Tech Challenge: Take the Challenge, See if You’re Right

July 28, 2011

Determining Flow Rate at Various Points on a Golf Course

A groundskeeper at a large golf course needs to measure the flow rate in the watering system at more than 30 different points throughout the course. With several miles of pipe, the diameters vary from 2 to 4 inches. The groundskeeper also indicated they want to monitor the flow continuously for 10 minutes at each point of measurement. They have a budget of less than $10,000. Which flowmeter and process would be ideal for this application?

A: Install spring-loaded flowmeters at each point around the course. Take readings every 15 seconds and record them in a notebook.

B:  Install tee-fittings with paddle wheel sensors at each monitor point, and carry a battery powered meter around the course. Take readings every 15 seconds and record in a notebook. 

C:  Use a Handheld Doppler Flowmeter and take readings every 15 seconds and record them in a notebook.

D:  Use a Portable Transit-Time Flowmeter and program the datalogger’s sample rate for one reading per second.

Check to see if you are right.


Using Your Nose

November 13, 2009

Written by:  Ben Wilbert, Product Manager, Cole-Parmer
While most scientists who study human brain evolution tend to regard something people do very well, such as language, Dr. Tyler Lorig, Ph.D. at Washington & Lee University studies one of the least understood senses and something people tend not to do so well: smell. With an interest in brain evolution and a background in EEG analysis, he studies the olfactory (a.k.a. sense of smell) system in his lab, specifically how the brain responds to an odor. Often a neglected and under-served field of science, and past research often fraught with loose control methods, Dr. Lorig decided to develop his own olfactometer. Since an olfactometer isn’t exactly the type of device you’d find on the shelf of the hardware store—or even in a specialty catalog—Dr. Lorig built his olfactometer by using many quality products from the Cole-Parmer catalog, starting with solenoid valves. The one he devised proved to be much less expensive than one valued at $100,000 on the market, yet served all the needs of his research.

One of the challenges to studying the sense of smell is being able to appropriately regulate the amount of the stimulus. It’s difficult to determine how much of an odor you’ve delivered to a test subject. While you may try and “dose” the amount of smell, there are many factors affecting the distribution of airborne molecules that provide an odor. In studying the body’s other natural senses, it’s comparatively easy to gauge precisely how much of a stimulus is applied to a subject. Light, sound, electricity, and even flavors—although taste is a field of study filled with ambiguity itself—can be regulated to keep tight controls over a scientific test. But in testing the olfactory response, even the weight of the molecule, for instance, will affect how fast it disperses, and hence sensed by someone. Lighter molecules move quicker, so if you’ve decided to expose the test subject to five seconds of a particular odor, you will get a different result than a heavier molecule that only gets a fraction of the activity in the air within the same time frame. This means lightweight molecules will invade the nose, migrate through the mucous membrane at the top of the nasal cavity, and be sensed more so than heavier molecules. To top it all off, there is even remarkable inter-subject variability, whereby one person may sense an odor sooner or later than another person.

To minimize the effects of the inherent differences in the physical nature of odors and test subjects themselves, the equipment used has to be of such design and quality that the experiment is not compromised. All parts of Dr. Lorig’s olfactometer that could contaminate smells are high purity, hence minimizing any residual odor that would affect the experiment results. Lorig admits to first coming to Cole-Parmer while looking for some high-quality solenoid valves. He sought PTFE (wetted parts) valves because of PTFEs quality to stay clean, and not absorb errant odors. In his paper “A computer-controlled olfactometer for fMRI and electrophysiological studies of olfaction”, originally published in Behavior Research Methods, Instruments, and Computers, Lorig describes the design for an inexpensive and reliable olfactometer that he pieced together and constructed from off-the-shelf chromatography parts that required little modification. Since he would be using the olfactometer near an fMRI, the olfactometer had to obviously be free of ferrous metals, which will wreak havoc near the magnet. Overall, the instrument needed essentially seven features: (1) computer control; (2) effective delivery of a variety of odors, in series or randomly; (3) production of an odor stimulus of selectable and reliable duration in a constant airstream, without any additional type of ancillary stimulation (e.g., tactile, auditory); (4) resistance to contamination; (5) durability; (6) ease of operation, refilling, and cleaning; and (7) low cost (Lorig et al. 1999).

