Radiometric calibration of equipment

Introduction: History of the calibration

A few thousands of years, the Egyptians developed a traceable measurement system, now known as metrology. In the days of kings and pharaohs, a block of granite measured by a pharaoh from the forearm to the tip of your index finger, plus the width of the palm, became a reference for the length (The Royal Egyptian Cubit). Architects, engineers, craftsmen and builders of pyramids, tombs and temples used since this reference. The result of this measure and the traceability of the Egyptian Royal Cubit The is still today one of the great wonders of history. The pyramids were built with an error rate of + - 0.05%. This means that for every 125 feet, the Egyptian builders failed! Less than an inch! One might note that, if the holders of the Royal Egyptian Cubit The do not carry your copy weekly to compare with the teacher, would lack the death penalty! (If you are interested in this story and give credit, please visit: http://www.ncsli.org/misc/cubit.cfm (English)).

What is the calibration of an instrument and what is it?

Calibration of an instrument is the act of comparing the fundamental units of measurement of the instrument with another instrument. This comparison tool is able to give a more accurate reading of the same stimulus was measured and compared with a more precise tool.

The increasingly strict chain of comparisons is subject to national or international. In the U.S., this agency would be the National Institute of Standards and Technology (NIST). The NIST uses the natural phenomena of physics to set the units of measurement. The temperature measurement incorporates the use of the standard 100 ohm 0385 Platinum Resistance Detectors "Platinum Resistance Detectors" (SPRTD or SRTD), in relation to the freezing point of certain metals or triple point of water (the phenomenon of nature that few elements or compounds share the point of temperature / pressure that distilled water is solid / liquid or gaseous).

For measurements of radiant energy, environmental an appendix added to the contact temperature sensor built into a nearly perfect radiator materials. These sources refer to the primary rules. A primary rule is considered as accurate as you will obtener.Cuando accuracies are combined into a total uncertainty for the instrument, the result is used to measure a stimulus with a degree of certainty in measurement.

This gives you the opportunity to obtain a measurement point can be repeated (when taken in similar circumstances) in another time and any place on earth. It also establishes a basis for the unexpected event, such as ice cubes begin to thaw about 32 degrees F above the 0m. at sea level. When it comes to calibration of any instrument, the terms accuracy, tolerance and uncertainty are often used interchangeably and the like. But they are not. These terms are explained in detail or just say they are topics in themselves.

For the purpose of this presentation, accuracy is a statement of possible limits of error for a particular parameter of an instrument under specific conditions. The total error for that instrument would only tolerance of the instrument. Most measuring instruments have several errors that may affect the measurements shown.

When combined, these errors, first with errors of the same instrument (directly related to an instrument, tolerance), then the total errors of the additional instruments used in conjunction with a displayed value (ie, an instrument loop) the result is a total uncertainty of reading.

Perhaps an example may clarify: The recommended air pressure for a brand of tires on a vehicle model. A newsletter informs users of the pressure above and the recommended pressure. But how can the user ensure that the pressure is read on another continent with a different instrument, correct? The answer is a science known as http://www.blogger.com/es.wikipedia.org/wiki/Metrolog% C3% ADa Metrology, which are the registration and calibration systems necessary to provide assurance of an accurate traceability instrument (to NIST or other organization).

Another example would be the chair you are sitting you. It is likely that the parts used to build and manufacture the chair upholstered or are manufactured in more than one site. How do the pieces fit so well, the paint or chrome, or printing of the packaging is so uniform? and certainly has gone through a number of containers and machines. The answer lies in accurate measurements repeated exchange of instruments of the same chain of precisión.Ahora good measure, why the radiometric calibration? The answer to this question lies in its use of the equipment:

If you:

A. Use specific temperatures related to IRB. Delta uses IRC related temperatures. Use images with their corresponding temperatures nuances involving visualizadaD image. Use comparative data to other IR related instrumentaciónUsted is probably a thermograph.

If you are a thermometer, will be more properly related thermal data that can only be made with calibrated instruments. NO-calibrated instruments, sometimes they are good enough to provide an indication that an object may be hot or cold. The fact is that it can not be demonstrated.

