Thermoemeter, one point left

I have the draft of a method for calibrating the themoters. Using a Platinum high precision thermometer and iced and boiling baths. I do not have the means to generate a stabe tempeature at any point in betweeen. ASTM says that you must veryfy the thermometer at least at three points covering a least 60% of the thermometer capacity. How bad would it be not to check the middle point?

Awfully bad, since without a third point there is no way for you to know if your scale output is linear, or a curve, which could massively affect your results.
You have three options really

  1. Send your equipment to a professional lab to be calibrated
  2. Purchase a calibrated and validation compliant bath (oil, water, sand or hotblock) to generate your temperature. This should be recalibrated professionally at least yearly.
  3. Finally, the rubbish option, suitable only really for school-science. Use another known state-change setpoint (I can only think of one substance off the top of my head that melts at a fixed temperature between 0 and a 100 and that’s gallium- a really BAD idea in so many ways!).

If you’re doing GMP critical work use only option 1 or 2.

Hope this helps!

it definitely did. Thank you!

Which ASTM standard is this in?

I want ir to add to cparr that leaving a point left on the calibration of a thermometer it’s not awfully bad. Recently we bought some thermometers that came with a certified certificate of calibration and there was only two test points on the calibration. However; I don’t support this practice, and using three point is definitely better.
BTW, the boiling point its very hard to achieve with poorly designed instruments. Good news, you can do something about it.

We figured out the way to do the three points. In case someone is interested this is a cost effective way to calibrate thermometers.
you need a circulating water bath, a standard thermometer, and distilled water ice cubes.

  1. prepare an iced water bath for the 0 degrees check point.
    2 and 3. set you circulating water bath at the desired temperature. Eg: 50 deg C and then 80 deg C.
    We used a Brookfield, and it is stable enough.

Once determined to be operational and meeting the specifications, thermometers should be verified
or calibrated at three temperature points: starting at the 0 degree C [32 degree F] reference point and at two additional points,
approximately equally spaced, maintaining 25 degree C [50 degree F] or less between points. Points should be selected by the user
such that the lowest and highest test points span at least 60 percent of the temperature range used in test.
Reference : NIST

I have a chiller with a working range of 2-8ºC. At what temperature points I have to calibrate the temperature probe of the chiller. I am calibrating at 0 and 20ºC.