How to solve common faults in electromechanical control of automatic sampling system

Large-scale sample preparation and analysis equipment such as automatic sampling stations and X-ray fluorescence analyzers have become the standard configuration for online quality control of the cement industry. The automatic sampling system introduced by a cement company can continuously obtain online samples at a final reduction ratio of 1:106 during use, and automatically transfer the samples to the analysis room 100 meters away, instead of manual sampling. The sample station has a strong representative sampling feature, which fundamentally eliminates the drawbacks of manual sampling, but because the system is a typical mechatronic device, the degree of automation is high, there are many components, and any one component is not working properly. This may result in equipment downtime, initial operation and partial installation and manufacturing defects, resulting in multiple shutdowns.
1 Introduction to the automatic sampling station system:
       When the grinding system is started, the sampling screw conveyor rotates in the reverse direction, and the residual materials remaining in the conveyor are returned to the grinding system. After 30 seconds, the machine runs forward and starts to continuously sample the sampling station. All the samples are reduced. The machine is divided into 1:10 or ≤1:10 shrinkage ratio and then mixed into the mixer to achieve homogenization. When the set sampling time is reached, the control gate is automatically opened, and the sampling spoon is moved to the right and will be fixed. The volume (about 150g) of the sample is transferred into the sample cylinder located in the sample holder, and the excess sample enters the returning device. The material in the returning device will accumulate and the material level will gradually rise. When it comes into contact with the rotary material. After the position meter, the returning ash fan is started, and the material in the returning device is blown back to the grinding system. The sample tube is automatically controlled by a set of pneumatic mechanical devices, and the sample tube (cannonball) is automatically completed after the action of the buckle cover and the steering. Under the blow of the conveying fan, it is sent to the receiving station 100 meters away. After the receiving station takes out the sample, it sucks it back to the sampling station. The sample tube returns to the initial receiving position, and the cycle is repeated to complete the sampling function. Executed by 1 SIMATIC 50 small programmable controller control is completed.
2 Common faults and solutions in the self-control part:
2.1 The level gauge is out of control
In the process of use, due to the system is not tightly sealed, when the ash return fan is running, the system has a positive pressure, and some sample powder is sprayed, resulting in an increase in the ambient dust concentration. Dust is easy to break into the level gauge, causing the level gauge contact to malfunction. The return ash fan sometimes runs continuously. Sometimes the fan should start to perform the soot blowing operation but it does not run because there is no signal, causing the returner. Excessive accumulation of ash, until entering the reducer and then into the mixer, and finally cause the mixer to overload, so that the overcurrent protection switch loses its protective effect, causing multiple failures of burning the motor. After the internal contact of the cleaning level gauge has improved, but it can not continue to work reliably for a long time, and the fault occurs again. Then, the output lead of the material level gauge is disconnected, and 2 time is added to the control circuit of the returning ash fan. For the relay, one is set to 25min as the timing when the fan is stopped, and the other is set to 5min as the time for the fan to run after starting the fan, which is cycled twice per hour. In this way, after the abnormal operation of the level gauge is cancelled, relying on the punctual action of the time relay, the returning ash fan can blow off the accumulated ash in the returning device at a time to ensure the operation of the equipment.

2.2 Mixer control gate out of control
The mixer control gate is opened on time when the preset sampling time is reached, and the sample is shrunk and homogenized. The control gate is a pneumatic shutter, and the control mechanism is controlled by an electromagnetic pneumatic valve. The switch position of the valve has a proximity switch induction to transmit the signal to the PLC. However, since the actuator often cannot be opened and closed smoothly, when the device should be opened but not opened, the upstream device continues to operate, and the original program design fails. This condition is included in the interlock, which often causes too much material accumulation in the mixer, and eventually causes the mixer motor to burn out. Considering that the original program is provided by foreign companies, the data in the program part is lacking, and the procedure of adding and modifying has certain difficulties. In view of this, a small 8-point input and output SIEMENTS small LOGO programmable controller is provided, and a proximity switch is added to the switch position of the shutter to realize another road monitoring parallel to the original program controller. When the situation is opened, the interlocking sampling screw conveyor contactor controls the coil to power off the sampling screw conveyor motor to protect the safety of the equipment under abnormal operating conditions.

2.3 The perfection of the sample cylinder clamping sleeve
The clamping sleeve has the function of clamping the sample cylinder to complete the lifting, swinging arm swinging, buckle capping, etc. The clamping sleeve material is made of styrene-butadiene rubber and natural rubber. After 1 year of operation, The clamping sleeve works under the pressure of 0.8MPa, the bearing pressure is high, and the expansion deformation of the clamping sleeve is serious. Especially in the case of low temperature in winter, the material of the clamping sleeve becomes hard and loses elasticity, and the sample cylinder cannot be clamped. The action cannot be performed. In order to alleviate the problem of hardening of the clamping sleeve in winter, the methods of heating by far-infrared lamp and heating by electric heating are used respectively, but the heating is not uniform, but the electrical components such as switches near the clamping sleeve are greatly threatened, which increases the fire. And other unsafe factors. After several tests, 100W wire is wound around the outer wall of the clamping sleeve and a temperature sensor is added to achieve constant temperature control of 60~70 °C. During the winding process, the insulation and flame retardant of the resistance wire should be strictly observed. After modification, the physical ductility of the rubber of the clamping sleeve has changed, and the elasticity is enhanced, which solves the contradiction of the sampling station stopping due to the abnormal working of the clamping sleeve in winter.
In order to ensure the normal operation of the sampling station, in addition to improving the main problems of the above self-control parts, the mechanical components such as the ash return pipe, sample tube, fan pipe, transmission pipe and check valve are also adjusted and modified to make it perfect.