The Environics, Inc. Post
Often, customers come to us looking for a gas flow management system to fit a very particular set of criteria. In some cases, this requires just minor customization of a current Environics model. In other cases, a completely unique design is required. Today, I share with you one interesting example. Although I focus on the first system we designed, we have since made similar systems for other customers whose needs parallel these.
Our customer needed to dilute explosive gases at high concentrations in order to calibrate gas detectors. After working with our sales and engineering teams, we designed and built a modified version of our Series 4040 gas dilution system which included a dual chassis design.
The electronics enclosure includes the power supply and PC boards for controlling the Mass Flow Controllers (MFC) and direct acting solenoid valves in the second enclosure. The electronics enclosure connects to a computer via a 9 pin serial port connector and cable. The 4040 software, on the computer, communicates with the microcomputer board inside the electronics enclosure.
The second enclosure is sealed and houses the MFCs, valves and components to support the enclosure purge. A continuous purge flows through the enclosure while it is running. This serves two purposes. The first is to carry out heat built up by the internal components. The second is to dilute any potential leaks that may develop. The gas plumbing inside this enclosure was vacuum leak tested to 1X10-8 ATM CC/SEC He.
In addition to continuous purge flow, the enclosure is pressurized to approximately 5” H20 while running the enclosure purge. This provides and indicator that the purge is activated as well as preventing any air leaks into the enclosure from outside. A safety vent was added to vent the enclosure to atmosphere if the pressure inside the enclosure reaches 20” H20. This could happen if for some reason the purge vent becomes blocked or the pressure on the purge rotameter is too high.
The two enclosures are connected electrically via two control cables labeled MFCs and VALVES. An earth ground wire is connected from the electronics chassis to the aluminum mounting plate inside the purged enclosure. This safely discharges any static electricity that can build up in a system with flow.
Have a similar need? You can contact us at (860) 872-1111 or here for more information.
Today, we will focus on gas chromatography (or GC), a technique used by many of our existing customers in a wide variety of fields. To state it simply, GC is a method used to separate, identify and quantify chemical compounds. A mobile phase containing the sample is passed over an unmoving and immiscible stationary phase. The mobile phase is comprised of the sample and a carrier gas (typically helium, nitrogen, argon, hydrogen or air). The purity of the carrier is critical and ultra-pure gases are normally purchased or, in the case of air, zero air can be generated on site for cost savings and high purity.
The time in which it takes components in the carrier to pass through the stationary phase, known as the retention time (tR), is determined. The more soluble a component is in the stationary phase, the higher the retention time.
Once a component passes through the stationary phase, a detector allows the user to identify each of them, determine their mass and quantify the concentration. There are a wide variety of detectors, and the detector chosen depends on the components and the needs of the user.
The most commonly used detectors are the flame ionization detector (FID) and the thermal conductivity detector (TCD). They share a common sensitivity and functional concentration range. TCDs can be used to detect virtually any component other than the carrier gas and is non-destructive, while FIDs are sensitive primarily to hydrocarbons and incinerate the entire sample.
Most importantly, proper calibration of the GC is essential. By calibrating GC, the various retention times for compounds of interest are detected. Also, the area under the peak can be used to determine the concentration of the sample components by comparison to a determined calibration curve.
A calibration curve is generated by running various dilutions of the compound/s of interest and then plotting response time and against concentration. These points represent the calibration curve. No two compounds will produce exactly the same calibration curve, and the user must construct a calibration curve for each analyte. It is also best practice to rerun the calibration at frequent intervals. Precise calibration standards can be generated by gas dilution systems, which offer the advantage of on-site gas blending of 100% pure gases cylinders, providing a solution to using numerous, costly premixed cylinders of gas.
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