Measurement of ultraviolet intensity and temperature inside a UV system has always been a difficult, if not impossible, task. For example, UV cured products are often exposed to UV light in a conveyorized, multilamp system which produces intense UV radiation and temperatures of several hundred degrees. It is often desirable to determine the UV intensity, total energy and product temperature during its passage through the system. Such data in the past has been very difficult to obtain because of mechanical inaccessibility, high temperature, and intense UV.

General Description

UVIMAP, a member of EIT's family of UV measurement and control instruments, makes UV and temperature measurement simple and straightforward. The small, battery-powered instrument can be placed directly into the curing environment where it measures UV intensity and temperature as a function of time. The resulting measurements are digitized and stored within the instrument. Upon completion of a measurement run, the instrument can be connected to a separate, self-contained, thermal printer which automatically plots the results.

The instrument can also transfer its data to an IBM compatible personal computer where the data is available in tabular form. The data may be printed in hard copy form and may also be stored on floppy or hard disk in database format. The complete system provides a convenient means of measuring, storing and providing hard copy UV and temperature data. The system also provides the means for a data base and graphs for future analysis of the UV process.

Technical Description

The measuring instrument is housed in a specially fabricated fiberglass/aluminum housing measuring 9 1/8 x 5 x 1/2 inches, designed to withstand high temperatures for short periods. It contains a UV filter-sensor combination which provides the same very high opto-electronic performance which is provided by other EIT instruments. The filter-sensor measures UV radiation incident on the top surface of the package. The sensor output is then digitized and stored in Random Access Memory (RAM) under microprocessor control. Up to 4000 UV and 2000 temperature measurements can be stored. Upon completion of a measurement cycle, the instrument can be connected to the printer or to an IBM PC compatible computer where the data can be presented in tabular form and/or stored on floppy or hard disk.

When used with its printer, the UVIMAP automatically annotates and plots data. Before plotting the measurement data, the Total (integrated) UV energy, Peak value of UV intensity, Average UV intensity, UV sample rate, Peak value of temperature, and the Number of sample points are summarized and printed.

Simplified Operation

The instrument features controls to provide maximum operating flexibility, making it ideally suited for many different applications. A Sample Rate Select switch provides user selectable data sample rates of 5, 10, 20 and 40 samples per second. A Range switch provides full scale UV inputs from 0.1W/cm2 to 5W/cm2 for high power units and from 5mW/cm2 to 100mW/cm2 for low power units. The Temperature Range switch provides 4 full scale temperature ranges from 0 to 50 degrees, 100 degrees, 200 degrees and 400 degrees C.

Plotting step size permits plotting each data point on 0.35mm to 2.8mm distances between points, effectively compressing or expanding the data. Power/Mode and Start/Stop allow the instrument to collect data manually or automattically after crossing a preset UV threshold value. The interface cable hooked up to this instrument determines whether the data is to be plotted or transferred to a PC.

Rechargeable Batteries

The instrument is powered by rechargeable batteries and will operate for six hours without recharge. The instrument is provided with a special battery charger which will recharge instrument batteries in 14 hours maximum. The printer is powered from 120 VAC, 60Hz, or 220 VAC, 50Hz to be specified at time of order. The printer also operates on rechargeable Ni-Cad batteries.

Applications

UVIMAP provides the capability of measuring and plotting previously unobtainable UV intensity and temperature data. Some typical applications are:

• Characterizations of Curing Conditions - Figure 1 below shows UV intensity and temperature profiles seen by a printed circuit board as it traversed a 3 lamp, 200W/inch UV curing system. Note that peak UV intensity was about 170mW/cm2 and that lamp #2 was sharply focused. Lamp #1 is defocused as evidenced by the dual peaks. Also, note the deteriorated reflectivity of lamp #3 as indicated by the rounded peak. None of these conditions could be determined by the unaided eye. Peak temperature at the top surface of the board was 85.6 degrees C. Measurement of material surface temperature provides the ability to avoid thermal damage to the material during UV processing.
  
  Figure 1. UV/Temperature profile of conveyorized system.

• Resin Curing - Figure 2 below shows UV intensity/temperature history of a 0.005" polyester-UV curable resin - 0.005" polyester sandwich. The sandwich was placed under a UV flourescent lamp and the UVIMAP thermocouple placed in the resin. The UV lamp output rose to a maximum of approximately 3.5 mW/cm2. Initial resin temperature was about 23 degrees C and peaked to a maximum of about 132 degrees C after about 1 minute. The lamp was extinguished after 3 minutes. However, polymerization, as evidenced by a continued temperature rise, had been completed 1.5 minutes earlier. Such information provides a valuable insight into the curing process.
  
  Figure 2. UV/Temperature profile of stationary system.