Sample Thermocouple

Thermocouple Position

Use the Thermocouple Clamp

The thermocouple must be attached to the analyzer prior to running an analysis. There are three possible configurations for the thermocouple:

• inside the sample tube
• inside the sample tube surrounded by a quartz sheath
• outside the sample tube

Best accuracy is obtained when the bare thermocouple is placed inside the sample tube. In some cases, one or more of the gases used during the experiment may react with the thermocouple's Inconel material. A quartz sheath is available to protect the thermocouple when the gases or sample used in the experiment may damage it. In this case, the sheath is placed around the thermocouple and the thermocouple is positioned inside the sample tube. When placed inside the tube, the thermocouple can be adjusted so that the end is in the sample or just above it. Always try to position the end of the thermocouple as close to the furnace thermocouple as possible.

Positioning the thermocouple along the exterior of the sample tube is less accurate than the other configurations. If the thermocouple is placed outside the sample tube, ensure it is clamped against the sample tube, and that the end does not extend below the point where the sample tube begins to taper.

1. Disconnect the analyzer from the power source.
2. Lift the top cover of the analyzer.

3. The valve cover is held in place by two knobs or plungers. Remove the valve cover by pulling the plungers outward until the valve cover is released. Pull the cover up and out.

4. Remove the insulation that surrounds the valve. The thermocouple ports are located toward the front of the block.

Left port - use to place the thermocouple outside the tube Right port - use to place the thermocouple inside the tube Thermocouple connector - disconnect to ensure the thermocouple tube does not get bent

Use the cotton gloves provided in the accessory kit when handling heated surfaces. These cotton gloves are not intended to protect hands when heated surfaces are above 60 °C. If the zone is not near room temperature, loosening or tightening the fittings may damage the analyzer components.

5. Disconnect the thermocouple connector.

6. Use an open-ended wrench to loosen the sample thermocouple fitting.

The sheath is very fragile and can be easily broken. Because the sheath is made of quartz, cotton gloves must be worn when handling the sheath. Oils from fingers may lower the quartz melting point.

7. Adjust the thermocouple:

To change the position:

Loosen the fitting for the plug in the alternate thermocouple opening and remove the plug. Remove the fitting that retains the sample thermocouple. Move the sample thermocouple from its current position to the new position. Place the plug in the unused thermocouple opening and tighten the fitting. Reinstall the sample thermocouple retaining screw. If using the quartz sheath, perform the following before proceeding. The sheath can only be used when the thermocouple is being placed inside the sample tube. Remove the ferrule from the thermocouple, straighten the thermocouple as much as possible. Insert the thermocouple into the sheath. Place a larger ferrule around the sheath.

To adjust the length:

See Determine the length of the thermocouple. Adjust the thermocouple wire up or down as needed.

8. Tighten the thermocouple fitting.
9. Place the insulation in its original position. Reinstall the valve cover.
10. Return the upper front panel and the top panel to their original closed positions.
11. Power ON the analyzer.

Determine the length of the thermocouple

When adjusting the length of the exposed portion, consider the following:

Thermocouple   Recessed area inside furnace End of thermocouple should be below the line marked on the sample tube

• The end of the thermocouple should be aligned as closely as possible with the furnace thermocouple.
• The end of the thermocouple should never be placed outside the painted (black), recessed area inside the furnace.
• If the thermocouple is positioned inside the tube, its end should generally be located approximately 2 to 3 mm (1/8 in.) below the line marked on the sample tube.
• If the thermocouple is positioned outside the tube, its end should not extend below the point where the sample tube begins to taper.

Use the Thermocouple Clamp

If the thermocouple is placed outside the sample tube, a clamp must be used to secure the thermocouple to the sample tube.

Recalibrate the Sample Thermocouple

A calibration file is created specifically for each analyzer before the analyzer is shipped. This calibration file is installed during installation. If the original calibration file is corrupted or missing, or if the sample thermocouple is replaced, recalibration will be needed.

Do not attempt to calibrate anything other than the sample thermocouple without prior approval from a qualified Micromeritics Service Representative.

Prior to recalibration, ensure:

• The analyzer is powered ON and the application is running.
• All heat zones to be calibrated are stabilized at ambient temperature.
• Familiarity with manually controlling the analyzer.
• All gas flows through the analyzer are stopped.
• The furnace is open, and the sample tube is removed (the thermocouple is bare and exposed).
• A traceable thermocouple meter and a water bath (ambient temperature) to immerse the sample thermocouple are available.

1. Go to Unit [n] > Calibration > Calibrate.

2. Place the water bath around the thermocouple so that the lowest 25 mm (1 in.) is immersed in the water. Place the thermocouple meter (reference thermocouple) parallel to the sample thermocouple so that both thermocouples are at the same temperature.
3. After the reference thermocouple meter reading stabilizes, enter the ambient temperature reading in the Low Cal. field on the Instrument Calibration window.
4. Remove the water bath. Move the tip of the reference thermocouple so that it touches the sample thermocouple tip yet allows the furnace to be closed.

5. Go to Unit [n] > Enable Manual Control. Ensure a checkmark displays to the left of the menu item. If the analyzer schematic does not display, go to Unit [n] > Show Instrument Schematic. Set the furnace target temperature to 1000 °C. Use a ramp rate of 50 °C/min. Observe the schematic to ensure that both the furnace temperature and sample temperature are increasing.
6. After the furnace and sample temperature have stabilized, enter the reading from the reference thermocouple in the High Cal. field on the Instrument Calibration window.
7. Use manual control of the furnace to return the temperature to ambient.
8. On the Instrument Calibration window, click Accept to save the new values. Make a backup copy of the settings when prompted.