Guide to UV Measurement
How to Measure - Instrument Basics
The reasons why to measure were covered in the Why to Measure? section of this CD. A review of this section will show two main points:
- Measuring is important because it allows a user to correlate the performance of the process in terms that are universally understood and reproducible.
- Measuring allows a user to save time, save money and communicate process parameters to co-workers, vendors and suppliers.
Still not sure about why you need to measure UV? In your company is there ever a good time for production slowdowns or unscheduled maintenance?
Radiometry is the quantitative measurement of light energy either emitted from a source or striking a surface. This CD concentrates on the measurement of the ultraviolet (UV) portion of the electromagnetic spectrum as it relates to UV curing in industrial processes-the curing of inks, adhesives, coatings and resins. Specific applications and product examples are discussed in the Applications section of this CD.
Radiometers are instruments that give numeric values for the amount of energy. Radiometers use a combination of optic and/or electronic components to collect, process, calculate and display their numeric information. Radiometers report irradiance (W/cm²) and/or energy density (J/cm²) values for the bandwidth of the instrument that you are using. Profiling Radiometers, Spectral radiometers, Radiochromic films and On-line monitors are measurement devices that are discussed elsewhere in this section. It is important to select the right instrument for your measurement needs and then use it properly. It is also important to use data collection techniques consistent with design of the instrument.
Ideally, the energy collected by the detector on the instrument would be exposed in the same manner and in the same point in space as the cure surface on the substrate.
In some curing applications in the real world (web or fiber optics), it is difficult to run an instrument through the process or place the detector in the same point in space as the cure surface on the substrate. The method of curing of application equipment places constraints on the form factor and positioning of radiometric sensors There are several options that will be discussed for these situations but the key to getting numbers that can used for process control in this situation is to position the detector in a repeatable location. Correlations can then be made between your readings and the condition of your UV system.
There are several ways to classify instruments. In the Instrument Basics section, topics covered include:
- Instrument Analogy
- Absolute and Relative Readings
- Dynamic and Static Measurements
- Measurement Strategies
- Instrument Use Tips
Expectations of UV measurement instruments often exceed their actual performance with users sometimes expecting performance to be within a small fraction of a percent - similar to a precision thermometer or voltmeter. The combination and interaction of the optics and the electronics and how the instrument is used determine how well it performs. More detail on the performance of instruments and calibration issues are discussed in the Instrument Advanced section.