Windspeed Limited (Vector Instruments) - Manufacturers of Quality High-Precision Anemometers, Windvanes and Weather Sensors for 50+ years

Windspeed Limited

Anemometer, Windvane and Air Temperature sensors

Saturday, July 27 2024

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Celebrating more than 50 years manufacturing & servicing High Quality Vector Instruments Anemometers and Windvanes at Windspeed Ltd

What is the difference between "M" and "K" type instruments (e.g. A100LM and A100LK) ? Do I have to use a "K" instrument to measure the wind speed in knots and a "M" instrument to measure in m/s ? What is the A100R/K variant and why/when should it be used? What is the "K" in A100R/K for?
Answers: What is the difference between "M" and "K" type instruments (e.g. A100LM and A100LK) ? - The "M" and "K" just refer to the basic "scaling" in the case of our "opto electronic" instruments (A100LK, A100LM, A100M, A100K) - The "K" types are configured to give nominally 10Hz per Knot and "M" types are configured to give nominally 10Hz per m/s (metres per second). This just means that the "K" types give around twice as many pulses out (about twice the frequency) vs the "M" types at the same windspeed. Do I have to use a "K" instrument to measure the speed in knots and a "M" instrument to measure in m/s ? No. Your data logger simply has to measure the frequency given out by the instrument and use an appropriate scale factor (and offset if desired) to get the results into whatever "units" you prefer, be they Knots, m/s, KmH, MPH, ft/sec or whatever. "Historically" when measuring/display equipment was a lot less sophisticated, it was convenient to have an output frequency signal that could display on a standard frequency meter and be read directly as windspeed by just moving the decimal point, with modern dataloggers that can usually apply any scale factor you like, this is no longer as important. Provided that the datalogger can cope with the higher frequency signal from a "K" instrument (rememeber, the optoelectronic "K" instruments give about twice the frequency at the same wind speed compared to the "M" instruments), then the "K" type should be used because it gives better measurement resolution (more pulses per rotor revolution). You can of course scale/offset the signal from a "K" instrument to give results in m/s rather than knots (in fact, if the instrument has a MEASNET calibration, then the scale/offset factors on the MEASNET calibration certificate will give results in m/s units). What is the A100R/K variant and why/when should it be used? The A100R family of instruments requires no power supply (unlike the other "optoelectronic" instruments we make), and they output a much lower frequency (only one pulse per revolution instead of 13 or 25). Some dataloggers don't have sensor power available and/or can only measure low frequencies, e.g. upto 80 or 100Hz or so, which means that our "optoelectronic" instruments are not suitable. This is when the A100R/K is the correct choice if you have a "first class" application. The "standard A100R", however, has a rotor (R30/S) which is dimensionally somewhat different to the rotors used on all of our "first class" instruments (A100L2, A100LM, A100LK etc) and the R30/S has not been verified for "first class" applications. When the A100R/K is ordered, this problem is eliminated because the anemometer has the same body shape, bearings and same R30/K family rotor as our optoelectronic "first class" instruments and will perform similarly. The only difference is that a reed/magnet system (as per the "standard A100R") is used to sense/measure the rotation of the rotor instead of an optoelectronic system. The classification tests for our optoelectronic "first class" instruments used a rotor of the R30/K (or R30/M) "family" and these other rotors will fit the A100R, so we recommend that a R30/K "family" rotor be used with the A100R anemometer "body" when it is intended for "first class" applications to ensure the best performance (i.e. best "cosine response" etc) when the "optoelectronic" instruments cannot be used. What is the "K" in A100R/K for? The "/K" in A100R/K simply means that the product is shipped with an R30/K rotor instead of the R30/S rotor shipped with the "standard" A100R. In this case, the "K" does not refer to the "scaling" of the output signal "being in knots", although the different rotor means that the nominal calibration of the A100R/K is slightly different to that of the "standard" A100R.
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Windspeed Limited (trading as Vector Instruments),
113 Marsh Road, RHYL, North Wales, LL18 2AB, United Kingdom
Tel: +44 (0) 1745 350700
Email: sales@windspeed.co.uk