Thread: DE Measurements

What model Supervac is it?

Most of the Supervacs on the T-Quip website are showing 2210 mm of static pressure which is pretty close to what you are seeing.

This is mine

http://www.shopvac.com.au/images/597...per20LPoly.pdf

IMG_0505.jpgMy new toy

Even comes with a calibration Cert

Looks nice.

I'm trying to make sense of the calibration data - I suspect it is calibrated to 30 m/s but it only ISO certified up to 10 m/s?

Accuracy is +/- 0.3 mS +5% of measure value up to 15 m/s and doesn't say what it is above that speed.
At 15 m/s that +/- ~1.05 m/s .
The Kurz meter I have has an accuracy of 0.65 m/s at 15 m/s, while the TSI has an accuracy of 0.3 m/s at 15 m/s.

Anyway, for relative measurements this doesn't matter as the calibration and accuracy is not that relevant for relative measurements where flow variability will be the limiting factor.

I'll be interested to hear how it goes.

The thing with calibration certificates is that they only mean something if the lab is competent and ethical. The only way to be confident of this is if the lab that did the cal has been Accredited to ISO17025 by an independent body like NATA or has an accreditation recognised under the international mutual recognition agreement or ILAC. Otherwise the report could be worth no more than the paper it's printed on. In order for the calibration to mean anything it needs to be traceable to a primary reference standard, be conducted by proficient people to a technically correct and audited procedure and the results be reported to a known level of uncertainty.

Does the calibration report say anything about NATA, ISO17025 or NIST or ILAC ? Doesn't mean the meter isn't good or that the calibration wasn't done correctly, but it reduces the level of confidence.

Wow. A lot of negativity regarding a fine piece of German Instrumentation

No mention of any of the above but It meets DIN EN ISO 9001:2008 certified quality assurance system and the German Federal Physical and Technical Institution (PTB) Standards in Calibration Laboratories accredited by the German Calibration Service (DKD).

BTW their test equipment is widely used in the HVAC industry which is where I got the lead from.

Originally Posted by Lappa

Wow. A lot of negativity regarding a fine piece of German Instrumentation

Two responses = "A Lot" ???

Okay, maybe an exaggeration, but I'm surprised than the two responses seem to question the validity of the calibration certificate and therefore the instrument itself.
It's not as though my new meter is a fleabay cheapey bought via Hong Kong or China. It's a unit made by a German company and purchased from their company branch in Melbourne and the certification process meets the standards required by industry. This was all researched before purchase, as I do for all equipment I purchase, especially for data acquisition. If you look at their website, they manufacture and supply test equipment to many areas of industry, including HVAC.
The Bluetooth aspect is one which a number of manufacturers are now following to reduce instrument costs and allow rapid collection of data without having to write readings down. One aspect I liked about this unit is I can snap a series of readings in the designated grid pattern then export the data as graph, excel file or PDF.

For DomAU - yes, the PTB test under ISO17025

http://www.ptb.de/cms/fileadmin/inte...ation_2015.pdf


Enough said - on with the measurements.

Hi Lappa,

Sorry, it wasn't my intent to criticize your new meter. I just saw talk of calibration certificates and wanted to pass on some general info. A lot of people think that just because an item has a cal. Cert. It must be accurate. In your case if the cal is conducted by PTB then that's really good and is recognised under the MRA. A good calibration certificate will also report the least uncertainty of measurement that the lab is accredited to as well as the uncertainty of the equipment calibrated, which will be greater given the additional uncertainty of the back to back comparison as well as the random error / repeatability component (which can be large for some equipment).

Of course, the uncertainty of the test equipment (your anemometer in this case) will be just one part of the total uncertainty of your measurement. This will include all sorts of Systematic and Random errors that would need to be considered. But I digress and for our purposes let's not worry about it haha. Unless you want to start testing professionally.

Originally Posted by DomAU

Of course, the uncertainty of the test equipment (your anemometer in this case) will be just one part of the total uncertainty of your measurement. This will include all sorts of Systematic and Random errors that would need to be considered. But I digress and for our purposes let's not worry about it haha. Unless you want to start testing professionally.

