Infrared Technology Chips Away at Waste

In a typical gas-fired oven, a series of conveyer belts are used to carry tortilla chips during baking. Variable-rate burners are situated between the belts to sear the chips on each side. The product bakes on the top belt and is then flipped over onto the middle belt going in the opposite direction. The chips are flipped over one more time onto the bottom belt to complete the baking process. The chips exit the oven in the same direction they entered (Figure 1, p. 44).

During the preparation of corn tortilla chips, fast heating of both product surfaces is essential for retaining a suitable moisture level inside the chips. The baking process depends on precise control of belt temperature inside the oven; the tortilla chips must be seared in a way that bakes in flavor without leaving visible burn marks.

Accurate Temperature Readings Are Key

In the past, most tortilla equipment manufacturers utilized thermocouples to indicate the ambient air temperature inside their ovens. Thermocouples consist of two strips or wires of different metals, joined at one end. Changes in temperature at their junction induce a change in electromotive force (emf) measurable across the leads. As temperature rises, the thermocouple emf rises. Sometimes an array of thermocouples, aptly called a thermopile, is used.

A thermocouple is one type of contact temperature sensor and is the cheapest and easiest to use. Nevertheless, thermocouples are incapable of measuring direct surface temperatures. Their readings may not accurately reflect oven conditions during process heating. This drawback limits the ability of tortilla and tortilla chip factories to optimize baking cycles during production runs.

Increasingly, manufacturers of process heating equipment are choosing IR temperature measurement technology over traditional thermocouples. IR thermometers are useful for measuring temperature under circumstances in which thermocouples or other probe-type sensors, for a variety of reasons, cannot be utilized or do not produce accurate data. A unique characteristic of IR thermometers is their ability to determine the temperature of an object without making physical contact with it.

The principle of IR and its non-contact nature offers many advantages for process ovens. IR temperature monitoring eliminates the risk of contaminating the product, a feature which is extremely important in the food processing industry. Furthermore, IR sensors save time and money in situations where another type of contact sensor would require that machines be shut down.

IR instruments measure temperature according to Planck’s Law of blackbody radiation, which states that every object emits radiant energy and that the intensity of this radiation is a function of the object’s temperature. The sensor finds an object’s temperature simply by measuring the intensity of radiation.

An IR thermometer can be compared to the human eye. The lens of the eye represents the optics through which the radiation (flow of photons) from the object reaches the photosensitive layer (retina) via the atmosphere. This is converted into a signal that is sent to the brain after being compensated for ambient temperature variation (Figure 2, p. 45).

Every form of matter with a temperature above absolute zero emits infrared radiation according to its temperature. The internal mechanical movement of molecules causes this phenomenon, known as characteristic radiation. The intensity of this movement depends on the temperature of the object. Because the molecule movement represents charge displacement, electromagnetic radiation (photon particles) is emitted. These photons move at the speed of light and behave according to the known optical principles. They can be deflected, focused with a lens, or reflected from reflective surfaces.

Sensor Advancements

For its current oven designs, Casa Herrera employs the Raytek Thermalert TX infrared temperature sensor (Raytek Corp.; Santa Cruz, Calif.; Figure 3, right). This device combines non-contact temperature measurement with industry standard two-wire technology. The sensor provides digital communications and 4-20 mA output, allowing remote configuration and monitoring. If needed, multiple sensors can be installed on a single multi-drop network.