E-Zine January 2016
One of the key resources users could get more from is the vendor that serves them.
Sometimes, it is just because users have pre-existing conceptions about how valuable the vendor community can be. Politely put, users often don’t trust vendors and vendors don’t trust users.
Users vs. Vendors
Users very often are afraid that a vendor will try to push, not the solution that is the best, but rather the solution that makes the vendor the most money.
Vendors are reluctant to spend too much time working on applications because they don’t get paid for it, generally, and they always are concerned that the user will take the advice, solve the problem and buy the products from somebody else.
As you can see, some of this bias (pro and con) is organic. It is based on the reality that most plant engineering personnel do not have the time to specify a product from scratch, and that vendors do lots of that "application level" specifying for free.
The concept that this is for free is reinforced by the ways vendor companies are paid. Reps and distributors are expected to provide application, specification and start-up assistance out of their commission or profit. If they don’t sell the project, all of the application, specification and start-up assistance (yes, sometimes the losing vendor is called on for help at that stage too) come out of their loss.
Yet even more than before, users need the help of quality vendors to make up for the losses they’ve suffered in personnel due to layoffs and reductions in force. Instead of a plant having several instrumentation engineers, many now have one, or a chemical or mechanical or electrical engineer who doubles in brass as the controls person. Sometimes plants have no engineering personnel at all, and are getting by with superior technician level employees, who are stretching to take care of that "higher level."
More next month.
Click here to read “Working with Vendors: Mutual Respect”
From Flow Control (March 2002)
Quiz Corner: Flowmeter Selection
By David W. Spitzer
E-Zine January 2016
The process of selecting a flowmeter for a given application can be complex and encompass the consideration of many diverse factors. One important factor in this process can be an assessment of flowmeter performance.
To upgrade the process, it was decided to add a flowmeter in each of four production lines to measure 0-100 units of flow of Product XYZ with an accuracy of 1%. Two salespersons representing flowmeter manufacturers learned of the addition and contacted the engineer to discuss the application.
The salesperson representing manufacturer A met the engineer for lunch where he/she described flowmeter A as having an accuracy of 1%. The salesperson gave the engineer the latest catalog cuts for the flowmeter best suited for the application.
The salesperson represented manufacturer B came to the engineer’s office for their 11:30 meeting and spent 25 minutes discussing the application. It was determined that flowmeter B, which has an accuracy of 0.75%, would be appropriate. After giving the engineer appropriate catalog cuts, the salesperson took the engineer to lunch.
Assuming that all else is equal (even though we know that it usually is not), which flowmeter should be purchased?
a. Flowmeter A
b. Flowmeter B
c. Neither – call another salesperson (and try to obtain another free lunch)
d. Purchase and install both to see which is superior
What was the basis used to answer the above question?
a. Salesperson was more likable
b. Restaurant selection was superior
c. Flowmeter was superior
d. Salesperson promised tickets to local sporting event
Commentary
In ancient times, all roads may have led to Rome, however in the general case, roads lead in many directions. In addition, following a road provides no guarantee that the traveler will arrive at the desired destination. Further compounding the problem is when the traveler does not know their precise destination. Such is the case above where the problem definition is lacking.
In this particular case, the engineer has not stated the desired accuracy in a precise manner. Questioning the process engineers in the decision meeting would have revealed that the instrument should measure flow within 1% of the actual flow rate. Further, in this continuous process, it would be decided that the flowmeter should be capable of measuring this fluid accurately between 10 and 90 units to accommodate start-up and production.
Armed with a more precise definition of the application, the engineer is better equipped to select the best flowmeter for the application. With appropriate questioning, the accuracy of flowmeter A could be more completely defined as 1% of flow rate between 5 and 150 units, while flowmeter B has an accuracy of 0.75% of full scale between 1 and 300 units. Flowmeter A meets the requirements of the application, flowmeter B does not.
While flowmeter B should be eliminated from consideration, it should not be concluded that flowmeter A should be purchased. While it does meet the minimum requirements, it is not necessarily the best flowmeter for this application. Given that this flowmeter was investigated as the result of an unsolicited sales call, it is likely that other flowmeters exist that would meet the requirements of the application. In addition, many of these flowmeters may perform better than flowmeter A.
How did you approach the above questions? I suggest not purchasing anything until other flowmeters were investigated. If this involves a little more time and another free lunch --- so be it. The long-term results are often worth the effort.
Additional Complicating Issues
Some issues that could complicate the above commentary include applying the flowmeter to a batch process, specifications expressed as a percentage of calibrated span, different specifications at low and high flow rates, independent specification of each piece of equipment, and specifications that ignore hydraulic effects.
From Flow Control (September 2001)
ISSN 1538-5280
How to Calculate Orifice Plate Flow Rate
By David W. Spitzer
E-Zine January 2016
An orifice plate is designed to generate a differential pressure of 1000 mm of water column at a full scale flow rate of 100 liters per minute. What is the approximate flow rate when the orifice plate generates 100 mm of water column?
A. 10 percent of full scale flow
B. 25 percent of full scale flow
C. 33 percent of full scale flow
D. 50 percent of full scale flow
E. None of the above
Commentary
The differential pressure developed across an orifice plate is proportional to the square of the flow. Therefore, one-third flow will generate one-ninth of the differential.
Conversely, the flow through an orifice plate is proportional to the square root of the differential pressure developed. In this case, 10 percent of the differential pressure is developed (100 / 1000), so the flow rate can be calculated as the square root of 0.10, or approximately 31.6 percent of full scale flow.
Answer C is closest to the calculated flow rate.
Additional Complicating Factors
This calculation assumes that the orifice flowmeter is designed, installed, calibration and operated correctly. This is not necessarily the case, especially in gas applications where the gas density is affected by varying operating conditions such as pressure, temperature and composition.
From Flow Control (February 2002)
ISSN 1538-5280
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