Programmable Gas Mixer
The GSM-3 Programmable Gas Mixture takes up to three input gasses and produces user-defined mixtures using these gasses. Up to four different mix programs can be defined and stored at any one time. These mixtures are stored in non-volatile memory, so they don't have to be re-entered the next time the instrument is used. The GSM-3 uses high-accuracy mass flow controllers (MFC's) to set the flow for each gas channel.
Each mixture is defined by a Total Flow, and the percent concentration of each gas in the mixture. The resulting flow for each gas, in ml/min, is computed and displayed on the LCD display. Any of the four stored mixture programs can be selected and run (or stopped) with a pushbutton press. Although the GSM-3 can be operated solely with the front-panel controls, it is most efficiently controlled by the supplied GSM-Comm software (see below).
Because the GSM-3 is suitable for such a wide range of applications, we customize each unit with the most appropriate flow controllers for the intended application.
A remote control software application is supplied with the GSM-3 Gas Mixer. This software runs on any version of Windows, and allows user-defined timed sequences to be created. These sequences automatically switch between any of the four pre-programmed mixtures at specified intervals. These sequences can run once and stop, or repeat indefinitely. This capability eliminates the need to manually switch gas mixtures to follow a particular experimental protocol. These timed sequences can be named, stored, and repeated as needed. Sequencer setup is shown in the image below. Each step in the sequence is programmed with a TIME (in hours, minutes, and seconds), and a FUNCTION selected from a drop-down menu (Mix 1, Mix 2, Mix 3, Mix 4, REPEAT, STOP, or NONE).
The image below shows the main GSM-Comm screen. With the exception of the Sequencer (described above), the mixture parameters are defined exactly as they would be from the front panel controls of the GSM-3. Each mixture (MIX 1 - MIX 4) has a selected Gas, Total Flow and individual gas concentrations. Error checking and reporting prevents the user from attempting to set up an invalid mixture. Any set of programmed mixtures can be named, saved, and retrieved for later use.
Most applications use one or two active gasses (eg. O2 or CO2) and a background gas (usually N2). This background, or Fill gas is selected by the user and is automatically computed to make up the balance of the gas mixture. For example, if the user sets the mixture to be 20.9% O2 and 5.0% CO2, the Fill gas will automatically be set to 74.1%. This insures that the mixture always equals 100%.
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