Guide to UV Measurement
Instrument Basics - Measurement Strategies
When designing, developing and bringing new UV measurement instrument to market, a manufacturer identifies a need or application that they feel will benefit from a new or improved product. Market research and testing of prototype units allows the manufacturer to refine and improve the product before it is released.
Often the manufacturer has an idea or two about how an instrument can be used to measure UV. End users, who know their equipment and process better than anyone else often take an instrument along with some imagination and ingenuity and use it in ways never imagined by the manufacturer.
This section offers thoughts, suggestions, tips and ideas on measurement strategies for different types of equipment. The strategies should be viewed as starting points and adopted for your individual process. Hopefully some of the ideas will hit home and get the creative thoughts flowing with your staff members.
General Suggestions
- Involve your suppliers and staff early in the process. Use the knowledge of your formulator, substrate supplier, equipment manufacturer, UV systems manufacturer, UV instrument manufacturer, equipment operator and quality assurance staff to discuss ideas. Use the experience along with some imagination and ingenuity from all the people that you involve.
- Decide what UV bandwidth(s) are most important to your process and what will be measured.
- Find a repeatable way to position or use the measurement device and document the ‘right' way to do it. Build the ‘right' way into your training or ISO procedures.
- Assign ownership and responsibility of the process.
- Establish good communication procedures within your company (single or multiple lines or locations) and with your suppliers.
Conveyor Systems
- Conveyor Systems are often the easiest to measure UV because the space to fit an instrument is not limited.
- There are a wide variety of instruments (radiometers, profiling radiometers) that can be looked at first for measuring the UV on conveyor systems.
- Establish a uniform speed that you will use to take your measurements. The speed used should be slow enough that the instrument can pass through the system without getting damaged and the irradiance values can be accurately measured by the sampling rate of the instrument.
- Extrapolate the energy density readings for faster line speeds. link to Data Collection Speeds
- Watch for loose conveyor belts and ‘bouncing' radiometers.
- Establish the instrument orientation and position on the conveyor where you will take the measurement.
- On wide conveyors, it is a good idea to measure in several places across the width of the system.
- Establish procedures for confirming the lamp type, lamp power, focus height, line speed and other variables on your system.
Web Systems
- Web systems are more challenging because of tight space considerations. Many times there is no way to easily transport a puck style radiometer.
- Look for probe style instruments - radiometers or spectral radiometers. The key to using any of the instruments is that they must be inserted in a repeatable location to get repeatable results. The probe tips cannot be freely waved around under the UV source. Most manufacturers have some sort of locator or mounting kit to use with their instrument. link to location and coordination The reading on your probe will be a measurement at a point in space under the UV system. Even though it is not at the exact cure surface, the reading can be helpful for establishing and maintaining process control. As bulbs age in arc systems, it is a good idea to compare the UV values at the edge of the system to the values closer to the middle of the UV system. This is especially important if your UV system is sized for minimal overlap - your 10” wide web is using a 10” wide UV system.
- Radiochromic films and tabs can be used. Try to match the product to the bandwidth of interest to your process. If the results can be coordinated with absolute reading radiometers, communication is possible with suppliers and vendors.
- Online Monitors are good choices for web systems. Ideally, the sensor would monitor both the reflected and direct UV energy from the system. link to sensor mounting locations In the real world this is not always possible based on the type of application equipment and UV system.
- Small miniature radiometers have been used on some web systems, but check first to make sure that the unit will not get caught in rollers or nips.
- Some companies with webs have built test fixtures in which the UV system is pulled off the equipment or press and then checked on the test fixture with a radiometer or profiling radiometer.
Small Part/Flood Lamps
- It is important to try and align the detector with the same plane as the object being cured.
- You may be able to use your standard radiometer. If a puck style radiometer or profiling radiometer will work consider this first. The size and dynamic range of the instrument are important considerations.
- Miniature radiometers are available that can be inserted into the small flood cure chamber and removed to display their reading.
- Consider radiometers with remote heads that are tethered via a wire or cable to their display/processing unit.
- Online sensors can also be used with some small part/flood systems.
Multiple Lamps
Spot Cure
- Many spot cure sources have built in feedback monitors located at or near the lamp source. This can provide a good overview of the UV at the point where it is being generated but not what is coming out of the light guide.
- Hand help portable radiometers can be used at the end of liquid of a fiber light guide. Units with remote heads that are tethered via a wire or cable to their display/processing unit may also work if they can be positioned properly and have sufficient dynamic range for the application.
- Some spot sources have feedback loops or internal radiometers.
- Consider monitoring of small parts with miniature radiometers.
- On-line monitors mounted near process and work area. In some automated processes, the light guide is brought over to the on-line sensor on a regular interval to confirm the UV output at the tip of the guide.
Dimensional Curing
- Based on the size of the dimensional part, consider a standard size radiometers or profiling radiometers.
- Small miniature radiometers can be used.
- Watch for new instruments that gang together several individual sensors in a system.
- Radiochromic films and tabs can be used. Try to match the product to the bandwidth of interest to your process. If the results can be coordinated with absolute reading radiometers, communication is possible with suppliers and vendors.