Analyze your results is the fundamental reason for calibration. If the instrument is calibrated and the client (or his lawyer) asks: "Is the object in question so hot or cold as you claim?" The simple answer is yes. The complex response would include a degree of accuracy tolerancia.La cameras and calibration standards, the basic statement of accuracy for the images are not included (normally) the inaccuracies of your computer. It is said that the temperature will visit + - some values ​​(often 2% of full scale reading) to a set temperature and some values ​​above this temperature. The accuracy of the calibration of the instrument must be at least 1 / 3 to 1 / 4 of its instrument of precision (ie, 2% by instrument, a standard must be from 0.67 to 0.5% of full scale reading).

As an example, consider:

A chamber of accuracy is + - 2 ° C to 100 ° C or + - 2% of reading. This declared value, to say, 250 degrees C, the instrument can read now from 245 to 255 degrees C (+ - 5 degrees C). When it comes to radiant temperature, this type of accuracy (ie, 0.5 %) is difficult to obtain. The reason is that the emissivity (E), reflectivity (R) and transmission (T) tend to induce errors greater than or equal to 2% of value shown. For this reason, the primary rules of radiant energy are usually performed in the laboratory. These rules are intended to greatly reduce errors ERT. R and T in these rules will be negligible and E is 0.995 and a maximum in most cases. These standards are set by themselves (usually) + - 1 to 2% or less of reading or full scale. Importantly, these standards often derive their value from the temperature control and cooling thermometry built and because of this it may be calibrated to greater tolerance, if necessary.

Calibration Certification

Calibration Certification is intended to quality and provide a legal instrument for a manufacturer, user or client to ensure the values ​​of a physical reality. In its simplest form, certification is a document intended to be traceable, for: repeatable accuracy in the statements, the identity of instrumentation, instrument holders and performers of the calibration

Calibration standard for Infrared Cameras / Thermal Imaging

If you send your team to be calibrated infrared thermal imagers, chances are that the black body is used and the range of costs used, from about $ 500.00 new, up to $ 1500.00 or more, plus the cost of certificates traceability. So how do you calibrate an instrument at home or office, for example, at a lower cost?

One of the most common techniques is to freeze or just take distilled water to a boil, and observe the temperature of the spacecraft with radiometry. This requires: ensuring that his ship is large enough to ensure that the size of your radiometry is below the surface ship observada.Que observed by radiometric surface is flat and perpendicular to the plane of observador.Que is can reasonably determine that the vessel surface S and the exercise of its powers II.Que level lighting and other heat sources minimally impact (RT). They use traceable contact thermometer to ensure the expected lecturaNotas: Keep your records as when does the maintenance of reports for their clients. You will need to exercise the repeatability between obtaining annual readings, to discuss where, when and how to perform the calibration.

How often should I calibrate or validate an instrument?

Normally, the instruments IR (Infrared) are calibrated or verified annually. A simple and single point of validation of their radiometric, often performed before performing a scan. Validation is a concept to ensure, and usually does not require much time and calibration.

Calibrate Cost

Radiometrically calibrated using third parties such as a calibration laboratory or the manufacturer of the calibration laboratory is expensive. Manufacturers are often the only source of radiometric correction. This is due to the use of proprietary software in the radiometry.

Laboratory calibrations are not the manufacturer will only be able to provide evidence that radiometric traceability is within the manufacturer or its specifications. If you intend to spend more money to get your own black body (highly recommended if you use Thermography Level II), some sources have been listed at the end of this article. A more complete description of traceability and an excellent source of key terms in the calibration are provided by the NIST at:

http://ts.nist.gov/traceability/

http://ts.nist.gov/traceability/suppl_matls_for_nist_policy_rev. HTM

References

1. Amperis - Measuring instruments - Cameras Termográficas2. Web National Institute of Standards and Technology USA (English): http://www.nist.gov3. ANSI / NCSL Z540-2-1997 American National Standard for Expressing Uncertainty, U.S. Guide to the Expression of Uncertainty in Measurement4. Infraspection Institute's Level II Certified Infrared thermographer Reference Manual