While we strive to provide the most accurate measurements possible that are traceable to the National Institute of Standards and Technology, what seems most important to the user is repeatability from reading to reading and from unit to unit. Traceability is vital to the person performing the calibrations to maintain consistency over time, but whether that value is a "perfect" measurement or not does not seem to really matter to most typical users.
Reading to reading repeatability is important because if a user gets different readings for a given set of conditions, he has to be able to rely on the fact that something has changed in his curing system and it is not due to a failure in the measuring device. Additionally, as we address the needs of a global marketplace, larger companies with multiple production locations need to be able to compare data taken with different radiometers so unit to unit repeatability is of major importance.
The accuracy of EIT instruments is specified as +/- 5% typical, +/- 10% guaranteed. This somewhat wide tolerance may sound like we are only guessing but, the truth of the matter is that when measuring UV in industrial processes, 5% is considered leading edge. This is due primarily to the limits of the component technology. Each component of our optical stack has a tolerance. When all of these are summed and the repeatability of each component is taken into account, we are extremely pleased to be able to hold 5%. To do this we must purchase specially matched optical components.
Since it is quite difficult, from a technical standpoint, to cover five orders of magnitude and maintain accuracy, instruments are made in two ranges to cover both low intensity exposure applications, such as printed circuit board and printing plate imaging, as well as high intensity curing applications, such as soldermask curing and ink drying. The UVIRAD is an example of a radiometer designed for low intensity applications and the UV Power Puck is an example of one designed for high intensity applications.
Curing problems do occur from time to time. Without a UV radiometer, it is virtually impossible to solve them. With the cost of having one being so reasonable, there is no rational justification not to own one. The cost is insignificant in comparison to the benefits.
