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OTHER TEST GEAR UPGRADES
Long time readers of SPCR know that we have a broad range of test gear, not only for audio analysis but also thermal and fan testing. The precision and suitability of some of this gear is not beyond reproach. A decision was made to go ahead and add a few more items for a wholesale improvement to all our test processes.
Kanomax 6803 Anemometer
The SPCR lab is already equipped with with two anemometers for testing fans. The first is an inexpensive vane anemometer which proved imprecise at lower airflow levels, and subject to strong variations depending on the twisting. cyclonic action of fan airflow. The second anemometer is a more serious tool, an Extech Model 407123 hot wire device described in detail on page 6 of "A New Way of Testing Fan Airflow". While the Extech is a significant advance from the first vane anemometer, its 3% accuracy is assured only to 40 ft/min velocity, with a resolution of 10 ft/min.
Part of the problem is that we're seeking precision and accuracy down to very low airflow, but anemometers are generally designed for checking weather conditions or for heating, ventilation and airconditioning (HVAC). In both applications, the airflows of concern are many times higher than that of slow spinning fans for PC cooling.
The Kanomax 6803 is another vane anemometer, but its precision and resolution is far better than either of the other ones. It is described as a tool not only for HVAC but also for "Laboratory Control, Cleanrooms, IAQ Investigation, Industrial Hygiene and Quality Control." The specified accuracy is within 1%, and the resolution is 1 ft/min. Like the ACO Pacific microphone, this $650 tool came packaged as a kit in a tough carry case. The most impressive part of the system is the Pacer 275 vane probe, formed from machined aluminum or steel. Its bearings have such low friction that just walking while holding it is enough to get the vane blades spinning, and for the meter to produce readings. The vanes also seem essentially impervious to variations in reading due to the cyclonic action of fan airflow, but this has to be confirmed with more extensive testing.
Kanomax 6803 vane anemometer kit.
The 2.75" diameter vane probe with short handle, attached via cable to the anemometer.
The low friction of the calibrated Pacer 275 vane probe is astonishing.
FAN RPM MEASUREMENTS
A laser Neiko Tools USA digital tachometer has been used to measure fan RPM during testing. It works by pulsing a tight beam of light against the rotating element. A piece of reflective tape is affixed to one of the blades, and the tachometer measures the rate at which the light beam is reflected back. This works fine as we have access to the blades, but there's been no way to confirm the measured RPM. The accuracy is claimed to be 0.05%, but this is a claim I'd take with a LOT of salt.
Inexpensive laser tachometer with reflective tape: 0.05% accuracy?!
Another RPM measuring device was needed to check the results from the laser tachometer. A strobe with calibrated pulse rate seemed like a good option as it requires no contact with the fan and not even a piece of reflective tape, which is useful in some cases where the blades are not accessible. The item chosen was another from the eBay store, Easy Life Product. This $120 AC powered handheld device is claimed to have the following key specs: Resolution : 0.1 FPM (50 - 999.9 FPM), 1 FPM (over 1000 FPM); Accuracy : ± (0.05%n + 1d). Again, the claim is difficult to accept.
Handheld strobe as backup for laser tachometer.
The flash rate is displayed.
Here's how the strobe is used to measure fan speed: The strobe is turned on and the light pointed at the spinning fan blades. Sometimes it helps to dim the ambient light. The speed knobs are adjusted until the fan blades appear stationary. This can occur when the flashing rate is at any number of multiples (or fractions) of the actual fan RPM. In other words, when 1043 RPM is displayed and the fan blades appear stationary, the actual fan speed could be 522, 1043 or 2086 RPM. Affixing a piece of reflective tape on a blade makes it more positive: The tape appears stationary only when the strobe flash rate matches the fan RPM.
So far, testing comparisons between the two fan RPM measurement devices shows good correlation; often dead on, and usually within 5%. Which is the more accurate is difficult to gauge, but the alternative measurement tools are reassuring.
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FUNDING THE PROJECT
In April 2008, I asked the SPCR community for help to fund this project. Corporate sponsors were also contacted. Both readers and corporate sponsors responded generously, with cash donations from readers, and product gifts, randomly awarded to the individual donators, from the corporate sponsors. It was a successful fundraiser; some $11,000 was raised for the project in about one month. The progress of the fundraiser was documented as it unfolded in this lengthy forum thread.
There are too many individual contributors to name them all (some 300), and most want to keep their privacy. To all of you: My heartfelt thanks! Without you, this project would not have gone forward.
The corporate sponsors also deserve recognition, thanks and praise for their part in offering giveaway prizes for individual contributors. Their support is much appreciated by everyone involved with SPCR!
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Other SPCR articles of related interest:
An Anechoic Chamber for SPCR
Audio Recording Methods Revised
SPCR's Test / Sound Lab: A Short Tour
SPCR's Fan Testing Methodology
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Discuss this article in the SPCR forums.
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