Typical temperature control measurements using infrared in industry:

Typical temperature control measurements using infrared in industry:

• Generators, drives, power units
• Bearing shells
• Switch cabinets
• Electronic circuits
• Bimetal shift point setting
• Heat setting, drying and laminating processes
• Running rubber tyres
• Plastics in drying and forming processes.

Typical temperature control measurements using infrared in building/air conditioning technology:

• Ventilation ducts
• Heat profiles and thermal insulation in buildings
• Localisation of cold bridges and insulation weak points.

Typical infrared applications in heating engineering:
Surface measurements on:

• Radiators, painted heating pipes
• Floor coverings, wood, cork, tiles, granite and unfinished wall surfaces for the localization of heating pipes.

Typical infrared applications in food inspection:

• Quick test in Incoming Goods or in a chest freezer.

Contact temperature measurement is...
...ideal for:

• Measurement of smooth surfaces with good thermal conductance such as all metals. In this case, contact measurement is usually also more accurate than infrared measurement.

b) Determination of core temperatures in liquids and food. 
...conditionally suitable for:

• Measurements of poor thermal conductors (for examples, see IR measurement)

A probe for contact measurement can only display correct tempera-tures if it can take on the temper-ature of the measurement body. 
With poor thermal conductors, this will mean faulty measurements or very long adjustment times until the probe has taken on the temperature of the measurement object.

• For small, low-mass parts.

Here, the contact probe draws heat from the measurement object, which influences the measurement result.

...not suitable for:

• Parts that must not be touched (see above)
• Moving parts.

Typical contact measurement applications in industry on:

• Tools for forming processes
• Drives, gearboxes, bearings

– All metal surfaces and for comparison measurement with the IR measurement, in order to be able to establish the emission level of the surface.

Typical contact measurement applications in building/air conditioning technology on:

• Ventilation ducts
• Wall surfaces.

Typical contact measurement applications in heating engineering:

• Measurement of flow/return temperature on bare copper pipes
• Radiator inspection
• Localisation of heating pipes in the floor and in walls

Typical contact measurement applications in food inspection:

• Measurement of core temperature at critical product temperatures

Summary: non-contact measurement or contact measurement – Testo's recommendation

Non-contact infrared temperature measurement is...
...ideal for measuring the surface temperatures of:

a)         Poor thermal conductors such as ceramic, plastic, rubber, wood, paper, wallpaper, plaster, textiles, organic materials, food. 
The measuring instrument measures without any retroactive effect, i.e. without any influence on the meas-urement object. The IR radiation of the measurement object is therefore always at the same speed, irrespec-tive of thermal conductance. 

b)         Materials with a high emission level, e.g. lacquer, paints, glass, minerals, tiles, stone, tar and all non-metallic materials. In this case, an emission level setting of 0.95 is usually correct. Errors due to external radiation reflected on the surface are only slight. 
c) Moving parts (provided that the material has a high emission level or a material with a defined emission level can be applied) e.g. running paper webs, rotating tyres or oxi-dised steel parts on a conveyor.
d) Parts that must not be touched such as freshly painted parts, sterilised parts or aggressive media or live parts such as electronic compo-nents, busbars and transformers. 
e) Small and low-mass parts, e.g. components and all measurement objects where a contact probe draws too much heat, thereby causing incorrect measurements.

However, you must always ensure that the measuring spot of the measuring instrument is smaller than the measurement object!
...only conditionally suitable for:
Metal oxides, as these have an emission level that is mainly dependent on the temperature (between 0.3 and 0.9).
In this case, you should either apply a substance with a defined emission level (e.g. testo emission tape order-no. 0554 0051, lacquer or oil) or determine the emission level by means of a comparisonmeasurement with a contact thermometer.

...not suitable:
For bare metals to which no materials that increase emission level such as tape, lacquer or oils can be applied. Here, a high error rate can be expected due to the high level of reflection on the measurement object surface.

Further practical tips Infrared measuring instruments

Natural objects in open air such as water, stone, earth, sand, plants, wood, etc. have emission levels between 0.8 and 0.95 in the spectral range 8 and 14 µm. If measurement is to be performed in the open air, it may be necessary to take “cold sky radiation” into account in the case of small emission levels. Wherever possible, however, this “ambient radiation” should lie in the proximity of the air temperature. This is achieved by screening the interfering radiation, e.g. with a box or an umbrella over the measuring point.
-> Measurable with Testo IR measuring instruments Glass and quartz Have high emission levels of approx. 0.90 in the wavelength range over 8 µm. Non-transmissive to IR, i.e. the glass pane is measured.

-> Measurable with Testo IR measuring instruments Plastics Are measured in the temperature range between +20 °C and +300 °C during drying and forming processes, extrusion, calendering, deep-drawing, etc. The emission level of almost all plastics is between 0.8 and 0.95, and is therefore easy to measure.
-> Measurable with Testo IR measuring instruments Transparent films Have, at certain wavelengths, a characteristic absorption band, which means that the emission level is, however, dependent on the thickness of the film. The thinner the film, the lower the emission level. Thin films are often transmissive in the IR range. Take the background into account.

