Abstract: The instability of infrared carbon-sulfur analyzer detection system directly affects the accuracy of the analysis results of the tested substances. The structural characteristics infrared carbon and sulfur analyzer, it works in combination, from the power supply, an infrared light source, chopped wave motor, several parts of the infrared detector, preamplifier, A / D conversion board unstable factors discussed Analysis , And put forward the ideas to solve the problem, to improve the maintenance efficiency of the instrument has important guiding significance.
1 Summary
Infrared carbon-sulfur analyzer is one of the most important analytical instruments in the metallurgical and mechanical industries . It can quickly 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 operators and maintenance personnel are also relatively high. The analysis and discussion of the influencing factors of the influencing detection system are of great significance to the maintenance of the instrument and equipment and to guarantee the normal development of the scientific research work.
For many years, the instability of infrared carbon and 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 a high-frequency furnace and oxidized by oxygen at a high temperature of the combustion furnace, so that carbon and sulfur in the sample are oxidized to C02, CO, and S02. The generated oxidation product is loaded with oxygen into the sulfur after passing through a dust removal and water removal purification device. The pool measures sulfur, and the mixed gas containing CO2, CO, SO2, and O2 enters the heated catalytic furnace, catalytically converts CO—>CO2, SO2—>SO3 through the catalytic converter, and the mixed gas is introduced into the sulfur removal reagent tube and then introduced into the furnace. The carbon detection cell measures carbon, and the residual gas is discharged outside through the analyzer. The output of the carbon and sulfur detectors was sent to the computer system via pre-amplifier and A/D conversion for data processing, and finally the percentages of carbon and sulfur were obtained.
Analysis of the influencing factors of instability
The measured signal of the substance and the output power value of the detection system, the radiated power of the infrared source, the chopper motor frequency, the infrared light detector, the A/D analog-to-digital converter, and the external disturbance factors all have a great influence on the system. The reason is as follows.
First, the working power
Detection system operating power supply ± 15V, 5.5V, 24V, 5V, it is to ensure the normal operation of the detection system, the preconditions for this part of the circuit work conditions and output values ​​are not normal:
(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.
Second, infrared light source
The infrared radiation emitted by the infrared light source is proportional to the power of the light radiation. The change of the optical radiation power directly affects the change of the signal output size. Such a change will cause the change of the detector's baseline, that is, the presence or size of the 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 ​​of the carbon and sulfur detectors also gradually decrease, and the instrument will alarm when 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 signal output has a very large variation, which is often overlooked.
Third, Libo Motor
The chopper motor modulates the optical signal into a signal with a certain frequency and sends it to the detector. This design is to cleave the infrared light signal into a square wave signal to ensure the stability of the signal after amplification by the circuit. 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 aperture to suddenly flicker, and the detector's received signal fluctuation is even zero.
Fourth, infrared detector
The 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 kept stable to avoid interference with the signal. 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.
V. 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.
Sixth, A/D conversion board
The voltage signal is collected by the 16-to-1 chip, then converted to a digital signal by the A/D chip and sent to the computer for processing. This process is easy to generate interference signals, resulting in the system monitoring window observation working conditions, sample detection integration process and calculation The main reasons are:
(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. 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.
Seven conclusions
Through the analysis of the influencing factors of instability, the signal output value caused by aging and performance degradation of electronic devices is unstable or no output, ripple is large, output signal noise is large, and data collection is missing or missing. Increasing the utilization of equipment plays an important role.
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