Guide to UV Measurement
Calibration Interval
UV is tough on most materials including the optical components used in radiometers and other UV measurement devices. Most manufacturers work to achieve a ‘balance' with the amount of UV that is enters the instrument. A sufficient amount of UV is needed to produce a stable noise free electronic signal from the detector while too much UV can change the optical transmission characteristics of the components used.
Instruments are subjected to the process environment and UV systems in which they are used. Some instruments live their lives in a protective case and come out only weekly in a clean room with relatively low intensity sources. Others instruments live outside their protective case and are used hourly on a multiple-lamp high-intensity production line that has dust, dirt, abrasives and excess coatings present under the UV source. Occasionally radiometers and instruments get stuck in equipment or are even mishandled or dropped.
The above changes can cause a radiometer's reading to drift from the original values. Readings taken a few days apart may concur while the readings taken a few months apart may differ - especially if the instrument was used in a tough environment and/or mishandled. This inconsistency can lead to “unexplainable” cure failure.
Radiometers and other instruments employed in industrial environments, and particularly those used with intense UV sources, need to be recalibrated on a regular basis. Calibration is a process that adjusts for the small changes in the optics and possibly electronics that impact the performance of the instrument.
Instrument manufacturers usually suggest a time interval for calibration but in reality have no way of knowing how intense, how frequent or what type of environmental conditions the instrument will encounter. More frequent calibrations may be in order if your production area resembles the high intensity, frequent measurement, and dirty environment described above.
Most manufacturers will provide a report that lists the ‘as received' intake data on your instrument when it was sent back for calibration. Use the information to decide the best calibration interval for your products and adjust your internal procedures to reflect this.
If your instrument has been stable for several calibration cycles you may be able to go longer between calibrations. If however your radiometer gets dropped or stuck in the process, it is a good idea to send you unit back from service sooner than the expiration date on the label.