Introduced the structural characteristics of the series gas chromatograph and common fault types

First, the main gas path structure characteristics and common fault distribution:

Fault 1: The carrier gas flow rate is low, and the low pressure before the column can be divided according to the steady flow valve:

Before the valve: (1) the air passage is blocked (the large filter direction is reversed, or the resistance is too large);

(2) The instrument carrier gas inlet pressure is too low (two-stage pressure regulator failure);

After the valve: (1) gas path leakage (joint, pressure ring, septum in the injector or gas path);

(2) Blockage at the diverting outlet of the steady flow valve;

(3) The steady flow valve cannot be opened;

Fault 2: Low carrier gas flow rate, abnormally high before and after the column

The fault point does not exist on the gas path and valve in front of the valve. It only exists in the gas path behind the valve. The gas path between the steady flow valve and the detector is blocked, and the gas path between the steady flow valve and the pressure gauge is unblocked.

Fault 3: high carrier gas flow rate, high pressure in front of the column

The fault is distributed on the two-stage pressure regulator and the carrier gas steady flow valve, and the steady flow valve fails.

The most common failure phenomenon of the H2, Air, and capillary supplemental gas systems introduced in the series of gas chromatographs is that the gas velocity is insufficient, resulting in difficulty in FID, FPD flameout or ignition. Since the gas is measured on the ionization base, the fault points are distributed throughout the gas path.

(1) The needle valve cannot be opened (the opening position is incorrect);

(2) The metallurgical powder filter block with the valve plug is blocked;

(3) the valve needle is broken;

(4) The valve seat air hole is blocked (the air resistance is too large);

(5) The ionization base is blocked by the gas path (the gas resistance is too large);

(6) Air leakage (air leakage at the base, valve body, seal ring, and gas line joint).

Second, the detector system structure characteristics and common fault distribution:

TCD fault distribution:

Fault 1: The noise is too loud

(1) hot wire vibration;

(2) The carrier gas flow rate is unstable;

(3) hot wire contamination or oxidation;

(4) pool cavity pollution;

(5) The insulation of the hot wire and the lead wire is reduced.

Fault 2: Drift too much

(1) The carrier gas flow rate of the reference column and the analytical column are unbalanced;

(2) When using Ar as a planting gas, no methane (90% Ar, 10% methane) was added;

(3) The resistance of the hot wire is asymmetrical.

(4) Air leakage from the carrier gas path or the thermal conductivity cell.

Fault 3: Bridge current interruption

(1) TCD hot wire has a broken path;

(2) The sample concentration is too high (signal exceeds 4 minutes);

(3) no carrier gas passes through the thermal conductivity cell;

(4) The hot wire temperature is set to the bottom;

Fault 4: Using nitrogen as a planting gas, when measuring H2 or He component, the H2 peak (He peak) is a W-shaped peak.

(1) The purity of the carrier gas is insufficient (the purity requirement of N2 is >99.998%).

(2) The concentration of H2 or He is too high.

FID fault distribution:

Fault 1: The detector barrel is not tightened or the aluminum gasket is not well sealed;

(1) the pedestal leaks;

(2) probe arm pine;

(3) detector insulator contamination;

(4) Nozzle and probe arm pollution;

(5) H2, Air is not clean;

(6) FID signal cable is loose;

(7) condensate is present at the nozzle or detector base;

(8) The polarization voltage fluctuates greatly and is unstable;

(9) The column loss is large.

Fault 2: Nonlinear at high concentrations (<=107 range

(1) Poor contact between the polarization voltage and the nozzle;

(2) the ignition coil is in contact with the cylinder (causing the polarization voltage to short to the ground);

Fault 3: No response or very small response:

(1) FID stud nut or injection pad leaks;

(2) The nozzle is clogged or the detector leaks;

(3) The signal probe arm is open or the signal cable is broken;

(4) the flame is not ignited;

(5) Capillary injection system septum cleaning gas resistance is too small;

(6) The split ratio is too large during the capillary injection operation;

(7) The FID amplifier range setting is incorrect.

Fault 4: Ignition is difficult:

(1) The ignition coil is disconnected or has poor contact;

(2) The ignition cable is open;

(3) The ignition coil is not in the correct position and is not in the H2 and Air mixed airflow;

(4) The ceramic nozzle hollow screw is blocked;

(5) The low seat air circuit is blocked or leaking seriously;

(6) Hydrogen and air flow are not correct.

ECD general fault phenomenon and distribution:

Fault 1: The fundamental frequency value is too high (the baseline millivolt is too high) to eliminate the cause of air leakage and electronic components after the fault distribution;

(1) Chemical contamination of radioactive source sheets;

(2) The oxygen content in the carrier gas is large, or the deoxidizing filter is ineffective;

(3) The column aging is incomplete and there is column loss;

(4) chemical contamination of the H2 pipeline leading to the ECD base;

(5) The pool current selection switch is not in the correct position;

(6) The signal cable is open.

Fault 2: The base flow value becomes negative:

(1) Chemical contamination of ceramic insulation, there is leakage current;

(2) The source is seriously drained and the source chip is invalid;

Fault 3: Poor stability, serious noise and drift;

(1) The source core or cylinder is not firmly fixed;

(2) The probe arm is loose and cannot be in good contact with the core;

(3) The core and the base are not well sealed;

(4) Air leakage or pollution of the pneumatic system;

(5) The column loss is large;

(6) Radioactive source film contamination.

FPD fault phenomenon distribution:

Fault 1: No fire:

(1) Igniter failure:

(2) H2, Air1#, Air2# gas path is leaking or blocked.

(3) The flow rate is not suitable.

Fault 2: No peak:

(1) Photomultiplier tube damage;

(2) High voltage circuit failure;

(3) The cable connection is incorrect;

(4) The flame is extinguished.

Fault 3: There is no sample peak in the dissolution peak:

(1) Only the inner flame is ignited, the outer flame is extinguished, and the "O" type seal ring on the Air2# base is aging, causing the cylinder to leak;

(2) The column is incorrectly selected;

(3) Air flow (carrier gas, 1# air, 2# air, H2) is not accurate;

(4) the attenuation is too large or the sample concentration is too low;

(5) The filter selection is not suitable.

Fault 4: Sensitivity bottom:

(1) The photomultiplier tube has low gain;

(2) The detector window is dirty;

(3) The flow ratio of each gas path is not accurate.

Fault 5: Interval burrs appear on the baseline:

(1) the column packing particles are vaporized by the flame;

(2) condensation of the outlet water;

Fault 6: The baseline does not return to zero:

(1) no filter is installed;

Fault 7: Drift:

(1) The detector has not reached stability;

(2) The high voltage (gain) is too high;

(3) The gas path is not clean;

(4) The filter fails;

(5) The detector leaks light;

Fault 8: Residual background without flame:

(1) The detector leaks light;

(2) The dark current of the photomultiplier tube is too large.

Common faults and distribution of TSD detectors:

Fault 1: High noise:

(1) The bead is overheated (H2 flow is too large or the bead current is too large);

(2) The bias voltage is incorrect;

(3) The nozzle and the base are not sealed;

(4) the bead is in contact with the nozzle or the collecting net;

(5) Nozzle or bead pollution;

Fault 2: Low response or no response:

(1) The temperature of the bead is too low (bead current is too low);

(2) The bead bias is incorrect (should be -4V);

(3) damage to the bead;

(4) The H2 flow rate is not adjusted to the best sensitive point, and the carrier gas or air flow is incorrect;

(5) The column has adsorption;

(6) Leakage of the cylinder or pneumatic system;

(7) The TCD amplifier range setting is incorrect.

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