Product category:
Monitoring and sensor equipment and systems
News Release from: QHi Group | Subject: Infrared temperature sensors
Edited by the Manufacturingtalk Editorial
Team on 12 August 2003
Infrared sensors check temperatures on
the move
Where the product is moving, fluidised or delicate, the ability to measure temperature on a non-contact basis is a significant advantage, which is where infrared sensors come in.
Temperature is probably the most commonly measured and controlled parameter in manufacturing / process industry Where the object to be measured is stationery, contact thermocouples can normally be used
This article was originally published on Manufacturingtalk on 15 Jul 2003 at 8.00am (UK)
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Infrared thermocouples are small, accurate, non-contact infrared sensors which require no outside power and connect directly to temperature measurement and control instrumentation.
However, where the product is moving, fluidised or delicate, the ability to measure temperature on a non-contact basis is a significant advantage.
So why isn't non contact infrared temperature measurement more prevalent throughout process industry? One major reason is that many process industries were established prior to infrared non-contact solutions being available.
As a result an alternative method of temperature control had to be found.
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Usually this involved measuring the temperature of the heat source and correlating this back to product temperature / quality.
Examples of this include processes, which utilise heated rollers, ovens, mixing, drying etc.
A common theme is that, it is the heat source temperature which is measured and controlled, rather than the product temperature being monitored and used to control the heat source.
However, IR sensors have become small enough and sufficiently low cost to provide an economic as well as technical solution to the problem.
Case Study 1: * Drying oven - major film manufacturer was having trouble maintaining quality on throughput of emulsion coated photographic film.
The problem was that too much heat caused the emulsion to become brittle and crack as it was wound onto spools whilst insufficient heat caused it to stick.
Solution: IR sensors were placed vertically along the conveyor as it passed through the drying oven.
As soon as the evaporation process was complete i.e the emulsion was dry, the surface temperature would immediately escalate to the surrounding ambient temperature.
In this way the drying out point could be precisely determined and no further heat applied to the product.
Thus the heating elements were controlled by monitoring the actual product temperature, as opposed to the other way round.
Case Study 2: * Heated rollers - packaging - a major confectionery manufacturer found that on their packaging lines, the most common cause of stoppage was failure of slip rings used to hold contact thermocouple in place within stainless steel rotating heaters, commonly used in the packaging machinery for fin or lap seals.
In addition it was also found that the thermal lag from middle of the heated roller to point of contact with the packaging material, can be up to 5degC.
Solution: Non-contact IR sensors were mounted to look directly at the external surface of the heaters, reducing set up time for PID control, and increasing PID accuracy, (no thermal lag).
As heaters reach target temperature, measurement control should be switched to a third IR sensor measuring the fin / lap seal, just after its formed by the heaters.
This run speed sensor will then measure the actual seal temperature and can be used to more accurately control heater temperature.
Slip rings are no longer required.
Similar non contact solutions are also available virtually every industry process which uses heat transfer (or it's removal), on products which are moving, fluidised or delicate.
The above solutions are generally applicable to product which have low thermal mass.
However, there are many instances where the thermal mass of the product is such, that the surface temperature is not indicative of core product temperature.
One of the most recent innovations in IR technology has been the patented Speed Boost Equation (SBE), developed by Dr.Francisco Pompei (founder and President of Exergen Corporation), one of the world's leading authorities on the use of IR in industry and medicine.
In essence the SBE utilises a mathematical model to calculate core product temperature via its relationship to the surface temperature.
It requires knowledge and control of input, heat source and exit temperatures, and can enable some dramatic increases in speed, often by elevation of input temperature via pre-heat station.
A specially developed and patented IR non-contact sensor was developed with a heat balance circuit, to retain the "balance" (correlation) between surface and core temperature values.
* Example 1 - a major tyre manufacturer, by monitoring tyre temperature immediately prior to vulcanising, could adjust press time to maximise throughput and thus increase plant capacity by approx.
10%, with no capital investment, (other than temperature control system).
* Example 2 - a major manufacturer of portable kidney dialysis machines required to monitor temperature of blood being transferred through disposable plastic tubing, the IR heat balance sensor measures the internal fluid temperature by measuring both tubing surface and ambient temperatures, then calculating the internal temperature necessary to maintain the heat balance, via the SBE.
The same method can also be employed to measure other fluids within tubing / pipe.
QHi Infrared are exclusive specialist distributors for the Exergen Corporation, and also supply their own thermal monitoring systems (ExerTherm).
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