The gas mixing application (Sensit.App.GasMixer) is a utility for manually mixing gasses with two Alicat MC-Series Gas Mass Flow Controllers.

User Manual

Hardware

Alicat mass flow controllers use a standard serial port to communicate, and you need two of them (because you're using two mass flow controllers to mix gasses). No other hardware is required.

Theory

To obtain a gas with a desired concentration, sometimes it is desired to mix two gasses together. In this situation, one gas we wish to measure is called the "analyte," and the gas we wish to dilute with is called the "diluent". Using two mass flow controllers, we can control the amount of gas flowing from a bottle of analyte and a bottle of diluent and get the desired concentration with reasonable accuracy.

Connecting to the Mass Flow Controllers

After starting the app, the Serial Ports section will auto-populate with known serial ports on the PC. Select the ports for the mass flow controllers, taking note of which one will control the analyte and which one will control the diluent. Then click the Open radio button. The app will attempt to communicate with the instruments, and will show an error if a mass flow controller is not found, or will enable the mass flow and gas concentration controls if connection succeeds. Clicking the Close radio button will close the serial ports.

Individual Control of Mass Flow

The Mass Flow section of the app operates similarly to the Mass Flow App, except that two controllers are shown. After successful connection to the mass flow controllers, click the Read All button to fetch the current pressure, temperature, volumetric flow, and mass flow from both controllers. Note that the mass flow may not be accurate until the selected gas is correct. Units of measure are not checked. If communication to either device fails, an error message will appear.

Select the desired gas that will be used as analyte and diluent. Click Write Gas to send the settings to the instruments. After setting the gasses, type setpoints for both gasses, then click Write SP to send the setpoints to the instruments. If communication fails, an error message will appear.

Gas Concentration

Set an Analyte Bottle Concentration (used to calculate gas concentration from mass flows and vice versa) (if you want to work in percentages, set the Analyte Bottle Concentration to 100%). Click Read All to read the mass flow from both controllers, calculate the resulting gas concentration and total mass flow, and display them.

To create a gas mix, set the Analyte Bottle Concentration (if you have not already done so), (Total) Mass Flow Setpoint, and Gas Concentration Setpoint, then click Write All. The necessary mass flows for analyte and diluent will be calculated and written to the devices. If communication fails, an error message will appear.

Closing the App

Use the File --> Close menu item or the app's close button to close the serial port (if it is still open) and exit the application. If you're finished mixing gas, don't forget to write the mass flow setpoint to zero first!