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ASTM C1064 Temperature Measuring Device

#1
First post here so let me know if I'm doing something wrong.

tl/dr: Anyone know where to get inexpensive thermometers, with 17025 cert, that comply with the requirements of ASTM C1064 for the measuring device?

We have been using cheap dial thermometer that are adjustable and we are unable to verify them at two temperatures 15 degrees C apart to be within 1 F of the reference thermometer. We were told by our calibration company that other companies just buy new ones every year that come with a cert (in our case we would want 17025). We looked into this option and the devices cost around $55, compared to the $6 ones we have been getting. Since we have many inspectors that perform this work, this increase is somewhat prohibitive, so we are looking into trying to get higher quality thermometers and verifying ourselves per ASTM C1064.

The ASTM states that the device has to be capable of accurately measuring the temperature within 1 F throughout the 0 to 50 C range. The 17025 certs that come with the device of interest show a 0.2 C error at 0 and 50 C, with a combined uncertainty of 0.58 C at both values. The stated accuracy is +/- 1 C. I would like to make the argument that the calibration cert demonstrates the capability of the device to measure accurately measure within +/- 1 F between 0 and 50 C, based on error of only 0.2 C at the points of interest. This argument is made more strong due to the method by which accuracy is demonstrated per the ASTM is based on getting values that differ from the reference thermometer (0.5 F accuracy) by no more than 1 F at either test point 15 C or more apart.
 
#2
First post here so let me know if I'm doing something wrong.

tl/dr: Anyone know where to get inexpensive thermometers, with 17025 cert, that comply with the requirements of ASTM C1064 for the measuring device?

We have been using cheap dial thermometer that are adjustable and we are unable to verify them at two temperatures 15 degrees C apart to be within 1 F of the reference thermometer. We were told by our calibration company that other companies just buy new ones every year that come with a cert (in our case we would want 17025). We looked into this option and the devices cost around $55, compared to the $6 ones we have been getting. Since we have many inspectors that perform this work, this increase is somewhat prohibitive, so we are looking into trying to get higher quality thermometers and verifying ourselves per ASTM C1064.

The ASTM states that the device has to be capable of accurately measuring the temperature within 1 F throughout the 0 to 50 C range. The 17025 certs that come with the device of interest show a 0.2 C error at 0 and 50 C, with a combined uncertainty of 0.58 C at both values. The stated accuracy is +/- 1 C. I would like to make the argument that the calibration cert demonstrates the capability of the device to measure accurately measure within +/- 1 F between 0 and 50 C, based on error of only 0.2 C at the points of interest. This argument is made more strong due to the method by which accuracy is demonstrated per the ASTM is based on getting values that differ from the reference thermometer (0.5 F accuracy) by no more than 1 F at either test point 15 C or more apart.

One thing that your calibration company failed to mention is that when you simply replace your thermometer with a new one you have lost measurement traceability. Consider that your thermometer went out of tolerance since it was calibrated and then you just throw it away and replace it. Then you will never know that your measurements were out of tolerance. For 17025, and for any case where knowing whether or not your instrument is in tolerance is important, then you must calibrate it at end of life to check its accuracy.
 
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