-> Conditionally measurable with Testo IR measuring instruments Hot gases and flames Are “volumetric radiators with selective emission characteristics”. The measuring point is no longer planar. The average temperature value is taken from a section inside the flame. This value is also frequently influenced by furnace walls behind the flame or gases. As with transparent materials, flames and gases radiate primarily in certain spectral ranges, for example in the range around 4.3 µm (CO2 band).
-> Measurable with special instruments -> No measurable with Testo IR measuring instruments

Comparison of an infrared thermometer and thermal imager

Particularly with multi-point temperature measurement on large objects, IR measuring technology with an IR thermometer (pyrometer) is, also thanks to its comparably low price, seen as a simple non-contact measuring solution. For the measuring tasks described here, these instruments are more than adequate.

In contrast, however, the testo 870 thermal imager, for example, has 19,200 individual temperature values, which are used to create an IR image. In practice, this means the following advantages:

• Detection of critical temperatures even on extremely small objects, e.g. a hot cable. 
• Large surfaces or measurement objects (e.g. floors, buildings, switch cabinets, etc.) are shown on one image. There is no longer any need to carry out time-consuming “scanning” of a surface with an IR thermometer. 
• Documentation of measurement result as an IR image and real image at the touch of a button

These features may be decisive in industrial maintenance, for example, where faulty machinery parts such as an overheated motor have to be quickly detected to enable them to be replaced immediately in order to avoid downtime. Most available thermal imagers now also have a digital camera. This means that both a thermal image and a visual image of the measurement object are captured, ensuring better orientation during analysis. Tip: Essentially, if you have found the point at which you want to take a measurement, i.e. you know where to measure and are not dependent on the ambient temperature, and then a single-point pyrometer is adequate. For example, to measure fruit or the temperature in refrigerated displays, it is not necessary to use a thermal imager.
However, if you need to detect danger spots without knowing beforehand where they are, a thermal imager can bring considerable advantages.

Testing and calibration

To test and calibrate the display of radiation pyrometers, a black body radiator is required. During calibration, it is important to ensure that the respective measuring field of the radiation thermometer to be tested is smaller than the opening of the black body radiator.
In the case of a permanently set emission level (e.g. 0.95), the display must be converted to ε = 1.

Emission level
Even if the emission level is correctly set, measurement errors may occur!
With emission levels less than 1, the measuring value is extrapolated on the basis of instrument temperature   ambient temperature.
– If the instrument temperature does not correspond to the ambient temperature, the instrument's emission level correction will be incorrect. In other words: if the instrument temperature is lower, then the measurement result is too high, and if the instrument temperature is higher, then the measurement result is too low. 
– If individual heat or cold radiators (e.g. heating elements, lamps, refrigeration units, etc.) are reflected on the surface of the measurement object, then this radiation does not correspond to ambient temperature 

= instrument temperature. In this case too, the emission level correction performed by the instrument will be incorrect.

Remedy: Screen off such radiators, e.g. with a cardboard box. This will absorb any stray radiation and emit its own radiation ambient temperature.

Temperature check on ventilation ducts.

Temperature check on ventilation ducts.

Points to watch out for:
– The air is not measured, but rather the temperature of the grilles.
– Do not take measurement on bare metals.
– Do not take measurement too close to the measuring point.
Checking heat profiles or detecting critical points in buildings.

Points to watch out for:
– Materials such as wallpaper, wood, plaster, painted window frames and glass are easy to measure due to their high emission level of between 0.9 and 0.95.
– Either measure bare metal frames with a contact thermometer or apply a coating that increases the emission level.

Monitoring the thermal insulation in buildings.

Points to watch out for:
– Do not take measurement on bare metals.
– Note differences in emission levels
General applications of infrared measuring technology

Quick temperature measurement for road construction.
Points to watch out for:
– Permissible operating temperatures of measuring instrument
– Measuring spot/measuring distance
– Measuring instrument must have adjusted to ambient temperature.

– Only measure materials with
A high emission level, as “cold sky radiation” at -50 to -60 °C present a disturbance variable. If necessary, screen the sky e.g. with an umbrella over the measuring point.
Tip: Use a measuring instrument with a small measuring spot at a large distance.

In food inspection
Points to watch out for:
– Only surface temperature is determined contactless.
=> In the case of critical values, always verify with contact thermometer!
– Observe measuring spot/measuring distance
– Measuring instrument must have adjusted to ambient temperature.
– The ideal distance between measur-ing instrument and cooled product/ packaging is 1 to 2 cm. Outer card-board packaging should be opened and the measurement taken inside the packaging.
– With film-sealed food, only the temperature of the film is measured. Therefore only measure at points at which the film is in direct contact with the product.
– Do not measure at occlusions.
Tip: Use combi measuring instrument (e.g. testo 104 IR)

Infrared measuring technology Industrial applications

Detection of excessively high temperatures on switch cabinets, measurement on electrical circuits, such as resistors, transistors in printed circuits, etc.

