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Posts posted by JohnD
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These are our findings as to the pros and cons of electronic temperature probes.
Thermocouple Probes. Stable, have a large inaccuracy, but are not susceptible to physical shock.
RTD, SPRTD,PRTD. Very accurate, but susceptible to physical shock which can put them out of calibration. Used at NIST and most calibration labs. Good when handled with care.
Thermistors. Very accurate but have a limited temperature range and are not susceptible to physical shock.
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Some manufactures of liquid in glass thermometers only determine the zero point during manufacturing and expand the scale from that point. It has been our experience when purchasing thermometers for our customers a small percentage won't pass a multi point calibration because they were only checked at one point and expanding the scale from that point which leads to errors if capillary and the length of the glass aren't always the same. Our customers define the temperature points that they commonly use and if they don't we calibrate the full range and always include a 0c point.
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If a company choices to use its own mythology to calibrate any devices.They should have documented uncertainties of the processes and be able to prove that the methods are reproducible iif they are doing calibrations outside the scope of any governing bodies ie NIST and ANSI defined requirements. If not then what is being done isn't traceable back to the NIST standard.
Correction. If the bath has a stability of 2c and the standard is accurate to 1c then the root sum squared should be applied to have a 95% confidence in the standard reading.
This is reason ANSI Z540 suggest that the standard should be in all practical purpose 4 times better than what is being calibrated which is a k factor of 2. Otherwise the uncertainty should be documented on the calibration report.
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Again, a lot of talk and extrapolation and we get all befuddled.
Back to reading the actual requirement(s) ...
I could not find any reference in the FDA CFR requiring the use of an NIST certified thermometer. If someone can find that reference, please post it!
We purchase certified thermometers and use them as our 'standard' to check all other thermometers that are either not formally certified or have past their certification deadline. This is done Quarterly. It's simple ... line them all up in a waterbath (or incubator) just make sure at least one thermometer is indated certified and use that one as the 'correct temperature' to which others are allowed to vary whatever your tolerance is.
btw: Anyone hear that story about why mom cuts the ends of the ham before she cooks it?
Please see this post regarding the requirements of calibrating thermometers.
http://www.bloodbanktalk.com/forum/showthread.php?t=2978&page=2
When calibrating Liquid in glass thermometers a procedure such as NIST monograph 150 should be observed. The working standard should be 4 times more accurate then the unit under test in order to have a confidence factor of 95%. When calibrating using a liquid bath the standard and the UUT tips should be at the same depth to account for the temperature gradients within the bath fluid. In the case with 305mm full immersion thermometers either you must use a bath deep enough or calculate a stem correction to obtain the correct reading. Most cal labs use a fixed mounted scope with a reticle to read the glass thermometers to prevent any parallax and obtain a higher resolution of the reading.
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These need to be done on an annual basis. The only group that has had issue with us (in my former life with a blood center) has been the FDA. We were unable to convince the remainder of the clinical laboratories of this as a matter of good laboratory practice, so we can't borrow throughout the lab. Some facilities buy certified thermometers for the ranges that they use and discard when the calibration "expires". They state that they have found this less expensive than sending out an NIST on an annual basis. The same would apply to stopwatches and timers...
The issue with discarding devices after the calibration expires is that you end up with a unknown whether that device was still in calibration at the time it expired. Even if it was compared to a new device there is a level on confidence (95%) can't be made unless the new device is 4 time more accurate in accordance with ANSI Z540. It is important to continue to have traceability from one device that would be discarded to the replacement device.
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Just wondering how often everyone is getting their NIST thermometer recertified? I can't tell that ours has been done since it was bought long ago. This is the thermometer that we use to check all our other thermometers in-house. Some people are thinking that the certified NIST is good forever, however I feel that is should be recertified at some point.
There are a number of vendors out there that can provide the service. The turn around time is important to most customers. We have been doing a lot in the last 20+ years.
Keep in mind that a glass thermometer will change over time due to the strains in the glass and other factors.
