Infrared Application of the Month:
Drying Water-repellent Coating on Fabric
A carbon mediumwave infrared system from Heraeus Noblelight is helping to increase production line speeds by providing pre-drying of a water repellent coating applied to a specialized fabric used in the manufacture of outdoor clothing. The system's ease of control ensures that there is no damage to the fabric caused by overheating. What's more, the new system has allowed an increase in line speed averaging around 6%.
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Infrared Application of the Month:
Preheating Soundproof Auto Component Sheets
By installing a carbon infrared system to pre-heat acoustic soundproofing sheets prior to moulding, a manufacturer of automotive interior components has significantly reduced production cycle times. And they have also virtually eliminated maintenance costs and machine down-time on one of their primary moulding machines.
The system's use of carbon infrared heating modules from Heraeus Noblelight meant that preheating phase could be eliminated, and hot water radiators and related equipment could be removed, creating more workspace. Energy savings is yet another benefit of the changeover.
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Tech Center Spotlight: Digital Controllers
Single-Loop PID Temperature Process Controllers
Temperature process controllers offers easy to use, accurate, reliable PID control. These single loop panel mount controls include auto-tuning, a universal sensor input and PID control output. Available in standard 1/4 DIN size, these auto-tuning temperature controllers automatically set PID control parameters for optimal system performance. Manual settings also permit on-off, P, PI or PID control modes.
- User-defined menu system allows the user to assign up to 20 paramaters in the operations menu.
- Dual display provides better recognition of process changes, including current process value and set value.
- Ramp to set point feature controls temperature rise.
- Includes a single alarm output as standard.
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Special Designs:
MHS Infrared Modules
Unique sizes and shapes such as curved heated areas or systems requiring a framing for support are typical of the MHS series of heating systems. Completely custom designed for each application, the MHS series offers three-dimensional heating ability and works well with applications that involve additional equipment such as internal conveyor systems. Framing typically from profiled aluminum, with the internal heated areas constructed from high temperature aluminized steel.
Learn more about MHS Infrared Modules from Heraeus Noblelight.
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Non-contact Temperature Measurement and Control
continued from last issue...
Selection of temperature sensors
As the temperature of an object increases the wavelength at which the peak energy occurs decreases. So the temperature sensor should be most sensitive to the wavelengths at which the maximum energy is emitted.
For an object at a given temperature the error in temperature measurement is inversely proportional to the wavelength at which the temperature sensor operates. So generally the pyrometer chosen should be the one operating at the longest possible wavelength.
The amount of energy radiated from a body at a particular temperature depends on the characteristics of the body. Generally, polished metals radiate a smaller proportion of their energy than nonmetals. This property is known as the emissivity, and the lower the emissivity the lower will be the temperature measured.
In simple cases where the emissivity is known the measured temperature can be corrected by dividing by the emissivity.
For cases where the emissivity is low or variable it may be acceptable to paint a surface with a coating of high, constant emissivity. This should be done with caution as the heat lost by radiation will be different for the coated and uncoated surfaces and they will be at a different temperature.
The temperature of a surface can be measured with two pyrometers each viewing different wavelength bands and the ratio of their readings gives an indication of temperature. This type of thermometer is best for targets which are partially obscured by dust or fumes, but if the particles of dust are of the same size as the wavelength being measured the results will be inaccurate so care is needed in choosing suitable applications.
Some of the radiation reaching the surface of a body is reflected and thermometers can not distinguish between this and the radiation from inside the body, except by differences in wavelength between the two.
Thus the most difficult circumstance for measuring temperature occurs when the temperature of a reflective body to be measured is close to the temperature of the surroundings. Very large errors may result if account is not taken of the ambient radiation.
It may be possible to screen off the ambient radiation form the measured area by independent screens or by screens incorporated in the sighting system of the pyrometer. These screens would need to be kept cool. Putting them in good thermal contact with a water jacket may help, but in most cases water cooling is required.
By introducing a second pyrometer to measure the incident radiation from the hot surroundings and comparing this measurement with the first thermometer measurement (for the temperature of the body) electronically, the body temperature can be estimated. This requires that the second thermometer is carefully positioned to obtain an average figure for the incident radiation, from both hot heaters and the cooler reflectors.
Most of the radiation from heaters with quartz envelopes is emitted at wavelengths of less than 5 microns, so a thermometer sensitive to wavelengths above 5 microns would be unaffected by the hot surroundings.
Filters
Infrared pyrometers can be fitted with filters to look only at a segment of the spectrum and integrate the energy falling on the detector from that segment. Filter types include narrow bandpass, wide bandpass and both long wave and short wave pass. Some pyrometers cover most of the infrared spectrum and consequently become sensitive to the atmospheric absorption bands. Many general purpose low cost pyrometers avoid these absorption bands and still provide sufficient energy to make use of low gain amplifiers by accepting the large amount of energy in the range 8-14 microns.
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That's it for this month's issue of Application Notes for IR Heating. Feel free to encourage your colleagues to subscribe. Just click HERE to send them an invitation to subscribe. It's quick, easy, FREE, and no-obligation.
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