 Frequently Asked Questions |
How do partial and total immersion thermometers differ?
The main difference between partial and total immersion thermometers is the method in which they are calibrated and how they are used. Thermometers calibrated for total immersion indicate accurate temperature when the thermometer is immersed to the liquid level in the capillary. For example, when thermometers measure atmospheric temperature, semi-solids, or liquids, the thermometer is immersed up to the tip or meniscus of the liquid column. Simply put, immerse the thermometer to the temperature point you are trying to measure.
Thermometers calibrated for partial immersion indicate accurate temperatures when the thermometers are immersed to specific depths such as 76mm immersion. Partial immersion is appropriate for any application where total immersion is impractical or impossible, as in a shallow water bath.
Can I use a total immersion thermometer in a partial immersion application or vice versa?
Yes, but it is not practical. If total immersion thermometers are used at partial immersion depths (or vice versa), inaccuracies will occur. These inaccuracies increase as the temperature increases about ambient. Temperature readings can be as much as 5 or 10 degrees “off”. If, in a rare case, you must use a partial immersion thermometer in a total immersion application, corrections for emergent stem must be obtained to achieve an accurate reading. To reduce errors, use the correct thermometer to meet your application requirements.
If the liquid in the column of a thermometer is separated, is the thermometer faulty?
Absolutely not! Any glass thermometer, regardless of type (e.g. mercury-filled, spirit-filled, etc.) can naturally be subjected to separations in the liquid column. This may be a result of improper shipping and handling, or as a result of improper storage. A thermometer can go through several “hands” once it leaves the factory. Therefore, if it is improperly stored or roughly handled, there is the chance that the thermometer liquid will separate. However, you may receive a thermometer in good condition and over extended use it may develop a separation. This may be a result of improper storage. Most thermometers are stored horizontally, usually in a drawer. Over time, this can lead to a separation in the liquid column. It is best to store thermometers vertically (in an upright position) or at an angle of at least 15° or more. Use a special tray or rack to store thermometers properly. Such tools are very inexpensive and will help to eliminate liquid separation in thermometers. Two simple methods have been developed to reunite separated fluid in a thermometer column. If employed correctly, the reunited liquid column will be as good as new.
NOTE: We suggest you wear safety glasses and gloves when working with glass instruments.
Cooling Method
Prepare a solution of shaved ice and salt OR CO2 (Dry Ice) and alcohol. Place the thermometer bulb only in the solution. Keep the thermometer upright. Allow the liquid column to retreat into the bulb, swing the thermometer (bulb down) in an arc forcing the entrapped gas above the column. Allow the thermometer to warm slowly in an upright position.
Heating Method
Heat the thermometer bulb in an upright position away from your face in warm liquid, air, or over a soft flame enough to allow the liquid column to rise slowly until the separated portion of the column enters the expansion chamber at the top of the thermometer. Note that over-filling the expansion chamber will break the thermometer. Tap the thermometer gently in an upright position allowing the gas separating the column to rise above the column. Allow the thermometer to cool slowly in an upright position.
What is the difference between a “calibrated” and a “certified” thermometer?
It is common for the words calibrated and certified to be used interchangeably. All thermometers are calibrated but not all thermometers are certified. In order to manufacture a thermometer, the instrument must be calibrated against a reference standard. Calibration during manufacturing establishes the guidelines for line and number placement on the glass.
If a thermometer is certified, this means that after the instrument is manufactured, it is once again individually calibrated against a reference standard at a specific point or points along the scale. The results of this special second calibration are recorded on an official report from the manufacturer. This report, or certification document, accompanies the certified instrument when purchased.
What is the difference between a Statement of Accuracy and a Calibration Certificate?
All thermometers are calibrated when manufactured. This initial calibration establishes the guidelines for the scale placement.
Statement of Accuracy:
Enviro-Safe®, Easy-Read®, Double-Safe ™ and FRIO-Temp® thermometers are supplied with a statement of accuracy which shows that these thermometers were calibrated against a reference standard traceable to NIST (National Institute of Standards and Technology). This calibration shows that the thermometer has a scale error/tolerance is within ±1 to 2 scale divisions (depending on its range) over the entire length of the thermometer scale. There is no expiration date on this report since a properly manufactured thermometer will maintain its given accuracy as long as it is stored, handled, and utilized correctly. Since individual temperature points are not tested, this is NOT a certified instrument.
Calibration Certificate:
Some applications require that certain thermometers be calibrated at distinct temperature points. This is done AFTER the thermometer is already manufactured. These thermometers are tested against NIST and DKD standards and a scale error is given at those temperature points showing the uncertainty of the measurement to one-tenth of the smallest division. A laminated Report of Calibration is supplied with every certified instrument stating this information. Since thermometers are certified according to NIST and DKD standards, it is recommended that they be re-certified annually in order to comply with ISO 9000, Quality Control or any guidelines and regulations set forth.
Do I need to re-calibrate my FRIO-Temp® thermometer?
The answer is no! Glass thermometers have an internal liquid that is hermetically sealed and that volume cannot change without breakage. Once this instrument is manufactured to exacting standards there will be little if any change in the hysteretic of the glass in the range from 0°C to 100°C, for example, therefore, little or no change in the accuracy of your thermometers. With thermometers manufactured to read high temperatures (over 100°C) there can be a change in the glass bulb, which can change the accuracy over time. This is not the case with your thermometers purchased from H-B Instrument Company! We use the finest glass for both capillary and bulb, which resist change under normal usage. Abuse can cause separation of the liquid column, but this condition can be corrected by reuniting the liquid column.
