FAQ - Thermometers and Probes

Thermometers and Probes

Before you begin entering your measurements, GLOBE asks that you first complete a calibration datasheet. This is a necessary step taken to ensure the accuracy of the thermometer you are using.

In order to print the calibration sheet, visit the GLOBE Teacher's Guide Search Tool. In the search filter use the "Documents and Investigations" drop-down menu and click on Atmosphere -> locate the Protocol Specific Documents -> select the check box for Data Sheets and click the Apply Filter button. Select document titled Digital Max/Min Thermometer Calibration and Reset Data Sheet from the search results.

GLOBE requires five test readings. They can be taken all in one day (at least one hour apart) or over the course of several days, whichever is the most convenient for you.

In order to complete the above sheet, you will need a second thermometer to calibrate with. Here are the specifications for your calibration thermometer:

Instrument Specifications: Calibration Thermometer

The maximum/minimum thermometer will be calibrated with a second thermometer that is an organic, liquid-filled thermometer with a temperature range of -5° C to 50° C. The thermometer must be factory calibrated and tested with standards traceable to N.I.S.T (The National Institute of Standards and Technology - United States) to an accuracy of +0.5° C, with 0.5° C scale divisions. It must be supplied with a metal jacket with holes at the bulb end to allow for circulation, and a hole at the top by which to hang the thermometer in the instrument shelter for calibration of the maximum/minimum thermometer.

Of course, your calibration thermometer will need to be checked for accuracy. This involves putting your thermometer in an ice bath and, after 10 minutes, making sure it reads between -0.5° C and +0.5° C.

Next, visit the GLOBE Teacher's Guide Search Tool In the search filter use the "Documents and Investigations" drop-down menu and click on Atmosphere -> locate the Protocol Specific Documents drop down menu and click on Air Temperature -> select the check box for Protocol and click the Apply Filter button. Choose Maximum, Minimum, and Current Temperature from the results and scroll down to page 5.

Once you have completed checking your calibration thermometer, move the thermometer to your instrument shelter and fill out the calibration data sheet printed earlier.

Instrument Specifications: Digital Max/Min Thermometer

The Digital Max/Min Thermometer used should have either an accuracy of +0.5° C or a precision of at least +0.5° C and an error offset that is temperature independent. These thermometers can either be digital single-day max/min thermometers that are checked and reset each day or digital multi-day max/min thermometers that log temperature values for multiple days. Calibration for these thermometers is not expected, as they have a precision of +0.5° C and a defined error offset that GLOBE is able to reference from the instrument manufacture if need be.

GLOBE no longer needs the thermometer calibration offset itself, simply make sure thta your thermometer falls within tolerance. If not, you'll need to account for the difference manually before reporting your data to GLOBE, or obtain a new instrument. We have a calibration field guide for alcohol and temperature probe thermometers that will work fine with digital max/min thermometers, located at this URL.
The FIRST time you press the Max/Min buttons you will get the highest/lowest temperature over the current 24 hours. Remember, you want to hit the Max/Min button twice to get to the D1 Reading. The D1 reading is the Maximum over the last 24-hour time frame, since the time the reset button was pressed. That's why it is so important to make sure that you hit your reset button during your solar noon. But timing is everything! If you read your thermometer before the time of your reset (if you reset it at 12:10 and you take a reading at 12:05), you will be reading the CURRENT 24-hour period. The thermometer will not update the data until 12:10.

First, click on the "Enter Data" link on the home page, or go to "GLOBE Data" tab on http://www.globe.gov, then select Data Entry from the menu. Click on Live Data Entry -> Expand the organization, then select the site and click on the edit site button on the right side of the page. In the site definition page, select the Atmosphere site type check box, then select the thermometer type Digital Multi-Day Max/Min. Once you select the thermometer type, Reset date link will show up. Click on it and enter the date of reset. Now you can add a note in the comments that you reset the thermometer.

In order to find out the date of last time your thermometer was reset, in the Data Entry page, under the Atmosphere site, click on Multi-Day Soil and Air Temperature New Observation data entry form. Once you open the form, you will see the last thermometer reset data.

GLOBE allows digital probes to be used to measure:

  • Temperature (soil, air, and water)
  • pH
  • Barometric Pressure
  • Relative Humidity
  • Conductivity
  • Dissolved Oxygen
The probes must meet the specs given in the instrument specifications section of the Teacher's Guide Toolkit. The specifications for hydrology probes have yet to be written; however, we know that probes manufactured by Pasco and Vernier do meet GLOBE specifications.
Replace your thermometer with a digital model. Never use a uTube / mercury thermometer for recording maximum and minimum air temperatures.  It has been determined that this type of thermometer is dangerous due to the mercury it contains. Use a digital maximum/minimum thermometer for maximum and minimum air temperature measurements.
If the current air temperature does not read the same for both mercury columns, then one or both of the sliding scales needs to be adjusted. Both columns need to agree with the green fluid-filled calibration thermometer placed in the instrument shelter with the max/min thermometer. According to the manufacturer, the green fluid-filled calibration thermometer will only give accurate reading when removed from the protective metal cover. The calibration thermometer, minus the metal cover, should be hung next to the max/min thermometer in the shelter. The max/min thermometer can be calibrated by loosening the screw in the back. This will allow the scales to slide up and down. If, after an adjustment, the thermometer still reads incorrectly, then the thermometer should be replaced. Be certain that both types of thermometers (max/min and calibration) do not have fluid separation in the columns.