E-Zine February 2016
Click here to read “Working with Vendors: Potential Conflict”
The seemingly confrontational relationship between vendors and users was discussed last month. However this need not be the case.
Because this is a bi-directional issue, it is up to both the vendor and the user to do what is necessary to make sure that the relationship between users and vendors provides the most value.
The key is to understand the way the relationship between users and vendors should be.
What works is to create a relationship of mutual respect and trust.
This is not the same thing as becoming friends. Many vendors think that they need to be “buddy-buddy” with their customers, and then the vendor gets understandably upset after taking them to the ballgame, playing golf, buying meals and all the standard friendship building things vendors often do, the customer buys the product from somebody else.
A professional relationship of mutual respect and trust is built on the acknowledgement from both sides that each party has value to contribute to the relationship.
Establish Guidelines
Regardless of how competent an engineer or technician you are, the vendor’s technical people are certain to know more about the product you are using than you do. Regardless of how competent a vendor rep is, it is certain that the user is bound to know more about the process into which the product must fit than the vendor does. If we recognize that, we can move quickly to a professional relationship of mutual respect and trust by following some simple rules.
More next month.
Click here to read “Working with Vendors: Guidelines”
From Flow Control (March 2002)
Details, Details, Details… Knowing the Whens and Whys of Measurement Lead You to Solution Success
By David W. Spitzer
E-Zine February 2016
Raw materials for processes can be expensive. Using 1 liter per minute of a raw material that costs US$ 1.00 per liter represents an annual expenditure of over US$ 500,000. Many raw materials are used in higher quantities and some are more expensive, so total annual expenditures can easily be many millions of dollars. On the other hand, water flowing at a low flow rate can be relatively inexpensive. However it is often important for operating companies to precisely measure and control the use of raw materials because sometimes a small and inexpensive flow can have a large impact on the process.
There are many technologies that can be applied to measure the flow of raw materials such as Coriolis mass, differential pressure, positive displacement, and vortex shedding flowmeters. Which technology would you select assuming that all of these technologies will operate reliably in the service? How would you analyze this problem?
The overall objective is to feed the correct amount of raw material to the process. Feeding too much or too little will have adverse financial and/or operational consequences. Feeding the correct amount of raw material requires precise measurement of its flow. Therefore, the measurement objective might be to measure the flow of raw material as accurately as possible.
Each potential technology can be evaluated and compared based upon its accuracy in the application at hand. Coriolis mass and positive displacement flowmeters generally offer better accuracy than either differential pressure or vortex shedding flowmeters in liquid applications. Coriolis mass flowmeters have the advantage of measuring mass flow but positive displacement flowmeters can measure high viscosity liquids with relatively low pressure drop and high accuracy.
In many applications, positive displacement and Coriolis mass flowmeters will perform similarly. However, in other applications, one or the other may be clearly superior.
From Flow Control
Which is more important for flow measurement --- repeatability or accuracy?
By David W. Spitzer
E-Zine February 2016
Page 53 of my book Industrial Flow Measurement (ISA) states that flowmeter, “repeatability is the ability of the flowmeter to reproduce a measurement each time a set of conditions is repeated. It is not implied that the indicated flow is correct, but rather that the indication is the same each time.”
Page 56 states that the, “accuracy of a flowmeter is its ability to produce an output that corresponds to its characteristic curve.” In other words, flowmeter accuracy is based on the ability of the flowmeter to measure correctly.
If a flowmeter is not repeatable, it cannot be accurate. For example, if a flowmeter randomly measures high and low by (say) 10 percent, how can its accuracy be (say) 1 percent? If a flowmeter is accurate, it must be repeatable. For example, if a flowmeter is accurate within (say) 1 percent, its repeatability must be better than 1 percent. On the other hand, a perfectly repeatable flowmeter can have an accuracy of (say) 10 percent.
In summary, good measurement requires both repeatability and accuracy --- but good accuracy means good repeatability.
Additional Complicating Factors
The accuracy and repeatability of flowmeters are often based on Reynolds number --- not flow as implied above.
ISSN 1538-5280
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