Application of ultrasonic sensor in material level detection of stacker
1. Principle of hammer contact detection
The material level detection of the stacker originally used the long and short hammer contact detection device, its working principle is: when the stacker automatically cloth, if the long hammer contact the material, will produce a switching signal and sent to the site PLC, PLC to the stacker material height has reached the requirements and execute the next action, namely rotation 3. Signal to continue piling. If the material meets the short material hammer, stop the upstream incoming belt conveyor and stacker, and send an alarm.
2. Principle and selection of ultrasonic sensor
2.1 Working Principle
Ultrasonic sensors are developed by using the characteristics of ultrasonic waves. The probe is mainly composed of shell, piezoelectric wafer, damping block, protective film, pre-circuit and output circuit, etc., in the probe is also equipped with temperature compensation element and amplifier circuit, to compensate for the signal deviation caused by the change of environmental temperature, improve the measurement accuracy. Ultrasonic wave is produced by piezoelectric wafer vibration under voltage excitation. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good quadrature (beam).
The piezoelectric wafer in the ultrasonic probe can both transmit and receive ultrasonic waves. When a voltage is applied to a piezoelectric wafer, mechanical deformation occurs as the voltage and frequency change. Conversely, when mechanical deformation is applied to the piezoelectric wafer, an electrical signal is generated. Using this principle, when an electrical signal is applied to a vibrator consisting of two piezoelectric wafers or one piezoelectric wafer and a metal sheet, ultrasonic waves are emitted as a result of bending vibrations. In contrast, when ultrasonic vibrations are applied to the two piezoelectric wafer elements, an electrical signal is generated. Based on these principles, piezoelectric wafers can be used as ultrasonic sensors. Distance or position can be calculated by using the time it takes for sound waves to travel between the sensor and the object.
2.2 Application Selection
In the ultrasonic selection, after multiple comparison and consultation, the final selection of Germany Plus-Plus (P+F) company's model UC6000-30GM-E6R2-V15 double switch point output ultrasonic sensor. The characteristics and working parameters of the sensor are as follows:
1) It comes with a four-pin temperature/setting plug, which can be inserted in four different positions respectively, convenient and rapid setting on site. Where A1 and A2 are setting switching points, E2 / E3 are setting working modes, and T is temperature compensation.
2) The setting process is displayed by the LED light of the sensor body.
3) With ambient temperature compensation function.
4) Double switch point output, RS232 interface
5) Detection range: 350 ~ 6000mm; Transducer frequency: 65kH; Operating voltage: 10 ~ 30V DC, no-load current ≤50mA.
3. Scheme design and debugging application
3.1 Scheme Design
Based on the original design control principle, that is, when the long material hammer is contacted, a switch signal is output to PLC to control the rotation of the stacker 3. Continue piling, when contact with the short hammer output a switch signal to PLC, jump upstream incoming belt and stacker. Therefore, two detection points with different distances should be found to replace the contact position of the original length and length of the material hammer, and the selected ultrasonic sensor can detect between 350 and 6000mm. Therefore, A1 and A2 detection points should be selected respectively within this range, and the distance between the probe 0 OA1 and OA2 should replace the length and length of the original detection device. Set OA1= 1.2m, OA2= 0.8m. When the sensor detects point A1, the dynamic contact action corresponding to point A1 will control the rotation of the stacker 3. Continue piling. When A2 point is detected, the dynamic contact action corresponding to A2 point jumps to stop the upstream incoming belt and the stacker.
3.2 Debugging Applications
3.2.1 Setting Process
1) Set the switch point
Cut off the power supply; Unplug the temperature/setting plug; Power on again; The big arm of the stacker is fixed on the place about lm above the limestone pile, and the ultrasonic sensor is lifted to the position about 1.2m away from the detection object (limestone) by hand. At this time, the corresponding indicator state is double LED green flashing, and the corresponding LED1 yellow light is also blinking. At this time, if the temperature/setting plug is inserted to position A1, Then A1 point setting is completed; Similarly, drop the ultrasonic sensor to a position about 0.8m away from the limestone for A2 point setting. Finally, insert the temperature/setting plug in position T, and the sensor enters the normal setting mode.
2) Set output function
Cut off the power supply; Unplug the temperature/setting plug; Re-energize; Insert the temperature/setting plug into E2 / E3 position, and check the corresponding LED indicator state, namely the output working mode. If the current output mode needs to be changed, you can switch between the three working modes by repeatedly inserting and removing the temperature/setting plug. Here, the switching point mode is set as the green light of double LED and the yellow light of LED1.
Finally, insert the temperature/setting plug into the T position, and the setting process is over. The sensor enters the normal working mode.
At this point, the setting process of ultrasonic sensor is completed, and the sensor probe is fixed at the front end of the stacker arm.
3.2.2 Electrical Cables
Wiring from the field control cabinet to the ultrasonic sensor, and in the cabinet wiring. In order to prevent the detection device from being damaged again when the stacker power cable is short-circuited, it is decided to supply 220V power directly from the isolation transformer to the switching power supply. Since the sensor needs to be powered off several times during debugging, an air switch is added for easy reset. Among them, KA1 and KA2 dynamic auxiliary contacts are the contact signals sent to the PLC control cabinet at the site, and the connection is still according to the original length of the hammer signal.
4. Effect and experience
The ultrasonic sensor is installed and put into operation. Firstly, the automatic operation on site is carried out. The design meets the original process control requirements and the operation is normal. After the conversion to the automatic operation of the central control, the work has been normal. During debugging, note the following:
1) When setting switch point l and 2, the temperature/setting plug shall be inserted into position T after the setting of each switch point to ensure that the switch point enters the normal working mode.
2) If you do not save the current setting or switch the setting function, power off, unplug and restart.
3) After setting the required output mode, insert the temperature/setting plug into T position within 5 minutes, otherwise the temperature compensation function will be lost.
4) If the synchronization function is not required, the synchronization input should be grounded (ov).
5) The installation position of the probe should be as far as possible to avoid large stones scattered to prevent misoperation.
