Gas chromatography is a common fault diagnosis

There are many kinds of gas chromatography, and the performance is different. Mainly include two systems. That is gas path system and circuit system.

Gas path system main pressure gauge, purifier, regulator valve, flow regulating valve, rotor flowmeter, six sampling valve, injector, a chromatographic column and detector etc.; electronic systems including the electrical components of the regulated power supply, temperature control device, an amplifying circuit, automatic samples and collecting device, data processor and recording and electronic device.

To analyze and judge the fault of the chromatograph, we must be familiar with the process of gas chromatography, and the two systems, especially the structure and function of these two systems. The fault of the chromatograph is varied, and the cause of the fault is also many, and the method of partial inspection must be adopted, that is to divide the fault. For the gas path system fault, nothing more than is various gases (especially carrier gas) leak phenomenon, gas, gas steady flow is not good, and so on.

For example: baseline if always drift downward, namely "level" value decreases gradually negative, which most likely is the carrier gas leakage, then we must find each part of the joint whether there is leakage phenomenon, if no leakage and baseline drift, may is the failure of the circuit system. Chromatography gas path fault, analysts can identify and eliminate, but to circuit troubleshooting is is not easy, you need to analysis workers have the knowledge of a certain type of electronic circuit, and to clear the host wiring diagram and the system electrical schematic diagram (especially connected graph). In these diagrams clearly painting out of the control unit and the controlled object, the specific marked each connector wire number and the fate of the, according to the diagram to check circuit, fault finding is very convenient.

The fault of the chromatographic system is generally the fault of the temperature control system and the fault of the detection system. Temperature control system (include column temperature, temperature detector, sample thermostat) main return route controllable silicon and a heating wire, wherein, thyristor conduction angle change, change of heating power, and the temperature changes (constant or non constant). And the control of the thyristor conduction angle change is the auxiliary loop (or temperature control circuit), including platinum resistance (thermal components) and linear integrated circuits, etc..

It can be seen from the above, if problems of temperature control system, we must first check SCR is bad, the heating wire is bad (or short), platinum resistance is bad (fault or short circuit or poor contact. Second, check the other electronic components of the auxiliary circuit.. Amplification system common fault is the ion signal line damp or disconnect and high resistance switch (sensitivity) moisture, integrated operational amplifier (such as: AD515JH, OP07, etc.) and the performance of the poor or bad and so on.

HPLC troubleshooting exclude both to do local but also take into account the overall, "fruit" must have "for", to clarify the line, gradually remove the "fruit" (fault) of "because" to narrow the scope of failure.

For example: if the baseline non-stop dithering or baseline noise is large, the first amplifier signal input line is disconnected, observe the baseline, if returned to normal, fault in amplifier and processor (or recorder), and in the gas path part or temperature control unit; on the contrary, it means that fault occurs in amplifier and recorder (or processor) unit. This part of the examination of the fault diagnosis method is very useful in practice.