Listed below are key factors when purchasing a UV light meter.
- 1. Is it based upon the NIST Standards?
Having your meter based upon the NIST standard is absolutely necessary when purchasing a UV meter. Using the NIST Standards creates accuracy and repeatability. When you measure the light output, the number you receive can be either a relative number or an exact number. Measuring a relative number can create problems. There are a number of manufacturers that use “in-house standards.” This means an arbitrary number was used to establish the measurement and only that manufacturer uses that standard. Many of the UV meters from Asia and Europe seem to used a relative measurement.
Whereas, if the establish number is based upon NIST Standards you know it is exact to a scientific standard and accepted world wide. And, when you have your meter calibrated again, the same exact number is used. A relative number can shift depending upon the electronics and manufacturing design. Also, another downside, you must send your UV light meter to that manufacturer (turnaround time could be a problem).
- 2. Is the UV light meter linear?
Is the unit linear over a wide range of intensities levels. As the intensity levels of the source output increases, does the percent differences stay constant or does the percentage difference change when increasing the source output. Non-linearity can occur because of the electronic components used in the unit. A well design unit should, percentage wise, remain the same when measuring lower intensities compared to higher intensities.
- 3. Are the measuring probes interchangeable with the basic unit?
This tells us something about the unit. When you send in your unit for calibration (recommend on a yearly basis), does the calibration occur in the basic unit or in the measuring probe? We have seen significant calibration problems with units that require the unit’s electronics to be adjusted when calibrating. The electronics in the unit simply do not have enough adjustment capability for the deterioration of the glass stack used in the measuring probe.
- 4. Are the measuring probes interchangeable?
This key factor is also related to factor 3. How flexible is this UV light meter? Let say, you are currently measuring your application at 405nm. Then, new chemistry is offered allowing you better process benefits at 385nm or 280nm. Do you have to buy a new complete unit or just a new measuring probe? Again, the cost benefit of purchasing a new measuring probe or a new complete unit is a factor.
- 5. Calibration turnaround time.
When you purchase a UV light meter and need to have the unit calibrated several concerns come up. Where do I send the unit and how long will it take to get the unit back? If you have a meter that is based upon a relative number, then it must be sent to that manufacturer wherever that manufacturers is located. If the meter is based up the NIST standard then any good calibration vendor located wherever.
The other major concern should be the turnaround time. Once your unit is received, how long will it take to get it back? Also consider, will a new calibration certificate be issued with the meter? Will you have to pay for the new certificate or is it part of the service?
- 6. Warranty
How long and what are the terms of your warranty?