We do test professionally when testing HVAC systems and provided well proven protocols are followed, systematic and random errors are minimised. There is no uncertainty with the equipment we currently use. Indeed there should be no uncertainty when one buys first class equipment from a reputable company with appropriate certification, but I understand that using new devices using new technology does change the playing field somewhat. We will be buying and trialling more of the Testo Bluetooth HVAC gear to see how it stacks up against the standard equipment we use now as it's compact size and portability will be a bonus.

Originally Posted by Lappa

Okay, maybe an exaggeration, but I'm surprised than the two responses seem to question the validity of the calibration certificate and therefore the instrument itself.
It's not as though my new meter is a fleabay cheapey bought via Hong Kong or China. It's a unit made by a German company and purchased from their company branch in Melbourne and the certification process meets the standards required by industry. .

I can't see where I criticised the calibration or the instrument. I thought I was quite positive about the instrument and all I said I wanted to "understand" the calibration.
This was purely from my own curiosity as I am part of an international panel that deals with chemical standards, and accuracy and reproducibility was part of my day job for 40 years.
Having worked with quite a few Germans on these standard panels, one thing I have noticed is that Germans are inherently conservative so it does not surprise me that they place a conservative uncertainty on their calibration processes. I suspect that the specific instrument accuracy could be better than the quoted values, do they actually provide the calibration measurements?

My Krauz unit just provides a certificate saying that the unit has been calibrated against a NIST calibrated instrument - secondary calibration.
The TSI certificate actually provides the calibration values showing differences to the measured standard , with the differences between the two measurements being much smaller than the final statement of accuracy.
Expanding the final accuracy figures is standard procedure because they need to take into account the variability between all the instruments they make/sell.

After thinking about it for a while I think I might know why the calibration tops out at 15 m/s, my guess is because those ISO standards are for HVAC and HVAC rarely requires calibrated speeds above 15 m/s.
There is a bit of a difference between HVAC and dust extraction. HVAC is generally low speed laminar flow, large ducts, where single air speed measurement is all that is needed to measure flows. When I started measuring air speeds in labs I also thought the HVAC approach would suffice and it took me some time to appreciate that wood dust is quite a different environment that few HVAC people would even know about.
This is probably why the ANZS test for dust extractor air flows is wrong because it has been done using a HVAC approach, single measurement in the middle of an air stream which is just not good enough by as much as a factor of two. So while some HVAC instruments are useful for DE flows they have to take into account these issues.

FWIW I note the instrument is made in China, probably by a Testo subsidiary.
This is not a criticism, just reporting what I saw on the suppliers website.

Originally Posted by Lappa

We do test professionally when testing HVAC systems and provided well proven protocols are followed, systematic and random errors are minimised. There is no uncertainty with the equipment we currently use. Indeed there should be no uncertainty when one buys first class equipment from a reputable company with appropriate certification, but I understand that using new devices using new technology does change the playing field somewhat. We will be buying and trialling more of the Testo Bluetooth HVAC gear to see how it stacks up against the standard equipment we use now as it's compact size and portability will be a bonus.

If you say there is no uncertainty then clearly you have no idea about uncertainty.
Relying on instruments and new technology to fix uncertainty is inherently unreliable.

I am reminded of the dudes in a lab who bought the $1000000 German mass spectrometer because it could measure to 0.000001% when I asked them what their external uncertainty was he quoted his internal uncertainty - in other words he didn't know the difference.

The main uncertainty in DE system measurements is usually unrelated to instrumentation uncertainty but due to the variability caused by turbulence.
Unless this is understood and allowed for then folks will go round and round in circles making meaningless changes to DE systems based on meaningless measurements

Lappa, no measurement can be 100% certain. There is a level of uncertainty associated with any measured value, whether it is reported or not. Uncertainty is usually expressed as an expanded uncertainty, usually in +- percentage terms (or measurand units) at a 95% confidence level and an associated coverage factor (k) and degrees of freedom.
For example a properly considered measurement would report a value of 20m/s, uncertainty of +-1.4m/s at 95% confidence and coverage factor k =2. This would then inform the user of the measurement on how to best treat this result and/or allow them to incorporate this measurement uncertainty into their greater uncertainty if this was to form part of a larger test/measurement. Sorry it's hard to write a good explanation on a damn phone.