Mass Flow Controller Calibration
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The analyzer uses a Mass Flow Controller (MFC) to control the flow of gases. The MFC requires a conversion constant for each gas or gas mixture to compensate for variations in gas flows resulting from variations in the gas properties.
In most cases, the default MFC conversion constant yields accurate data. A new conversion constant may be used if:
- A unique gas mixture is used
- The gas to be used is not included in the table
- A higher precision calibration of the MFC for a given gas is required
- Unexpected analysis data lead you to believe that the default value is in error
Flow Measurement
An external device that measures the flow of gas from the analyzer’s exhaust is used during MFC calibration. A soap bubble burette is shipped with the analyzer. For even more precise calibration, use another type of flow meter and follow these instructions for obtaining a new conversion constant, substituting your flow meter for the soap bubble burette.
Install the Soap Bubble Burette
The equipment images in this document may differ slightly from your equipment, however the instructions are the same unless otherwise noted. |
These instructions are for assembling and using the burette supplied by Micromeritics. If using another type of flow meter, follow the meter manufacturer’s assembly and operation instructions. |
- Carefully unwrap the glass tube and the rubber bulb.
- Attach one end of the flexible tubing to the side arm of the glass tube.
- Attach the metal tubing provided with the bubble burette to the other end of the flexible tubing.
- Locate the exhaust port that corresponds to the MFC to be used for this calibration. Remove external plumbing from that port and attach the bubble burette using the connector provided with the burette. For example, if using the Carrier Flow Controller, attach the bubble burette to the carrier gas exhaust port.
- Fill the rubber bulb with the contents of the 8 oz. bottle of the leak detector fluid included in the accessory kit.
- Attach the bulb to the bottom of the glass tube.
The soap bubble burette must be held in an upright position. |
Determine the Gas Flow Constant for Individual Gases
Unit [n] > Gas Flow Calibration
- 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. Flow the gas to be calibrated through the Carrier gas MFC and sample tube.
- Connect a flow meter to the exhaust and measure the actual flow rate. If using the bubble burette shipped with the analyzer, observe a bubble as it rises through the glass tube. The lines on the glass tube indicate the beginning and ending points for measuring the progress of a bubble through the tube. Use a stopwatch to measure the amount of time that elapses from the moment the bubble passes the lower mark on the tube until the moment it passes the higher mark on the tube.
- Go to Unit [n] > Gas Flow Calibration and select the gas being flowed.
- Enter the actual flow rate in the Actual flow field to compute the mass flow constant.
- Click Accept to change the Mass flow constant field in the Adsorptive Properties for the gas to the computed value.
- Attach the gas to be calibrated to an inlet port for the MFC to be used during calibration.
- On the analyzer schematic, right click the Flow Controller icon. Select Set Flow Rate, then enter the flow rate. Click OK.
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