Kipp & Zonen Blog

Re-calibration: a matter of good maintenance practice

[fa icon="calendar"] October 03, 2017 / by Jan-Willem Sips

Jan-Willem Sips

On evenings and weekends with beautiful weather, I tend to jump on my old-timer scooter and ride the winding roads in the neighbourhood. The scooter is from 1962, and my father used to drive it to work in the sixties. It is still rolling along due to its high build quality and my ongoing good maintenance.


You might have read that the oldest operational Kipp & Zonen pyranometer we found is located in Freiburg (Germany) and 46 years old. Like my scooter, it is still operational due to its build quality and good maintenance! You have to clean the dome, ideally at least every 2 weeks (or as soon as it gets dirty) and at the same time check the levelling and inspect the desiccant colour (and change it when required). With many of our recent instruments you don’t even need to check the desiccant, it is sealed inside.

Part of pyranometer maintenance – and luckily not part of old-timer scooter maintenance – is regular re-calibration. Under the influence of solar radiation, mostly the UV light, the sensitivity might have changed slowly over time. 

Every 2 years

As long as your pyranometer is stored safely in the dark and the desiccant changed as necessary, its sensitivity will not change. After 2 years in the field, Kipp & Zonen recommends that the instrument is sent in for re-calibration. The field pyranometer is fully serviced, the measurement readings are compared to a reference instrument and a new sensitivity is calculated. If the sensitivity change is out of the expected range (this occurs rarely) it could be that a repair is necessary; for example due to lightning damage or the pyranometer being dropped.

There is always a local calibration facility relatively nearby; Kipp & Zonen has facilities in the major solar energy regions. After re-calibration your instrument is fitted with a new label that shows the sensitivity and re-calibration date and is provided with a new printed calibration certificate that is fully traceable to the World Radiometric Reference in Davos, Switzerland. Your pyranometer is now good to go for another two years of high quality solar irradiation measurements.

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Whilst your pyranometer is being re-calibrated you can continue measuring with minimal downtime by using a replacement instrument. For our Smart SMP series models the swap is particularly easy; just set the right (Modbus®) address, disconnect the original instrument and plug in the replacement.

Local service, global quality

At our local service and calibration locations instruments are cleaned, inspected, tested and the desiccant replaced before re-calibration. This is done to factory standards and procedures. All our locations have calibration equipment identical to that used at the Kipp & Zonen headquarters in Delft, the Netherlands. They operate through the factory software, server and database and are monitored continuously, with an on-site audit every two years by head office staff. The factory carries out more difficult or unusual repairs that require specialised equipment.

Over ten thousand calibrations per year

We sometimes see pyranometers calibrated at other laboratories, which have significantly different sensitivities when compared to using our facilities. Since we perform over 10,000 calibrations of pyranometers annually worldwide, we can conclude that the quality of calibrations in the market is not always perfect. All the information and history of an instrument’s calibration by an official Kipp & Zonen facility is logged in our central database and quality checked. Sensitivity changes can be monitored and Kipp & Zonen pyranometers are proven to be very stable with time.

Our Smart instruments contain information on the last 10 re-calibrations, with the date and sensitivity. Kipp & Zonen calibration centres are the only locations where the SMP internal data can be updated after re-calibration.

Naturally, we at Kipp & Zonen recommend Kipp & Zonen calibrations. Why would you go anywhere else!

Download the infographic on the calibration of pyranometers to learn what, why, how, when and where about calibrations.

Calibration of pyranometers - LP - Infographic.png


Topics: Calibration, maintenance

Jan-Willem Sips

by Jan-Willem Sips

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