Although these devices have been miniaturized, they still fundamentally perform the same tasks that the first GC instruments did.
#A diagram of a gas chromatograph software
With digital electronics and software providing the interface between the operator and the device (in this case the inlet heater), we can see that, if the software can be operated through a data system separated from the GC instrument over a company intranet or over the internet, then the instrument can as well.Įven though software provides the user with convenient and powerful controls, the instrument itself still relies on mechanical devices to operate. A second circuit within the inlet block includes a temperature sensor (usually a temperature-sensitive resistor) that provides a signal back to the on board software when the desired temperature is reached so that the heater circuit can be opened (in other words, turned off). Second, the data system transfers the request to the instrument using one of the communication protocols (typically USB or ethernet) where the microprocessor on the instrument receives the signal and, through its on-board software, sends a low-voltage signal to a relay, which closes a mechanical switch to activate the heater. First, you enter the value into the data system (or on the front panel of the instrument if it has a keypad or touch screen). As the user, you want to instruct the instrument to heat the inlet to 250 ☌. Digital control of these analog devices is what allows a gas chromatograph (GC) instrument to be operated from an external data system or even from off-site as long as the requisite software and networking are available.įigure 1 shows the flow of data or instructions between an external control system and an electronic component on a GC instrument, such as the inlet heater. As seen in the September column, the basic controls (valves opening and closing, heaters heating, and switches moving) for data collection and analysis are still analog operations that are performed by mechanical devices even though these devices have been miniaturized. Taking this idea one step further, we see that this computer controls all aspects of instrument operation, including temperature and flow control and valve or switch actuation.
![a diagram of a gas chromatograph a diagram of a gas chromatograph](https://www.theengineeringconcepts.com/wp-content/uploads/2019/02/GAS-CHROMATOGRAPHY_11.jpg)
In our previous column, we explained that the controls for today’s gas chromatographs include an on-board computer that provides the low voltage signals that actuate and direct analog devices that control functions such as starting, stopping, and data collecting (1).
![a diagram of a gas chromatograph a diagram of a gas chromatograph](http://www.organicchem.org/oc2web/lab/exp/subelim/gcdiag.gif)
We see that the same fundamental electronic principles used to manually control gas chromatographs in the 1970s are still at the centre of today’s modern electronically controlled systems. Drawing on classical electronics and instrument designs, we see the evolution of instrument controls from knobs and gauges on the front panel of the instrument to computer control and, finally, to today’s web-based systems that allow instrument control and monitoring from anywhere. This instalment of “GC Connections” is a follow up to September’s column “From Detector to Decision: How Does the GC Instrument Generate Your Data?” This time, we explore the other side of the instrument-data system relationship how the data system controls the functions of the instrument.