Regards,
John Dozier
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Hi Terri,
Try googling "calibration cap". A calibration cap is a fixed precision resistor that simulates a predetermined temperature. It is very inexpensive, maybe $50, and it's a certified instrument that is UKAS traceable, an international standard equivalent to NIST. If all your thermometers fit this tool, you don't need to send anything back annually. Just buy one cap annually to use with all your thermometers for verification of accuracy that is accepted on an international basis. Pardon - I should say you only need to send those back that don't match the cap's reading within the degree of variation stated for accuracy.
When calibrating digital thermometers either they should be calibrated as a system (meter and probe) or calibrate them separately using the 2 different standards, one for probe and the other for the meter. Calibrating just the meter isn’t sufficient and will lead to errors.
When calibrating Liquid in glass thermometers a procedure such as NIST monograph 150 should be observed. The working standard should be 4 times more accurate then the unit under test in order to have a confidence factor of 95%. When calibrating using a liquid bath the standard and the UUT tips should be at the same depth to account for the temperature gradients within the bath fluid. In the case with 305mm full immersion thermometers either you must use a bath deep enough or calculate a stem correction to obtain the correct reading. Most cal labs use a fixed mounted scope with a reticle to read the glass thermometers to prevent any parallax and obtain a higher resolution of the reading.
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When validating your coolers several things should be considered when testing. The coolers should always be loaded with the same amount of mass. For example if you load the cooler short by 2 units of blood something like a gel pack needs to take up the volume. Secondly you should be testing your coolers in the worst case upper and lower temperatures. Different loading methods should also be observed. Stacking the units differently has a impact on the results. Once you have completed your test then whatever type and brand gel packs are used during the test should be used in the field since some are more dense, etc.
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We have found some manufactures that try to prevent outside calibration companies from calibrating there systems. I one case and I won't mention the manufacture, however they provided the annual calibration and we provided quarterly alarm validations. As a surprise to the blood center a number of there probes were reading incorrectly and this was just days after the manufacture recalibrated the system.
We know that Mack Info Systems doesn't calibrate there own systems, because they believe that it would be a conflict of interest. I am not implying that manufactures would falsify any calibrations, however it certainly is to there advantage to show that there system doesn't drift.
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We had completed a in depth validation study on coolers including boundary testing. If you would like I could see if our customer would be willing to share that information assuming that you are using the same cooler and loading technique.John Dozier
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Cliff,
Thermistors, RTD, Thermocouple, IC sensors are all devices that require a electronics to interprets the change in there outputs. RTD's are the most accurate however if shock i.e. dropped they will change in there resistive output requiring recalibration. They are still the best choice of probe to use. IMO once a qtr. you should do an alarm check and have the system calibrated once a year and if you find that the probe isn't alarming at the correct temperature during your qtr. check, then re-calibrate that probe.
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We provide NIST weight calibrations at our mass lab. Our turnaround time is much quicker than any other calibration labs in the country.
Calibration of weights isn't as simple as placing a weight on a balance and taking a reading. The proper method accepted by NIST is to do a comparison to a known (True Mass which is a calculated value). All the information can be found in the NBS handbook 145. NBS is now known as NIST.
We also provide discounts to blood banks for weight calibrations.
Please visit our website at www.stiservice.com or give us a call.
Always remember the rule of thumb in the metrology industry is that the standard used in a calibration should be when at all possible 4x more accurate then the instrument under test. Even when calibrating thermometers, keep in mind if it is a full immersion type and your unable to immerse completely then a stem temperature correction has to be applied in the calculation.
We also provide Temperature calibrations too. And many other repair/refurbishment services. We also Manufacture the worlds best Tube Sealer and provide the USA in Temp Checks for monitoring temperatures in blood bags.
We work with customers like Ortho Clinical Diagnostic Systems, Chiron, Merck, Astra Zeneca, ARC, New York Blood Center, UBS, the list goes on.
State Technology, Inc.
ISO 9001:2000 registered
510 Heron Drive
Bridgeport, NJ 08014
856-467-8009
fax 856-467-9481
email: emailus@stiservice.com
Regards,
John Dozier
Thermco blood bank thermometer
in Transfusion Services
Posted
If your looking for a 4 point calibration, then you may want to consider having stiservice.com provide the calibration. The standard calibration points provided are 0, 6, 10, 12 C.