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Windspeed Ltd (Vector Instruments), 113 Marsh Road, RHYL, N. Wales, LL18 2AB, United Kingdom.
Windspeed Limited
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Celebrating more than 50 years manufacturing & servicing High Quality Vector Instruments Anemometers and Windvanes at Windspeed Ltd
MEASNET Calibration Certificate Validity/Duration    
You should contact the MEASNET test house that issued the Calibration Certificate(s) in question to determine whether it is still valid.

Things that can invalidate ANY calibration are:
  • Changing/replacing the anemometer bearings
  • Changing/replacing the rotor
  • Damaging the rotor, particularly the cups and arms (even slightly), e.g. objects/debris striking the rotor/cups (such as ice falling from a structure), or knocks during installation
  • Attempting to repair a rotor, e.g. by trying to straighten bent arms, trying to remove/refit/change/tighten or adjust individual cups on a rotor
  • Installing on a different mount/adapter/pole size to that used in the calibration
  • Having Worn/Noisy bearings in the anemometer (e.g. due to ingress of dirt/dust/water)
  • Oiling/Lubricating the anemometer bearings (our anemometer bearings should be considered "lubricated for life" as they contain a precise amount of a specially selected lubricant and should not be oiled/lubricated by the user)
  • Fitting of non-standard parts (such as touching seals, different rotors, external heaters), or modifying the rotor/anemometer/cable or mount
This means that any pre-existing calibration will always be invalidated by maintenance/repair/refurbishment of an anemometer, and a re-calibration will be required.

We are often asked for general advice on validity of MEASNET calibration certificates, especially in the case of an anemometer/rotor which has been stored (not used) for a period after calibration. We have asked various experts in the "wind industry" for advice, and the guidance we received is as follows:

MEASNET calibrations are only valid for 12 months after the anemometer has been installed on a mast/tower (i.e. "installed in the field"), assuming the anemometer has been stored in "good conditions" and is installed within a "reasonable period" of the actual calibration test date.

The "12 month validity period" mentioned above is subject to the following warning:
Be aware that the max. 12 month operation (measuring) time at at the site is greatly dependent on environmental conditions like dust, aerosols, spray of salt water, icing etc.

We have been advised that stored in "good conditions" means:
Protected from physical damage/stress/handling, stored in a dry/clean environment with small temperature/humidity variations & small amounts of aerosol/dust content, and with restricted access to the storage location to prevent tampering with the anemometer/rotor (i.e. the anemometer box remains "sealed", dry and undamaged).

We have differing advice from the experts that installed within a "reasonable period" means:
upto between 6 and 12 months" depending upon actual storage conditions, with some experts suggesting maybe as long as "24 months".

Ultimately, the decision as to whether a calibration/certificate is valid is down to the end user (i.e. the user who requires the wind data) - some end users may may have a QA/Calibration policy requiring frequent calibrations which does not allow for "storage" for periods as long as 24 months.

In high-accuracy applications, we always advise that anemometers be returned to us for maintenance/overhaul and recalibration between deployments - see further guidance here.
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Windspeed Ltd (Vector Instruments)
 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
 
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