0 Preface Operation status: Starting from the start of production, this screw air compressor has frequent braking. When the pressure on the air compressor display is 0.40MPa, the air compressor automatically starts running, but when the pressure rises to 0.78 At MPa, the air compressor enters the no-load operation state. After 90 seconds of no-load operation, the air pressure does not fall below 0.40MPa, and the air compressor enters the shutdown state, but when the pressure drops below 0.56MPa within 90 seconds, the air is empty. The press enters the automatic running state, causing the motor to be in operation for a long time, which has a great influence on the service life of the motor and other components. And because the electric motor car is running in a single machine, this brings a considerable hidden danger to the production of the coke oven. After a period of research, the technicians found that the starting brake of the air compressor is directly related to the pressure sensor on the air compressor.

1 Failure analysis and processing The pressure sensor used in the air compressor is manufactured by the piezoresistive effect, also known as piezoresistive sensor. It is a sensitive device that uses gas pressure to act on the resistance strain gauge to convert the pressure change of the measured gas into an electrical signal. When the stress of the substrate changes, the strain gauges also deform together to make the resistance of the strain gauge. The change occurs, so that the voltage applied to the resistor changes. The strain gauge produced by the strain gauge is usually small when the force is applied. Generally, the strain gauges form a strain bridge and are passed through a subsequent instrumentation amplifier. Amplify and transmit to the processing circuit (usually A/D conversion and CPU of the air compressor PLC) display or actuator, and perform low pressure loading and high pressure unloading on the air compressor.

Through analysis and searching for the cause of the frequent start of braking of the air compressor, it was found that the pressure drop time when the pressure reached 0.78 MPa was too fast, which was lower than the set time of 90 seconds. However, the pressure value displayed on the gas storage tank is the pressure value that is started to the air compressor. After a period of on-site inspection, it is judged that the cause of this phenomenon is due to the position of the pressure sensor, which is found immediately after the rear part. The aftercooler and the aftercooler cool the curved pipeline filled with compressed air by drawing in the cooling air by the fan. During the bending pipeline, there is a certain leakage phenomenon for various reasons, and there is a one-way behind the aftercooler. The valve, which causes the pressure value detected by the pressure sensor to not match the actual value of the gas tank. The pressure value detected by the pressure sensor is only the pressure change value inside the air compressor, so the pressure drop is faster. In addition, the pressure sensor measures the pressure of the inlet gas of the cooler after the air compressor, and the temperature varies widely: 20 ° C ~ +100 ° C. Force sensor of any principle has the effect of temperature on force value drift, there are two kinds of effects: one is the effect of temperature on the zero point of the sensor; the other is temperature versus sensor The impact of the output. The intake pressure sensor adopts the piezoresistive force measurement principle. The resistance value of the bridge formed by the diffusion technique is easy to change with temperature, and the piezoresistive coefficient of the piezoresistive element has a large negative temperature coefficient, which easily causes the resistance value and The temperature coefficient of resistance is discrete, so the piezoresistive pressure sensor is sensitive to temperature, which is ten times or even several times that of resistance strain type: the change of ambient temperature will correspondingly cause the change of four parameters below the pressure sensor. : Change in zero output voltage, output amplitude, pressure sensitivity, and bridge resistance. For example, typical values ​​for these characteristics of the pressure sensor are shown, where the zero and full scale errors are expressed as a percentage of full scale at 25 °C.

Temperature/Celsius Temperature Characteristics of Bridge Resistance and Pressure Sensitivity Air Compressor Operation System Diagram Zero output voltage refers to the output voltage of the bridge without any pressure. The pressure sensitivity refers to the normalization in the constant voltage source power supply mode, the output amplitude, the inverse (down to page 293) SNR (soft threshold wavelet transform) two 24.3354 SNR (hard threshold wavelet transform) two 24.1442 3SNFU soft threshold +5 Point Median Filter) 2 24.7704 SNFU Soft Threshold + 3 Point Median Filter) 2 23.9112 4SNR (3 Point Median Filter + Soft Threshold) = 24.8624 5 Conclusions This paper studies wavelet transform and median filtering and various combinations in the signal go In the effect of noise, we compare and find that the wavelet transform is better than the median filter when the smooth signal is denoised, and the soft threshold is better than the hard threshold. In general, the soft threshold is simple, convenient, effective, and efficient.

From.

2 Actual effect After the above transformation, the air compressor will stop immediately after the air compressor reaches the set stop pressure after the air compressor is running. Since the position of the pressure sensor is changed, the intake pressure sensor is ensured to have a high measurement accuracy in its operating temperature range, ensuring that the detected pressure is consistent with the pressure in the gas tank, and the detected data is actual data. The number of starts and stops of the air compressor is greatly reduced, and the service life is prolonged.

3 Economic analysis before transformation: Due to frequent braking, the service life of this air compressor motor is about 4 months, and the damage to other components is more serious.

After the transformation: reduce the number of starts and brakes, and the life of the air compressor is extended.

Moreover, the time required to inspect an air compressor to affect production is about 2 hours. During this time, about 160 tons of coke can be produced, and the dry quenching steam power generation capacity is 15000 degrees.

Air compressor equipment, although small in size, plays a vital role in production.

It can be seen from the above analysis that the economic benefit brought by the renovation project is about 1 million yuan per year.噶

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