How to Schedule Mercury-in-Glass Thermometer Calibration

D

darkafar

#1
We have three mercury-in-glass thermometers. We calibrated them before first putting them into use. That was about one year ago. By the suggestion on the calibration certificate issued by an external lab, we should calibrate them once per year.


I’m not fully convinced that we should calibrate fluid-in-glass thermometer once per year. I prefer to calibrate them once for all. I want to see, how other factories schedule their liquid-in-glass thermometer calibration activities.
 
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harry

Super Moderator
#2
Re: Mercury-in-glass thermometer, how to schedule calibration?

We have three mercury-in-glass thermometers. We calibrated them before first putting them into use. That was about one year ago. By the suggestion on the calibration certificate issued by an external lab, we should calibrate them once per year.


I’m not fully convinced that we should calibrate fluid-in-glass thermometer once per year. I prefer to calibrate them once for all. I want to see, how other factories schedule their liquid-in-glass thermometer calibration activities.
I suppose the first question you need to answer is: where you use it, how often and how critical are the readings to your process?
 
D

darkafar

#3
Re: Mercury-in-glass thermometer, how to schedule calibration?

Suppose it is a thermometer to measure warehouse temperature, how do you schedule its calibration?
 

BradM

Staff member
Admin
#4
Re: Mercury-in-glass thermometer, how to schedule calibration?

Scheduling calibration will certainly depend upon other factors. As far as the calibration interval, that is up to your discretion.

I would develop some recommended interval, as mercury can become separated and yield some erratic readings.

It's all about risk and return. You can go out longer than a year, but you risk having more exposure to failure.

Based solely on my opinion and practice, we usually verify them once a year. But note, that's just one user and one practice.
 

harry

Super Moderator
#5
Re: Mercury-in-glass thermometer, how to schedule calibration?

Suppose it is a thermometer to measure warehouse temperature, how do you schedule its calibration?
Unless you have temperature sensitive materials like some type of glue, paint, chemicals, etc. otherwise it shouldn't be a big problem. As one cover posted in another thread, are you interested in knowing whether it is telling the truth?

If needed, can you verify it with another thermometer - preferably a calibrated one used elsewhere. If not, can you compare its reading with another one or two. The logic is not all 2 or 3 can be out in tandem. If the readings are inconsistent (within limits) it is an indication that one or more may be out. Finally, you may want to check the zero degree (ice point) or boiling point. This is what they do with thermometers used for general purpose in the food industry where +/- 1 or 2 degrees is acceptable.
 
P

potdar

#6
Re: Mercury-in-glass thermometer, how to schedule calibration?

We have three mercury-in-glass thermometers. We calibrated them before first putting them into use. That was about one year ago. By the suggestion on the calibration certificate issued by an external lab, we should calibrate them once per year.


I’m not fully convinced that we should calibrate fluid-in-glass thermometer once per year. I prefer to calibrate them once for all. I want to see, how other factories schedule their liquid-in-glass thermometer calibration activities.
Certain equipment are 'calibrated for life'. It depends on where you put them to use and what is the likelihood of them going out of calibration. A fluid in glass thermometer is one such equipment. If you see no reasons for it to go out of calibration where you use it, it is calibrated for life. It will either break or it will continue working ok.

Other such examples are glassware used in a laboratory. A burette or a pipette is calibrated for life if used to measure solutions. The same is not true if it is measuring suspensions. The suspensions may erode the device / cause deposits on it - causing it to go out of calibration.
 
A

amanbhai

#7
Re: How to schedule Mercury-in-Glass Thermometer calibration?

We somehow calculate the amount of kerosen oil in bulk containers & it could easily cost us millions.
We had two options 1. chinese made thermometer was costing very little to us (as much as 10 time less) than the Uk made but the accuracy of both totally different. The UK make is much better so we opted for UK.
Now, as far as the calibration is concerned it is the user who can define next calibration date not the calibration agency.somehow you have to justify that.
Calibration forever of Mercury-in- Glass thermometers........ i don't agree with this idea. I don't understand why?
:thanks:
 

Jerry Eldred

Forum Moderator
Super Moderator
#8
Re: How to schedule Mercury-in-Glass Thermometer calibration?

Although I've long held an INITIAL CALIBRATION ONLY view on liquid-in-glass thermometers, some very knowledgable colleagues over the years have shown me a good reason they need periodic calibration.

A not-too-well-known possibility for error on these thermometers is micro-fracturing inside. A small fracture (or multiple fractures) along the stem WILL cause negative temperature errors. Particularly on the ASTM type.

So if your application requires known accuracy, they definitely need periodic calibration (verification).
 
K

Karl_pmel_ssbb_cqe

#9
Re: How to schedule Mercury-in-Glass Thermometer calibration?

Buy mercury thermometer with auxillary scale at 0C if needed so you can check at ice point.

Have calibrated initially: scale and ice point.

Inspect annually and prepare ice point bath per ASTM method, see change in ice point vs. past calibration. Apply change to scale, and use for this calibration cycle.

This is based on careful examination of thermometer at manufacture and subsequent calibration - i.e., sort out the bad ones.

The ice point shift is explained by the relatively thinner glass in the bulb and the thicker glass in the scale. The scale should have less change than the bulb. The bulb impacts the ice point as most of the mercury is contained in the bulb.

See J. Wise of NIST paper http://ts.nist.gov/MeasurementServices/Calibrations/upload/SP819.PDF
 
F

freelovefest

#10
Re: How to schedule Mercury-in-Glass Thermometer calibration?

ISO is pretty clear about the need to only calibrate mercury thermometers initially and then drop them from the control program. I had always disagreed until I re-read ISO 14969, which is the techinical guide for the 13485 standard. The guidelines are paraphrased below:

"7.6.3 Some monitoring and measuring devices which require initial calibration or certification need not be included in the control programme. Examples of such equipment are
 mercury-in-glass thermometers,
 steel rulers, and
 laboratory volumetric measurement glassware that is not exposed to processes or environments which might affect its calibration.
Monitoring and measuring materials intended to provide a qualitative reference should be stored and maintained in a location which does not compromise the integrity of the material"

If you store your thermometers well, and there are no movable parts to them, this should be a good enough reference to use with any auditor. It certainly changed my thinking on the subject. Still, a good 20 year interval, with this guideline as justification should quell any concerns a regulatory body might have.
 
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