It is safe to state that the accuracy, after manufacture of our thermometers with scale divisions of 1/2°C or greater, will be the same for the life of the instrument. (See NIST Special Publication 250-23) Therefore we can guarantee the accuracy of your thermometers manufactured by us to be consistent for the life of the instrument. Be assured that no other manufacturer can claim anything better than this! We are and have been in frequent contact with NIST on this issue, and we agree with paragraph 10.0 to 10.2.
An ice point reading is advised periodically, which will prove this statement.
Ice Point Procedure: Simply crush some clean ice, place it in a dewar flask and, as it begins to melt, the resulting temperature is extremely close to 0°C. One can check this “ice point” over time to check for “drift”. We estimate that any drift that may occur will not be noticeable to the normal user of this instrument. Drift of 0.01°C, for example, would be hard, if not impossible to the naked eye, to read on this instrument. The reason we issue a certificate of traceability and statement of accuracy for these thermometers, is to protect customers from the illusion that thermometers must be recalibrated periodically. Recalibration is performed for wide range fractional degree thermometers where accuracy of fractional degrees is critical and where tolerance of 0.1°C or more is required. Most recalibrations are performed to conform to ISO 9000 or other criteria a user may impose.
Why would I want to re-calibrate my thermometer?
There are several reasons why you would want to re-calibrate a thermometer. Here are just a few:
1. There is a need to know how accurately a thermometer is reading or if it is still accurate to specifications.
2. ISO 9000, Quality Control, etc…regulations require Reports of Calibration for thermometers.
3. There is a need to know, for an application, what the thermometer is reading to a high degree of accuracy or between divisions.
4. Reports of Calibration with corrections allow one to calibrate or check other thermometers within certain tolerances.
5. NIST issued Good Measurement Practices 11 for the Assignment and Adjustment of Calibration Intervals for Laboratory Standards. Click here to download.
What are the different types of liquids used in thermometers?
1. Mercury – Metal, molecular formula: Hg, an odorless, silvery liquid with a metallic luster.
2. Mineral Spirits – Petroleum hydrocarbon, clear odorless liquid with a petroleum odor, usually mixed with blue, red or green colored disazo dye.
3. Enviro-Safe® liquid – A mixture of biodegradable citrus liquid and a green, non-toxic dye (Monoazo-Anthroquinone Dye).
4. Mercury/Gallium – Mercury and Gallium amalgam which increases the temperature range by lowering the mercury boiling point (used in thermometers up to 620°C).
5. Mercury/Thallium – Mercury and Thallium amalgam which lowers the temperature range of mercury to below –40°C by lowering the solidification point of mercury.
How safe are Enviro-Safe Thermometers?
The liquid inside an Enviro-Safe thermometer has been certified environmentally friendly by EnviroKleen™. Enviro-Safe liquid consists of a mixture of biodegradable citrus oil and a green, non-toxic dye. The liquid is non-hazardous and is considered extremely safe in any working environment. This eliminates dangers for the user and eliminates any disposal concerns. Check the Material Safety Data Sheet for complete details. There is no thermometer like this anywhere!
How long is:
203 mm?
203 mm = 8” in length 305 mm?
305 mm = 12” in length
405 mm?
405 mm = 16” in length
These are the most common lengths for thermometers.
You can easily convert mm to inches and vice versa using the following formula:
To convert inches to mm, multiply total inches by 25.4 (8” x 25.4 = 203.2 mm)
To convert mm to inches, divide total mm by 25.4 (203 mm / 25.4 = 7.99”)
What is an ASTM Thermometer?
ASTM stands for the American Society for Testing and Materials. ASTM is an independent, private organization that establishes and publishes standards for use in industry. ASTM established thermometer standards suited for special applications. Thermometers are assigned ASTM numbers according to the specifications. Thermometers designed for specific tests may also be useful in various other applications. Therefore, it is possible to purchase an ASTM thermometer for your specific application although it was designed for another application. ASTM thermometers are manufactured to rigid standards.
NOTE: The ASTM Precision series are designed for universal applications. They are certified at five points and a Report of Calibration from the manufacturer accompanies each thermometer.
What is Teflon? Why is it used to coat thermometers?
Teflon is a special material developed by E.I. Dupont de Nemours Company. Teflon coating involves encapsulating a thermometer within a thin layer of Teflon. Since the material is transparent when applied, you are still able to read the thermometer scale and liquid column. The main purpose of Teflon coating is safety. Once a thermometer is coated it becomes less sensitive to breakage. In the event that the thermometer does break, the liquid in the thermometer is contained within the Teflon. This reduces the chance of a hazardous spill if the liquid inside the thermometer is mercury. Teflon also prevents contamination by broken glass.
Does Teflon coating affect the accuracy of a thermometer?
Teflon coating does not affect the accuracy of a thermometer. But Teflon may slow the response time of the liquid column to reach equilibrium temperature. Therefore, Teflon-coated thermometers are not recommended for applications involving timed tests.
Which thermometers can be Teflon coated?
Any glass thermometer can be Teflon coated provided its range does not exceed 260°C.
How do you convert °C to °F and vice versa?
You can use these two formulas to convert any temperature:
°F = 9/5 °C + 32
°C = 5/9 (°F - 32)
There is an error on my 3750 Digital Thermometer that is not listed?
If "LLL" appears:
a. ...if the temperature of the probe is lower than the listed minimum temperature of the unit (in this case, lower than -50°C)
b. ...if the probe is damaged or if there is a poor connection due to corrosion, dirt, etc.
c. ...if there is an open ciruit to the sensor, for example, sensor not plugged in properly
If "HHH" appears:
a. ...if the temperature of the probe is higher than the listed maximum temperature of the unit (in this case, above 200°C)
b. ...if the probe is damaged or if there is a poor connection due to corrosion, dirt, etc.
c. ...if there is an open ciruit to the sensor, for example, sensor not plugged in properly
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