Following the drawing above, air from a compressor is passed through a charcoal filter to remove odors and then through particulate filters to prevent charcoal dust from being administered to test subject. After passing through the particulate filters the flow is divided and metered through variable-area flowmeters. One of the lines is always open and provides a constant low-volume air stream. The other flowmeter provides the air that will be passed over the odors. This stream is also divided and passed to two solenoid valves. Valve A is a single valve that is normally open. The other valve is a multi-port valve that can have from 1 to 6 individual normally closed solenoid valves (B1-6). To send an odor to a subject, the computer turns on valve A (stopping airflow in that line) and turns on valve Bn commencing airflow in that line. The syringe filter connected to line Bn contains odor, and the air now passes over the filter and through the manifold to the subject. Turning the valve off stops airflow over the filter paper and stops the blockage cause by actuating valve A. To avoid any increases in air flow, one non-odorized line is stopped during odor stimulation making the net change in air zero. Because the switching in the valves lead to very brief airflow changes (around 20 milliseconds) the constant flow line acts as a buffer for the airflow change, thereby reducing any extraneous sensory stimulation to the test subject.

“Some of the research done shows we are exquisitely sensitive to smells, contrary to our expectation.” states Lorig.

In relatively normal test subjects, Lorig finds people have measurable brain activity induced by odors, even when the test subject reports not smelling anything! Even when more than one chemical is blindly switched—neither reported as smelled—they render different brain responses. While brain patterns related to particular smells may evoke similar and predictable brain responses, Lorig is careful not to jump too far in his conclusions, for example, they will not indicate emotions such as fear or joy.

Lorig notes that when it comes to the extreme smells, people tend to agree across cultural boundaries as to what smells bad and what smells good. On the bad end of the spectrum, odors such as feces and cadavers evoke similar negative responses from people, and on the pleasant end, vanilla ranks universally high as a positive response from people. But in the vast midsection of the odor continuum, there is a wide variance regarding what is pleasant versus not-so-pleasant odors. Other interests include why some people find certain odors pleasant or at least tolerable, while others find them absolutely repugnant.

“Since I’ve talked to so many people about smell, they will sort of confess, ‘Oh, I really like skunk smell.’ ”

While much of the current olfaction study takes place in a research setting, Lorig states he would like to see olfaction analysis become simplified . There’s now understanding of the connection between olfaction and certain health problems. Current research examines the relationship between olfaction and maladies such as Parkinson’s Disease, Huntington’s Disease, Korsakoff’s Syndrome, Schizophrenia, Depression, and Alzheimer’s Disease (AD). Recent evidence suggests that areas in the central nervous system processing olfactory information are affected at the early stages of AD, even before the onset of cognitive decline, and that olfactory dysfunction might be an early indicator of AD (Murphy, 1999). The smell threshold is much higher for those who suffer from AD.

Aside from aiding pathological diagnosis, Lorig’s current and future toils include researching how the brain is organized, the pathways the brain uses to process odors, and the many relationships between smelling and the other senses. Cole-Parmer continues to provide scientific instruments used by these professionals to support the overall advancement of science. We thank Dr. Lorig for his time and efforts in providing valuable feedback about our products and wish him well in his future endeavors.

References
Lorig TS, Elmes DG, Zald DH, Pardo JV (1999) A computer-controlled olfactomenter for fMRI and electrophysiological studies of olfaction. Behav Res Methods Instrum Comput 31: 370-375.

Murphy, C., 1999. Loss of olfactory function in dementing disease. Physiol. Behav. 66 (2), 177-182.

