The instability of the detection system of infrared carbon-sulfur analyzer directly affects the accuracy of the analysis results of the tested substances. Based on the structural characteristics of infrared carbon-sulfur analyzer, combined with its working principle, it analyzes and discusses the unstable factors from several parts such as working power source, infrared light source, chopper motor, infrared detector, preamplifier and A/D converter board. , And put forward the ideas to solve the problem, to improve the maintenance efficiency of the instrument has important guiding significance.
Infrared carbon-sulfur analyzer is one of the most important analytical instruments in the metallurgical and mechanical industries. It can rapidly analyze carbon and sulfur in solid materials such as steel, iron, copper, alloys, carbon compounds, ore, cement, ceramics, and glass. The detection system is the heart of the carbon-sulfur analyzer. It is very important to ensure the stability of the output (baseline) of the detection system. However, there are many factors that affect the detection system's instability, and the technical requirements for the operation and maintenance personnel are also relatively high. The analysis and discussion of the influencing factors of the influencing detection system is of great significance to the maintenance of the instrument and equipment and to guarantee the normal development of the scientific research work.
For more than 1 years, the instability of infrared carbon-sulfur analyzer detection systems has been a problem that has plagued many users. After a long period of research and exploration, it has accumulated valuable experience in the maintenance of this type of equipment, laying a good foundation for the improvement of equipment utilization, the successful completion of scientific research and production tasks, and the maintenance of infrared carbon and sulfur analyzers.
2 The working principle of the instrument The sample is introduced into the high-frequency furnace and oxidized through the oxygen at the high temperature of the combustion furnace to oxidize the carbon and sulfur in the sample to CO, CO, and SO: the generated oxidation product is passed through the dust removal and water removal purification device. Oxygen is loaded into the sulphur detection cell to determine sulphur. The gas mixture containing CO:, CO, SO: and 0 is brought into the heating catalytic converter, and after the catalytic converter converts CO—c0, s0:s0, the mixed gas passes through In addition to the sulfur reagent tube, a carbon detection cell was introduced to measure carbon, and the residual gas was discharged outside through the analyzer. The output of the carbon and sulfur detectors was sent to the computer system via pre-amplifier, A/D conversion for data processing, and finally the percentages of carbon and sulfur were obtained. Figure 1 shows the block diagram of the infrared carbon-sulfur analyzer.
3 Analysis of the influencing factors of instability The signal of the measured substance and the output power of the working power source in the detection system, the infrared source radiation power, the chopper motor frequency, the infrared light detector, the A/D analog-to-digital converter, and the external disturbance factors The major reasons that affect the system are as follows.
3.1 Working power detection system The working power supply is ±15V, 5.5V, 24V, 5V. It is a prerequisite to ensure the normal operation of the detection system. The reasons for abnormal operation status and output value of this part of the circuit are:
(1) The aging of some devices causes the output value to be unstable and has a large ripple. The normal power output allowable fluctuation range should be within ±10%, if the out of range is considered abnormal.
(2) Some devices have no output or the output waveform is not correct. By comparing the voltage at the main operating point in the measurement circuit with the normal value, the damaged component can be found.
3.2 Infrared light source The infrared radiation emitted by the infrared light source is proportional to the power of the light radiation. The change in optical radiation power directly affects the change in signal output size. Such a change will cause a change in the baseline of the detector, that is, the presence or size of infrared radiation, and the detector baseline will be reflected accordingly. The causes of changes in the infrared light source radiation signal are as follows:
(1) The light source gradually deteriorates, light radiation weakens, and the signal output is low. Baseline output values for carbon and sulfur detectors will also gradually decrease, and the instrument will alarm when it falls below the normal range.
(2) The light source heating wire is broken or de-welded and no signal is output. Measure the light source heating wire resistance value is correct (the correct value is generally about 5Q).
(3) Weak contact of light source heating wire and power plug oxidation cause poor contact. Due to the change of the contact resistance, the output of the signal output changes greatly, which is often overlooked.
3.3 chopper motor chopper motor is to modulate the optical signal to a certain frequency signal sent to the detector, this design is the infrared light signal chopper into a square wave signal, to ensure that the signal through the circuit after the stability of the amplifier. Therefore, the abnormal operation of the motor will cause the detector signal to output little or no output, mainly due to the following reasons:
(1) The chopper motor does not rotate; one is the failure of the working power supply, and the other is the chopper motor rotating shaft is stuck.
(2) As the motor rotates and wears for a long time, the clearance between the sleeves is large, the rotation of the motor blades is not stable, and even the blades hit the wall of the detection pool and are blocked or stuck.
(3) The working frequency of the chopper motor is deviated from the normal value, causing the light passing through the light hole to suddenly flicker, and the detector's received signal fluctuation is even zero.
3.4 Infrared detector Infrared detector is a key component of the gas analyzer. It converts the optical signal into an electrical signal through infrared radiation. Under normal operating conditions, the ambient temperature should be stable to avoid interference signals. The easy situation is:
(1) Device damage No output signal.
(2) The device has low aging sensitivity and large output signal noise.
(3) Device solder joint oxidation, poor solder contact, output signal instability.
3.5 Preamplifier The preamplifier amplifies, filters, and amplifies the weak signal output from the detector. The small changes in each part of the system will cause changes in the amplifier J. The most likely problems are the following.
(1) The performance of the micro signal amplifier is degraded. When checking, the filter capacitor should be mainly concerned and the grounding should be good.
(2) Poor contact between zero potentiometer and gain adjustment potentiometer. After a period of use, turn the potentiometer back and forth several times to ensure good contact.
(3) The amplification of the four-op amp amplifier is reduced, resulting in a lower analysis result. 3.6 A / D converter board voltage signal through 16 to 1 chip for signal acquisition, and then by the A / D chip into digital signals and sent to the computer for processing, this process is easy to produce interference signals, resulting in the system monitoring window to observe the working conditions, The sample detection integration process and calculations are affected, mainly due to:
(1) The aging quality of the A/D converter board deteriorates, causing an increase in interfering signals and disordered digital signals.
(2) The instrument is not well grounded, and external signals interfere with the signal, resulting in missing data.
(3) Poor contact between the A/D converter board and the bus slot results in loss of collected data.
4 Conclusion Through the analysis of the influencing factors of instability, the signal output value caused by aging or degraded electronic devices is unstable or no output, ripple is large, output signal noise is large, and data collection is missing or missing. Solving and improving the utilization of equipment plays an important role.