Points to watch out for:
– Measuring spot/measuring distance
– Measurement not on bare surfaces (they reflect the ambient temperature), but on plastic with ε setting 0.95.
Tip: Use an IR measuring instrument with a small measuring spot (e.g. testo 845, testo 830-T3)

Temperature measurement on refrigeration unit

Points to watch out for:
– Measuring spot/measuring distance
– Measurement on surface with a high emission level (e.g. painted surface)
Tip: Use a measuring instrument that has a small measuring spot at a large distance and permits a comparison measurement using a contact thermometer (e.g. testo 845 or 835 set).

Checking and recording temperature values on generators and drives, on diesel units and on exhaust manifolds.
Points to watch out for:
– Measuring spot/measuring distance 
– Measurement on surface with a high emission level or moisten surface, e.g. with oil. 
Tip: Use a measuring instrument that has a small measuring spot at a large distance and permits a comparison measurement using a contact thermometer (testo 845 and 835).

Temperature check on output cables of an electricity generator.
Temperature check on rail vehicles, e.g. “hot box detection” on railway carriages through measurement of axle covers temperatures.
Points to watch out for:
– Use a measuring instrument that has a small measuring spot at a large distance. 
Heating, ventilation and air conditioning systems

History of infrared measuring technology

Up until 1960, radiation thermometers are primarily used to measure high temperatures. However, after that time, various types of radiation detectors that are also receptive to wavelengths larger than 8 µm are developed, enabling reliable and accurate temperature measurement right down to below the freezing point of water.

• 1800    Herschel discovers the IR spectrum through tests with a liquid thermometer with IR-absorbing ball
• 1900 Planckian radiation laws
• 1938    Book “Optical Pyrometer” (measuring technology application)

Guidelines for infrared measuring techniques

Infrared temperature measuring instruments are particularly suitable for...

• ...poor thermal conductors, such as ceramic, rubber, plastics, etc. A probe for contact measurement can only display the correct temperature if it can take on the temperature of the measurement body. With poor thermal conductors, this is generally not the case or response times are extremely long.
• ...for determining the surface temperature of rough surfaces (e.g. plaster, textured wallpaper, etc.). Measurement with probes can only sometimes be carried out due to the poor thermal contact.
• ...for moving parts, e.g. running paper webs, rotating tyres, running sheet metal webs, etc.
• ...for parts that must not be touched, e.g. food, painted parts, sterile parts or aggressive media.
• ...for live parts, e.g. electrical components, busbars, transformers, etc.
• ...for small and low-mass parts, e.g. components and all measurement objects where a contact probe draws too much heat, thereby causing incorrect measurements.
• ...for the measurement of extremely small or extremely large surfaces through the selection of various lenses.

Advantages of infrared measuring technology

There has been a huge increase in applications involving infrared measuring systems in recent years. The following factors undoubtedly play an important part in this trend.
Infrared measuring technology offers easy temperature capture and quick, dynamic processes. This is enhanced by the short response time of the sensors and systems. 
The systems offer sophisticated, modern technology with reliable sensors and modern microprocessor electronics. 
Their absence of interaction, i.e. they do not influence the measurement object, permits online measurements of sensitive surfaces and sterile products, as well as measurements in hazardous or inaccessible areas. 
Another factor in this trend that should not be ignored, over and above the technical advantages, is that these systems are attractively priced for customers as a result of cost-optimized production processes, which place the emphasis on high unit totals.

Thermal radiation

It is common knowledge that all bodies, depending on their temperature, emit electromagnetic waves, i.e. radiation. Energy is transported along with this radiation, ultimately permitting non-contact measurement of the body's temperature with the help of the radiation.
The radiated energy and its characteristic wavelengths primarily depend on the temperature of the radiating body.
Ideally, a measurement object will take on all the energy (absorption) and convert it into its own heat radiation (emission). In such cases it is referred to as a “black body radiator”. Such behavior virtually never occurs in nature; rather, additional reflection and transmission of the radiation at or through a body occurs.
However, in order to nevertheless obtain reliable measurements with infrared measurement systems in practice, it is necessary to identify this emission, reflection and transmission behavior (also see 1.4) accurately or to eliminate this influence by suitable means.
This can be achieved with the aid of reference measurements using contact thermometers or by deliberately modifying the measuring area to make it suitable for infrared measuring technology, e.g. by applying lacquer coatings, adhesive and glue, plastic coatings or paper stickers.

Whether and how these measures are to be performed depends ultimately on the measurement object and the measurement environment. Classifying applications according to the appearance of the measurement objects and their surface helps when assessing this.