Calibrating Tzero

The DSC Tzero* calibration requires two experiments. The first experiment is done without samples or pans (baseline); the second is performed with large (approximately 95 mg) sapphire disks (without pans) on both the sample and reference positions. Both experiments use the same method beginning with a cell preheat followed by an equilibration at an initial temperature, holding isothermal for 5 minutes, heating at constant rate to a final temperature and holding isothermal for 5 minutes. The range of temperatures should be at least as broad as the desired experimental range. Tzero calibration should be done at relatively high heating rates such as 20°C/min in order to obtain the most accurate calibration of the sensor thermal capacitance and resistance values. Rates of less than 10°C/min are not recommended for Tzero calibration.

Tzero calibration is only used with the DSC Q2000/Q1000 and Q200/Q100 for Heat Flow T4 and T4P.

NOTE: The "heat flow" signal should be selected and used to measure the heat of fusion or enthalpy of sharp melting transitions such as obtained with Indium.

* Tzero™ describes proprietary technology invented by Robert Danley of TA Instruments-Waters LLC and patented by TA Instruments-Waters LLC (U.S. Patent No. 6,431,747).

Basic Instructions

Follow these basic instructions for baseline slope and offset calibration. Click the links to jump to the specific instructions for that item.

1. Gathering Tzero Calibration Data, which requires two experiments—one run without samples or pans and one run with sapphire disks on the reference and sample positions (without pans). You can do this one of several ways:

• Automatically using the Platinum™ functions. (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Manually using the templates, or custom methods.

• Step-by-step using the Calibration Wizard.

2. Analyze the data. You can do this one of several ways:

• Automatically using the Platinum functions. (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Automatically by defining Post Test Actions (can be applied to templates). (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Manually by specifying the appropriate file then analyzing the data using Calibrate/Analysis (where you specify the desired analysis limits).

• Step-by-step using the Calibration Wizard.

3. Choose from optional Platinum functions:

• Scheduling the calibration sequence (either created through Platinum or your own custom method).

• Enabling run and sequence messaging.

• Print out the .emf calibration file for your records. This file is created after automatic calibration and placed in the same folder used for your data files. It will be named for the sample name entered: e.g., samplename.emf.

Gathering Tzero Calibration Data

Tzero calibration can be performed by setting up the experiments manually using the Experimental View or automatically using the calibration wizard. The calibration wizard method is the recommended procedure since it will step you through all the necessary steps to collect and analyze the data.

You can gather data one of two ways:

• Automatically using the Platinum functions. (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Manually using the templates, or custom methods.

• Step-by-step using the Calibration Wizard.

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Manually Determining Tzero Calibration (Using the Template)

This calibration requires two experiments—one run without samples or pans and one run with sapphire disks on the reference and sample positions (without pans). A general procedure for Tzero calibration is given below.

1. Remove any pans from the cell and cover the cell.

2. Check that your purge gas is connected and set to the desired flow rate. If you are using an RCS or LNCS, be sure a Base purge gas is also used.

3. Select Experiment View and access the Summary Page, then set the instrument to calibration mode using the Mode Selection drop-down list.

4. Select either "Tzero Heat Only Cal"  or "Tzero Heat/Cool Cal" from the Test list.

"Heat only calibration" is used when you are interested measuring transitions or heat capacity while heating the sample.

The "Heat and Cool calibration" is used when you are interested in both heating and cooling data when measuring transitions or heat capacity (this option takes longer to calibrate).

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5. Enter the requested sample information, including the exact Sample Size (zero) and Pan Type (none).

6. For  Autosamplers only: Select the Pan number and Reference number.

7. Click on the Procedure tab. Enter the requested test parameters.

• Lower Temperature & Upper Temperature: Calibration must be performed using the same atmosphere and cooling accessory that will be used in subsequent experiments. Obviously, the lower and upper temperatures chosen for calibration must be within the operating range of the cooling accessory selected. In addition, the temperature range for calibration should be at least as broad as the range that will be used in subsequent experiments on your samples. Typical temperature ranges are: -180 to 400 °C for the LNCS, -90 to 550°C for the RCS90, -40 to 400°C for the RCS40, and 50 to 400 °C for the FACS. See also: Introducing the DSC Cooling Accessories. NOTE: The quench cooler cannot be used for Tzero calibration and experimentation.

• Ramp Rate: Calibration can be performed for heating only or for heating and cooling. The minimum ramp rate is 10°C/min in order to obtain reliable values for sensor thermal capacitance and resistance. Lower ramp rates provide weaker signals and less accuracy. For heat-only calibration, a ramp rate of 20°C/min is recommended. For heat and cool calibration, a rate of 10°C/min may be more practical since it may not be possible to maintain a higher cooling rate down to the lowest temperature of interest. Obviously, the type of cooling accessory determines the maximum cooling rate and minimum temperature for calibration.

8. Click on the Notes tab. Enter/verify the requested information. If an MFC is installed, set the desired flow rate. Calibration should be performed using the same purge gas and flow rate as that which will be used in subsequent experiments on your materials.

9. Click on the Apply button to save the experimental and sample parameters entered for this run.

10. Select Append. Enter the weights of the sample and reference sapphire disks.

11. If more than one run is in the sequence list, schedule the first Tzero run. (An arrow will appear next to the run number in the Sequence Pane for the scheduled run.)

12. Select Start to begin the calibration run.

13. If your DSC does not have an Autosampler, wait until the run is complete then set up the next experiment.

14. Perform the two experiments:  one run without samples or pans and one run with sapphire disks on the reference and sample positions (without pans). Once both runs are complete, analyze the data. See Analyzing DSC Tzero Calibration Data.

15. Save the calibration results by clicking the Accept button (or by selecting Analyze/Accept results from the Calibration menu). This will update the current temperature parameters with this calibration data.

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Analyzing Tzero Calibration Data

Once the calibration run is complete, you can analyze the data using one of the following techniques:

• Automatically using the Platinum functions. (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Automatically by defining Post Test Actions (can be applied to templates). (These functions are available for Q2000/Q200 instruments only and are recommended for first time calibration.)

• Manually by specifying the appropriate file then analyzing the data using Calibrate/Analysis (where you specify the desired analysis limits).

• Step-by-step using the Calibration Wizard.

Automatic Analysis Using Post Run Actions

NOTE:  These functions are available for Q2000/Q200 instruments only.

This method utilizes Post Run Actions to automatically analyze and send the results to the instrument. These are defined while setting up the run sequence and executed at the end of each test.

1. Set up the calibration run sequence manually as described above.

2. Right click on the second Tzero calibration run number on the Sequence Pane to display the pop-up menu. Select Post Run Action.

3. Select one of the following:

• IF NOT -- Successful Tzero Calibration -- STOP. (This will stop the sequence if the Tzero calibration fails.)

• DO -- Tzero Calibration. (This will begin the next run after performing Tzero calibration, with no dependency on the outcome.)

• IF -- Successful Tzero Calibration -- GO next sequence. (This will start the standard run sequence after successful completion of Tzero calibration.)

4. Select OK when finished.

5. Select Start to begin the calibration run. To view or print the Tzero calibration results, see the Calibration report.

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