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Hello to all,
I wonder if there are people here who know what is the minimum time interval in which dp needs to be change in order change to be caught by the transmitter. It is Siemens Sitrans P differential pressure transmitter, and I wonder if the transmitter itself is capable to "caught" change that last shorter then, say 100 ms?

If anybody knows or have appropriate documentation, I'd be very grateful.

I went and looked-- it isn't in the literature. I would _guess_ that it would see pressure fluctuations on the order of 250 ms. BUT I DON'T KNOW.

In fact, the only people who DO know are your local Siemens representatives.

This, unfortunately, brings up again one of the weaknesses of this forum. What you should do with a specific question about performance in general of a vendor product, is to ask the vendor for a specification. You might come here after that to ask if anybody has seen it not meet that spec.

Try your local Siemens rep.

Good luck,

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
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wboyes@putman.net

Hi,

You can find the manual on the Siemens technical support website. The following link leads directly to the manual:
http://support.automation.siemens.com/WW/view/en/24858290

Kind regards,
David

Thanks, David.

Mikas, if you read deeply enough into the manual David provided, you find that there is a specification called "transient time" which is claimed to be 0.2 seconds, and a factory set damping rate (adjustable from 0 to 100 seconds) of 0.1 second. If I read this correctly, out of the box, the fastest dP change you ought to be able to see is greater than 300 milliseconds. By setting the damping to 0, you can get the transient time down to 200 mSec. But I wouldn't count on it, because there is additional lag time depending on how long the impulse lines are, and other installation related issues. I'd actually believe a half-second response time, probably.

Boy it was hard to find this. It was a whole lot easier to just call the Siemens office and ask them.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net

Guys, thank you for your replies. I did try to get that information from my local Siemens representative, but they didn't know. They couldn't provide me with the answer that satisfied me.

Basically, I got the general answer that output current depends on the input pressure (yeah, right), and that minimal time constant cannot be lower than 100 ms.

Anyway, thank you for the help, thanks to you I found the answer I was looking for.

I've inquired at one point or another of Siemens USA and had them confirm that the internal cycle time on a DS III is 100mS.

A pressure change can occur in the middle of a cycle, that will not be detected and applied to the output until the next cycle, but that's true of any uP device with cycle times.

The user adjustable output filtering, which Siemens calls 'electric damping' can be turned off, that is, set to a value of 0, which offers the fastest input-to-output-response.

I've never been able to get Siemens to define what the manual in section 3.2.3 says is "device internal basic damping":

Electric damping
You can set the time constant of the electric damping in steps of 0.1 s between 0 and 100 s with the input keyboard or set to 0 s. This damping acts additionally to the device-internal basic damping.

David