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Thread: What is a good anemometer?
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30th June 2018, 07:16 PM #1GOLD MEMBER
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What is a good anemometer?
Looking at setting up my shed with 6" ducting and wanting to upgrade the air intakes on the machines, so would be requiring one of them.
Is this a good anemomter to get? By that I mean value for money, price wise etc.
https://www.ebay.com.au/itm/LCD-Disp...item25f96709ef
It's the first one I found on Ebay that had a probe rather than a fan.
Thanks
KrynTo grow old is mandatory, growing up is optional.
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30th June 2018 07:16 PM # ADSGoogle Adsense Advertisement
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30th June 2018, 08:06 PM #2.
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Firstly you are right to choose an anemometer which does not use a propellor.
The next thing you need to know is what speed can it measure.
Most of the probe type anemometers are only good for up to 20m/s.
In a 6" duct this means you are limited to under 1000 cfm.
Its actually more complicated that this because at 1000 CFM the air flow in the middle of a 6" pipe will be well over 20m/s and at the sides it will be under 20m/s
Because you can measure no more than 20 m/s you will be limited in informed decision making.
At 1250 CFM the air in the middle of a 6" duct can be moving >40 m/s and I have yet to see a hot wire or thermistor type anemometer that goes over 30 m/s.
To do this you will need a pitot type anemometer which cost more than the the other probe types.
You can get around this using a TEST DUCT that is larger in area than a 6" duct and attach that to the 6" ducting.
I assume you have read this ?
DRAFT: FAQ - Dust Extraction (Practical Aspects)
Some time ago Lappa put me onto the TESTO anemometer which connect by bluetooth to a mobil phone. These are very useful because they can log the airflow into a file, and that is important because airflow readings are rarely steady and jump around like a frog in a sock so if you want to measure small differences there's no avoiding collecting a string of results and performing stats (you really wanted to hear that didn't you ). The TESTO units cost about 50% more than teh unit you link to but they save a lot of time and having a basic calibration certificate will produce trustworthy numbers.
Air flow calibration measurements
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30th June 2018, 08:57 PM #3Woodworking mechanic
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I still use my Testo unit. They have changed the app. which is not quite as intuitive as it was but once you get your head around it, it has the same tests and file format.
I highly recommend it even though it is more expensive.
Following on from a recent discussion is the Shed forum, the positioning of the probe at the recommended points is critical for accurate results.
i put them through an Excel spread sheet set up using Standard Deviation calculations to get an accurate average.
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1st July 2018, 02:13 AM #4GOLD MEMBER
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https://www.testoaus.com.au/testo-40...ire-anemometer
The one the boys are talking about. It measures to 30 m/s and is about $135 here in Canada, so pretty close to what you pay. The one you linked goes to 30 m/s.
Found this real quick on Aliexpress. It goes to 30 m/s
https://www.aliexpress.com/item/2017...ceBeautifyAB=0
Found more that can read 40 m/s but are 3 or more times as much. The ones in the $100 range all seem to max at 30 m/s
Pete
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1st July 2018, 08:42 AM #5.
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The website and even the calibration certificate says the Testo 405i measures to 30 m/s but the one I have doesn't - it has a max of 20 m/s.
IMG_3193p.jpg
Maybe they fixed this but there are no new models out.
The calibration certificate is only a 1 point calibration point certificate - mine is at 8 m/s. Compare that to my other analog meters some of which have a 10 point curve.
Against my other meters the Testo seems to measure too low. but it is with spec +/-10%
Calibration above 20 m/s is difficult hence rare.
BTW The flow rate (cubic metres / unit time) capabilities of these meters is useless for ducting at high speeds such as found in DC systems.
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5th July 2018, 09:33 PM #6Woodworking mechanic
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Are you stating that the Testo is useless when it comes to measuring flow rates in dust control ducting?
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5th July 2018, 10:11 PM #7.
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No - I'm saying the built in flow rate calculator whereby you enter the duct area and it uses a singe air speed measurement to calculate a flow rate is useless for high flow rates in small ducting. It works fine for large area ducting and slower air speeds.
There is also the limitation of air speeds.
1250 cfm in a 6" duct can produce as much as 42m/s air flow in the middle section of the duct - the Testo cannot measure this directly.
However if a larger diameter "test duct" is used that reduces the air speeds to the levels that the Testo can measure then it is a very useful meter.
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14th July 2018, 07:37 AM #8
I was ready to buy the Testo 425 Hot Wire Anemometer until I realized it is not suitable for the velocities in DC systems. The Testo line appears to be better suited for HVAC systems.
Since I was willing to drill small sample holes in my DC ducting, I bought the Dwyer 477AV-2 digital manometer and the 166-6 pitot tube. This combination is good for up to 128.7 meters per second of air velocity. When using the 166-6 pitot tube and entering the duct shape and size, the 477AV-2 also calculates the volume of air in CFM, m3/h, and m3/s.
My main ducting is 120mm due to routing limitations. The small shop means I have lots of wide 90-degree bends and 45-degree taps for the blast gates. Almost all of the blast gates then reduce down to 100mm ducting for connection to the equipment. Only my table saw and SCMS will keep the 120mm ducting.
I have a 2-meter section of 110mm storm and drain pipe that I will connect to the blast gate being tested with a short section of 120mm flex tubing. The pitot tube is about two thirds the length of the pipe away from the end. The long piece of S&D pipe helps ensure a smoother column of air moving past the pitot tube. As soon as I wire in the digital ammeter to my power distribution box to measure the load on the blower motor, I'll start gathering data.
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14th July 2018, 10:40 AM #9.
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The volume flow rates it calculates from a single point measurement will still be incorrect by up to 40% maybe are because you are only using 120 mm ducting. The air flow in small ducting will be highly turbulent ie vary in time and space especially if a measurement is made anywhere near a junction or bend or gate. - a series of repeated measurements radially across the duct will have to still have to be performed to determine the flow speeds and then an integrative calculation performed outside the meter.
This is why it is far more accurate to measure flows at low speeds using a long large diameter test duct attached temporarily to ducting rather than inside your real ducting. Testing inside real ducting leads to errors in measurement which can create the wrong ideas about flow in ducting systems which often drives operators into making wrong choices about which is better or worse or not at all.
Read the section on how to measure air speeds in the sticky on practical aspects of dust at the top of this forum for how to use a test duct.
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