Fluke Ti20 User Manual download pdf (Page 59)

Appendices

Basics of Infrared Measurement B

B-3

Q. What is the distance to spot ratio?

A. The optical system of an infrared thermometer collects the infrared energy from a

circular measurement spot and focuses it on the detector. Optical resolution is defined by

the ratio of the distance from instrument to the object compared to the size of the spot

being measured (D:S ratio). The larger the ratio number the better the instrument’s

resolution, and the smaller the spot size that can be measured. The laser sighting included

in some instruments only helps to aim at the measured spot.

A recent innovation in infrared optics is the addition of a Close Focus feature, which

provides accurate measurement of small target areas without including unwanted

background temperatures.

Make sure that the target is larger than the spot size the unit is measuring. The smaller the

target, the closer you should be to it. When accuracy is critical make sure that the target is

at least twice as large as the spot size.

Q. How to take temperature measurement?

A. To take a temperature measurement, just point the unit at the object you wish to

measure. Be sure to consider distance-to-spot size ratio and field of view. There are

important things to keep in mind while using infrared thermometers:

• Measure surface temperature only. The IR thermometer cannot measure internal

temperatures.

• Do not take temperature measurement through glass. Glass has very distinctive

reflection and transmission properties that do not allow accurate infrared

temperature reading. Infrared thermometers are not recommended for use in

measuring shiny or polished metal surfaces (stainless steel, aluminum, etc.). (See

Emissivity.)

• Watch for environmental conditions. Steam, dust, smoke, etc., can prevent

accurate measurement by obstructing the unit’s optics.

• Watch for ambient temperatures. If the thermometer is exposed to abrupt ambient

temperature differences of 10 degrees or more, allow it to adjust to the new

ambient temperature for at least twenty minutes.

Q. What are some uses for non-contact thermometers?.

A. The most popular uses include:

• Predictive and Preventive Industrial Maintenance: check transformers, electrical

panels, connectors, switchgear, rotating equipment, furnaces and much more.

• Automotive: Diagnose cylinder heads and heating/cooling systems.

• HVAC/R: Monitor air stratification, supply/return registers and furnace

performance.

• Food Service & Safety: Scan holding, serving, and storage temperatures.

• Process Control & Monitoring: check process temperature of steel, glass, plastics,

cement, paper, food & beverage

For additional information on applications for non-contact IR thermometers visit our

website at www.fluke.com/thermography

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Fluke Ti20 User Manual Page 59

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