Two by Dwyer.

Earlier this year, we were honored to present our Hands-on Instrumentation Workshop to the Alaska affiliate. After the session, as we repacked our tools, we had our usual critique and brainstorming session to decide what to emphasize, de-emphasize, add, or leave out for the next go-around. We realized that we'd been neglecting one tool--the Dwyer[R] 460 Air Meter kit--and decided we should have spent more time explaining its versatility and the many things it can do. The kit has been around for well over 30 years, without much change, and can be found in virtually every maintenance engineer's desk or toolbox. Somehow, we always manage to take it along when we inspect institutions--for that "just in case" situation--but because it is so inexpensive and unobtrusive, we also have been taking it for granted. It's about time to right this oversight, and we hereby feature the Dwyer 460 Air Meter and a companion instrument: the "Wind Meter," a versatile tool for outdoor use.

The Dwyer 460 Air Meter

Weighing in at a mere 6 ounces, the No. 460 Air Meter kit is easily overlooked. It does not come in an impressive package (more on that later) and has no bells and whistles. At first blush, it looks like a cheap "give-away" from a vendor seminar. Looks, however, are deceiving: The 460 packs quite the wallop as a ventilation measuring tool and has saved the day for us on numerous occasions. This unit is a precision air velocity and static pressure indicator based on the principle of the variable-area flow meter. The heart of the kit consists of an air meter (the variable-area flow meter), and it has one moving part--a small, white plastic ball. The flow meter works by holding the ball up. Air comes in through the outer of the two top connectors, passes into the scale chamber, and enters the tapered indicating tube at the bottom. This causes the small white plastic ball to lift; the height of the ball indicates air velocity or static pressure, with their relative scales on opposite sides of the flow meter. No b atteries are required, and, for accuracy, the flow meter can be calibrated. Other components of the kit include a supply grill probe and a return grill probe, an angle connector (Pitot tube) and 14 inches of rubber tubing, a maintenance kit for cleaning the instrument after use, a slide-rule-type air velocity calculator, and an easily understandable instructions card. All this for less than $30.

Although it takes a little practice, the kit is easy to use. The instruction card gives clear directions on how to hook up the components to measure duct air velocity, supply grille velocity, return grille velocity static pressure, and, if needed, furnace draft and air filter test. Air velocity registers from 260 to 1,200 feet per minute (fpm) at low range, 1,000 to 4,000 fpm at high range. Static pressure is 0.005 inches to 0.09 inches water at low range and 0.05 inches to 1.0 inches at high range. To make high-range readings, simply cap the exposed connector with a finger. The kit gives formulae for calculating cubic feet per minute and adjusting for grille openings. Because the flow meter is not self-correcting for temperature and humidity as with an electronic thermal anemometer, you will need to know the air temperature, humidity and barometric pressure. The air velocity calculator is then used to obtain air density over a 1.00 correction factor for both velocity and static pressure. Since we always car ry a thermohygrometer or sling psychrometer with us, we have ready access to temperature and humidity readings. Any radio weather report gives us the barometric pressure.

Do not be too hasty to dismiss this product as requiring "too much effort"; it doesn't. Because the kit is so inexpensive, compact, portable, versatile, and useful, we include it as a basic tool in our carry-along inspection bag. The only drawback is the case the kit comes in-one of those semi-rigid plastic envelopes that loses its shape, cracks, and becomes "icky" with age. We would appreciate it if the nice folks at Dwyer would offer the option of purchasing a properly sized hard-sided case or rigid cloth-clad cardboard holder similar to the type made for our infrared thermometers; such an option would certainly make it easier to carry the instrument.

The Dwyer Model PWM3 Pocket Weather Meter

When we first started our practice as forensic sanitarians, we learned that supporting measurements are often as important as the actual measurements when we present findings for various environmental parameters. For instance, if we are citing the poor cooling capacity of a walk-in refrigerator, it is often as important to describe the air movement within the unit as to take its ambient temperature. The same principle applies when we are measuring the indoor air quality of workplace and institutional environments, particularly with respect to the temperature and humidity of living areas. After all, a bone-chilling, howling wind or beating sun on a blistering hot, dead-calm day will certainly affect indoor temperature and humidity. For this reason, we routinely measure external temperature, humidity, and wind speed and direction at the time we make our inspection; it builds a convincing argument in court. Until recently however, we lacked a single instrument that would do all those measurements for us.

At the beginning of the summer, we came across an ad from Dwyer extolling the virtues of the Model PWM3 Pocket Weather Meter, commonly known as their "Portable Wind Meter." This little watch-battery-operated, impeller-driven unit measures wind speed (from 0.7 to 89 miles per hour), temperature, humidity wind chill, heat stress, and dew point in less than a minute--all with the push of a single button, The readout displays knots (handy with one's fishing boat), meters per second, kilometers per hour, miles per hour, feet per minute, and Beaufort scales (from Calm to Hurricane). The level of accuracy is rather remarkable for such a small unit: within three percent of the wind speed reading or the least significant digit, whichever is greater. Temperature accuracy is within 1[degrees]C; humidity within three percent, dew point within 2[degrees]C, and heat index within three percent.

The Wind Meter weighs only 3 ounces and has a hard slip-on case to protect the sensors and impeller. Although the unit is waterproof, the manufacturer cautions against exposure in a salt environment. The impeller is replaceable, the watch battery has a 400-hour life, the unit features a 30-minute auto off, and its large liquid crystal display is easy to read. In all, we enjoy using this instrument because of its versatility and ease. It is not inexpensive at $175, but when you consider all the other tools you would need to obtain the same measurements, the Portable Wind Meter is a bargain and well worth the price. The only drawback is the instruction sheet. A poorly cropped copier copy was enclosed with the unit we purchased. The instructions were concise but barely readable, and the graphics were smudged. Operation, however, is simple enough so that you can figure out what function each push of the "mode" button displays.

For some reason, unless you have a customer ID number, access to the Dwyer Web site is restricted. You can call, however, at [phone] (sorry, no 800 number), and Dwyer will gladly send a catalog with pricing information.