Capilary Remote Sealed Type Level Transmitter

When you examine the calculation (stated below) for LRV and URV values, you need to ask yourself how the calculation takes into account the elevation of the transmitter with respect to datum, the lower tap where the transmitter's high side connects.

How does the transmitter elevation affect, or not affect the calculation?

You asked, so I'll tell give 10 reasons why I answered.

1) The poster qualifies for help.

The OP is not a student looking for an easy out. He's clearly empoyed and working with instrumentation.

2) It's a specific, answerable question.

It's not a lazy man's "what's the calibration procedure for a so and so" which is deservedly a 3-5 pages of explanation answer that is outside what I consider the scope of a forum answer.

3) The topic is relatively common.

I guess I've answered at least a dozen or more questions on "scaling/ranging/calibrating remote seal capillary DP level transmitters" in the time I've been on the forum.

4) The paucity of information on the topic.

I have a collection of 200-300 books specializing process instrumentation, control, and SCADA. I haven't read them all page-by-page but have skimmed them so I know what they do cover. I can't recall where this topic has been covered in detail. To my knowledge, it is only covered in manufacturer documentation, as a setup procedure and then only hit or miss.

Even Tony Kuphaldt's "Lessons in Industrial Instrumentation" book, a massive 3100 page tome (55Mb pdf) available as a free download, while covering hydrostatic level measurement over 42 pages (with great illustrations) does not cover this particular topic in detail. http://www.ibiblio.org/kuphaldt/socratic/sinst/

5) I empathize with those faced with the difficulty finding an exact search term or set of search terms to narrow down a Google search.

I've been there myself. The difficulty in finding answers increases by orders of magnitude when English isn't one's native language. I've lived and worked 'abroad' and run into the language barrier first hand.

6) I understand how difficult it can be to find the information even when it is known that it exists and where it exists.

The particular items I posted were only added to that manufacturer's documentation 20 years after they were involved in the smart level transmitter market. The explanation is only in one document of hundreds that they post on a web site where their own search engine can not find documents even when the exact title or document number is used. They've hidden away a good explanation on a horrible web site.

Anyone like me who has survived through decades of company buy-outs, personnel changes, and 'world class' campaigns knows that documentation is at the bottom of the quality list.

Documentation is a hit-or-miss proposition, varying from era to era, division to division as to what it includes, how it's presented and how it is cataloged.

7). I understand how difficult it is to get a correct answer

I am profoundly aware of how difficult it can be to get a correct answer. Frequently, a Wikipedia 'overview' restates the obvious, becomes encyclopedic in depth or doesn't answer specifics like this topic.

And who hasn't read outright wrong answers or responses that don't answer the question?

Not all answers are equal even when one finds answers. Some are downright useless or unintelligible.

I usually post answers from the relevant manufacturer's docs, not just because it is as close as one gets to an authoritative answer, but to show everyone that the answer is publicly available, as opposed to proprietary information, like DCS control systems, whose documentation is not publicly available.

I have managed to find and keep some of the better examples of correct explanations for process instrumentation issues and, in my opinion, those warrant distribution as widely as possible.

8) It's not just an answer for one guy; today.

These threads have a life longer than the day or week that they're current. CR4 threads show up in Google searches. Any given thread might have, say, 75 hits in the week before it goes stale, but check it 4 years later and it might have 200 hits. The difference is the life a thread has beyond today.

An answer not only helps the OP, it potentially helps an unknown number of others who go looking for an answer.

9) It conforms to my version of the Socratic Method

My version is supposed to make 'em think

a) I prefer to answer with illustrations when available because whoever the Chinese philosopher who said "a picture is worth a thousand words" was right. But even a picture is not always self-evident. Some times you gotta look closely.

b) If you read my answer carefully, you'll see that I don't actually answer the OPs original question. Does the transmitter's elevation change the LRV-URV calculation? I don't really say. It's my Socratic style.

To evaluate requires looking at the graphics and the formula and see the implication of having the transmitter at, or not at, datum.

Maybe the OP will return and ask for clarification. If he does, I'll help him out.

10) An answer lets me rebel against the traditional pedagogical (teaching) method of memorizing an answer to a limited scope question. From my informal survey of questions here and elsewhere on the web and in factory training gigs, it is apparent that the standard conventional technique is to teach a memorized answer to a limited question.

THE most important lesson - how to use the available resources to find and use the needed information, is not taught.

I'm an 'open book' advocate. Find the resource and use it.

I had the great fortune to have had some training classes at VWs Wolfsburg factory decades ago, where the instructors taught the class what reference documentation was available and how it was organized.

Furthermore, the expectation was that the techs were responsible for finding and using the relevant docs in their work. The instructor would not answer questions when the information was in the docs, he'd refer you to the docs. (RTFM before the internet)

Many manufacturers have poor descriptions of their documents, use document numbers which obscure what the document contains, or have so many documents associated with a product that it becomes difficult to assess when doc holds which information.

The OP didn't provide a model number or manufacturer, but all DP remote seal transmitter models use the same formula.

I happen to have good illustrations and I know for a fact that it took this particular major instrument manufacturer over 20 years to include the calculation formula and illustrations in their doc. Even today it is NOT obvious, even to an experienced person where they hide this particular info. But I found it so I posted it for the world to see.