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Less Is More: Buying Inexpensive Flowmeters

November 11, 2009

Accuracy, repeatability, reliability, installation ease, and price – these are some of the basic criteria on which flowmeters are selected. And while it may be preferred to have the best flowmeter that money can buy, it is not always necessary to buy that most expensive one. For example, you may not need the most accurate flowmeter available, whereas, the same is not necessarily true of repeatability – especially if you use your flowmeter to control a process or a batching operation. But even in such a case, you may not need to buy the most repeatable flowmeter available.

Reliability varies as well from flowmeter to flowmeter, between different flowmeter technologies and even within similar technologies. In fact, reliability may vary within a single manufacturer’s product line. And face it, reliability costs money: The more reliable the flowmeter is expected to be, the more costly its purchase price is anticipated to be.

In some cases, you may be able to purchase several “less reliable” flowmeters for the same price that you would pay for a single unit of the most reliable flowmeter. And sometimes, but not always, installation ease of a flowmeter costs more. Keep in mind that installation ease is not correlated with accuracy or reliability; sometimes you have to give up accuracy or even reliability to get easy installation.

Applied Cost Analysis Price is a fairly good indicator of a flowmeter’s limitations. But that doesn’t mean that it is a good indicator of “how good” the flowmeter actually is. “How good” is really a function of how well matched the flowmeter is for your application.

As applications get more difficult, the number of flowmeters that work will decrease and the price of the flowmeter that can perform well in that application will increase. Conversely, as applications become easier, the number of flowmeters that can perform well will increase, whereas the price of those flowmeters will drop. This is an important point. Many flowmeter users immediately purchase the kind of flowmeter they are familiar with or the kind they believe to be the most accurate or reliable without actually thinking through the application. In many cases, you can save time and money by evaluating the application first and then selecting the flowmeter based on what will actually fit the application. Indeed, you can often plan the application so that you can use an inexpensive flowmeter if you start early enough in the design stage.

For example, if you have a conductive liquid at ambient temperature and moderate pressure and you have provided sufficient straight run both up– and downstream from the meter and you have sized the meter to produce approximately 60 percent of signal at the application’s average flow rate, then you can use any flowmeter you want with the appropriate materials of construction. Or if you have a gas flow at reasonable temperature and pressure and you’ve provided an adequate piping configuration, then you are free to use many different types of gas-flow devices.

In another example, if you are simply totalizing flow over a daily, weekly or monthly period, a variety of flowmeters will be adequate. The longer the baseline over which you are totalizing, the more accurate your total will be, regardless of what flowmeter you use. The flow totals from sewer-flow data loggers that take data every five minutes or so are known to be as good as continuous measurements totalized in the same location.

As a final example, if you are controlling a metering pump or other chemical feed device, you need only have a flowmeter in which the accuracy is better than that of the chemical feed device itself. It isn’t necessary to use a terrifically accurate flowmeter with a chlorine gas feeder, which is accurate to +/-4 percent of full scale.

So how do you figure out if you can use an inexpensive flowmeter? Simply study your application. If the application parameters can be done with the inexpensive flowmeter to the desired accuracy, repeatability, reliability and cost effectiveness, then use the cheapest flowmeter you can find.

If you really want to make sure that you are getting the least expensive flowmeter that will work adequately in your application, reverse the field. Start by setting a cost target for the flowmeter. Set a low one. Examine all the flowmeters under that cost target against your application. If none fits, raise the cost target and redo from the start. Keep raising the cost target bar slightly; doing so will permit you to work with, as well as evaluate, different flowmeter types and those more costly flowmeters that were over the bar previously. Eventually you’ll hit a flowmeter that will perform adequately. Buy that one.

View our complete selection of Flow meters

About the Author Walt Boyes is a senior member of ISA and current vice president of ISA’s Publications Department. He is a writer and consultant who has delivered numerous technical papers. He has more than 25 years in the practice of flow control.


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