- Birthday 03/18/1959
Although your infrared thermometer meets the calibration test, keep in mind that the calibration test/procedure is in a controlled environment - ie: pointing the IR thermometer at a blackbody ( known source ), at a specific distance by a trained instrumentation person. Field of View or Distance Ratio is ONE important component of accurate IR measurement. Think of the IR Thermometer as a Pen Light. If you hold the pen light over your desk about 2" away you will see the light image of a 1/4" circle . When you move the pen light further away the circle gets bigger. 12" inches away the light image is now much bigger in diameter. Now you're viewing/measuring a much bigger area of the blood bag.. The IR Thermometer mentioned earlier by sgoertzen has an 8 to 1 ratio. 8" away from the blood unit has a measuring area of 1" circle/diameter. Movie it closer 4" and you're measuring 1/2" diameter and 2" away you're measuring a 1/4" diameter. If the operator is measuring the unit of blood 24" away the measuring area is now 3" diameter. The laser beam is just a pointing device. The warmest temperature of the unit of blood will be on the outside surface and measuring the blood temperature through a plastic bag will introduce an error if the emissivity is fixed at .95. I checked with an expert who said IR thermometers would need to be set to .85 emissivity to allow for the clear plastic bag. I agree with a previous post that stated the use of an IR Thermometer should be used as a screen ( Go / No Go ) and if out of range use a NIST certified surface thermometer held on the bag for about 8-10 seconds.
How do you specifically measure the temperature? Is the refrigerator door open? How far away was your infrared instrument from the bag? is the blood in a bag or vial? Also, refrigerators have a temperature gradient from front to back. Check the blood in the back - they might be cooler.
It is recommended for users to "validate the IR Thermometer" "A confirmation or guarantee of the accuracy." Comparing the IR reading to a known source. ( which is not easy ) Calibration requires making adjustments to the instrument - usually performed by the manufacturer or calibration lab. IR Thermometers are quick and easy temperature monitoring devices. However, there are "many" pitfalls to infrared when used by untrained personnel. Understanding distance ratio, emissivity and keeping the optics clean and free from obstruction are all important for proper use. Be careful. It would be best use an IR device that has "emissivity" adjustment. Low cost models do not have this. Also determine the best distance to take a reading by understanding the units ratio specification.