Mass Flow Controller Calibration

Gas Charts

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 such a device.

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 a Soap Bubble Burette or Other Type of Flow Meter

  These instructions are for assembling and using a burette obtained from Micromeritics. If using another type of flow meter, follow the meter manufacturer’s assembly and operation instructions.
  1. Carefully unwrap the glass tube and the rubber bulb.
  2. Attach one end of the flexible tubing to the side arm of the glass tube.
  3. Attach the metal tubing provided with the bubble burette to the other end of the flexible tubing.
  1. Exhaust port
  2. Flexible tubing
  3. Bulb filled with leak detector
  1. Locate the exhaust port that corresponds to the MFC to be used for this calibration.
  2. Remove external plumbing from that port and attach the bubble burette using the connector provided with the burette. The soap bubble burette must be held in an upright position. For example, if using the Carrier Flow Controller, attach the bubble burette to the carrier gas exhaust port.
  3. Attach the bulb to the bottom of the glass tube.

Determine the Gas Flow Constant for Individual Gases

  1. 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.
  2. Flow the gas to be calibrated through the Carrier gas MFC and sample tube.
  3. Connect a flow meter to the exhaust and measure the actual flow rate. If using a bubble burette, 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.
  4. Go to Unit [n] > Gas Flow Calibration.
  5. Select the gas being flowed.
  1. In Actual flow field, enter the actual flow rate to compute the mass flow constant.
  2. Click Accept to change the Mass flow constant field in the Adsorptive Properties for the gas to the computed value.