
SonicRanger Posts: 151 Rating: (8)	Hi Pandani, If the specs in the manual are not enough for you, please contact the support department in Karlsruhe. If the manual states this 0.2 secs, I would have no doubt about that (and I would trust the manual more than somebody on a forum who you don't know... ). But I have my doubts if your test makes sense. I think when a pump fails, the pressure will first become fluctuiating and unstable before the pump fails completely, andI think these fluctuations are more than 0,5%. I don't know the kind of pumps you use, but maybe you can consider the sitrans DA400 for your application. http://support.automation.siemens.com/WW/view/en/27028319 Best Regards, SonicRanger.
SonicRanger Posts: 151 Rating: (8)	Last edited by: SonicRanger at: 23.01.2008 21:51
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1/24/2008 6:37 PM	Rate (0)
Pandiani Bronze Member Joined: 10/31/2005 Last visit: 9/4/2024 Posts: 366 Rating: (31)	Thank you SonicRanger, I gave up the tests because after reading the manual and clarifications I got on this forum it was obvious that subtle changes in pressure cannot be captured by this transmitter. Automatic switching logic was implemented in such way that dangerous pressure drops are avoided. Thanks for the help.

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