Microwave Calibration Program Version 2.0

Peter J. Walter

This program was written to guide the analyst through the calibration of a microwave unit and the conversion of Watts to an instrument's percent power settings for calibrated units. This will allow the transfer of microwave procedures between microwave units and between laboratories.

System Requirements

Get CAL-MW 2.0 (110K)

Installation of CAL-MW.exe

Create one directory and one sub-directory on the computer's hard drive. c:\microwav\ c:\microwav\calibrat\

Copy CAL-MW.exe into directory c:\microwave\

Copy Calibrat.unt, Calibrat.~un, and all data files (*.dt) into directory c:\microwav\calibrat\

This program can be run from MS-DOS or the MS-DOS prompt in windows.

Program Summary

This microwave calibration program is a menu based program which allows one to calibrate a microwave unit and convert Watts to % power. The graphical display of the calibration curve can only be printed on a MS-DOS compatible graphics printer. If you have such a printer, before running the calibration program, run the program that comes with MS-DOS. The program will take a few seconds and only returns a new prompt. This procedure loads a driver that allows the printing of a graphical display. To print the screen press and hold [SHIFT] and [PRINT SCREEN] simultaneously.

When the program first loads there will be an introduction screen. At the first menu one chooses to either calibrate a microwave or recall previous calibration data. When you choose to calibrate the instrument two instructional screens will appear describing the calibration procedure. You will them be asked to make triplicate temperature measurements at 11 different power settings. At the top of each data set the required power setting will be displayed, followed by fields for the mass of water used and the initial and final temperature readings. When all the required measurements are made the calibration data will be displayed in table and graphical format.

There are several demonstration calibration data files to examine before you run an actual calibration.

Calibration Procedure for a Conventional Microwave Digestion System

1. Fill two 2500 mL glass beakers with DI water and let them come to room temperature. (~2 hrs.). Fill squirt bottle with water also.

2. Have four 1-liter Teflon PFA containers and their covers (with ports sealed) clean and at room temperature.

3. Partially disassemble the microwave probes and pull back the temperature and pressure probes in the microwave cavity until they are out of the way of the rotating vessel. Remove the 12-vessel carousel and insert the low platform turntable.

4. Heat 500-1000mL of tap water in a glass beaker for 5 minutes at full power in the microwave unit with the fan on full.

5. Assemble the thermometer (in 0.1 °C and estimable to 0.05) and stirring platform. Have two magnetic stir bars and a pair of Teflon tongs available.

6. Weigh 1000.0 0.2 g into a one-liter container.

7. Measure the temperature of the water to 1/100 of a degree °C while stirring gently. Remove the stir bar.

8. Reweigh the water. Add a drop or two of water, if necessary, to bring the weight back to 1000.0 g. Cover the container taking care not to spill any water.

9. Place the filled container on the turntable near the center post at the start position (marked on the plastic).

10. Program the microwave unit for 2 minutes and 2 seconds at full power (100%). Hit run/on and start the turntable rotation in the reversing mode. Keep fan on full all the time.

11. Remove the container to the stirring platform as soon as the program has terminated.

12. Carefully remove the cover and insert a stir bar. Lower the thermometer into the container near the center.

13. Measure the temperature to 1/100 °C (estimate the second place) while stirring gently. Record the highest reading taken in the first 20-30 seconds.

14. Remove the thermometer and stir bar. Discard the heated water and wipe the thermometer dry. Let the container cool.

15. Repeat the process four more times. The first container should be back to room temperature by the time it's needed again. Remember to refill the empty 2500 mL glass beaker with fresh DI water after the 3rd trial.

16. Repeat the measurement process at 99, 98, 97, 96, 95, 90, 80, 70, 60, 50 and 40% power. There should be 60 measurements in all.

17. Take the calibration measurements and run through the CALIBRATION PROGRAM Peter Walter has written for the microwave.

"Dir for microwave calb prog" 3

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Last Modified Wednesday, May 20 1998
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