At present, some advanced centrifuges abroad have become a high-tech comprehensive technology product. There is still a big gap in this area in China. It is necessary to increase the technical content of domestically produced centrifuges and strive to develop products with independent intellectual property rights. There is a lot of work to be done in this area. As a kind of mechatronics equipment, centrifuge has been widely used in hospital inspection, biological laboratory, bio-pharmaceutical, sewage treatment, traditional Chinese medicine pharmaceutical and beverage production. It has penetrated into scientific research, production and other fields.
Feed additive refers to a small amount or trace substance added in the process of feed production, processing and use. It is used in feed in small amount but plays a significant role. Feed additive is an inevitable raw material in modern feed industry. It has obvious effects on strengthening the nutritional value of basic feed, improving animal production performance, ensuring animal health, saving feed cost and improving the quality of animal products.
Classification
1. Bile acid
2. Acidifier
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Selection of drive motor
Commonly used motors are DC motors and AC motors. The characteristics of the DC motor and the AC motor are as follows.
1) Characteristics of DC motors. The structure is complicated, the cost is high, and it needs frequent maintenance (replacement of the brush). Because there is a spark at the brush, it is generally not used in places where explosion protection is required. However, the DC motor speed control circuit is simple, the cost is low, and the speed regulation performance is superior. At present, the performance of the brushless DC motor has matured. In the low power DC motor, a brushless DC motor has been widely used instead of the ordinary DC motor.
2) Characteristics of AC variable frequency motor. The utility model has the advantages of simple structure, low cost, reliable work and low noise. To obtain excellent control performance, variable frequency speed regulation must be adopted, the speed control controller is complicated, and the cost is high. Since the centrifuge can be equipped with rotors of various speeds, the design of the variable frequency motor for driving the centrifuge should be considered for the low speed and large capacity rotor, so that the motor works in the constant torque working area, and the small capacity high speed rotor can be designed in the variable frequency motor. Constant power working area, which can reduce the design power of the variable frequency motor and save costs.
Because the DC speed control circuit is simple and the control performance is superior, the DC speed control cost in the low power system is relatively low. Therefore, the DC speed regulation is still widely used in the small power simple type centrifuge. In order to improve the reliability of the centrifuge drive, the motor spindle should be used to directly drive the centrifuge rotor. At the same time, the special requirements of the centrifuge installation and the damping system of the whole machine are considered. The motor of the centrifuge generally requires special design in the form of the spindle and the shape of the casing. To meet the special requirements of centrifuge drives. If a belt drive or other variable speed drive mechanism is used, a general standard series of motors can be used, but the reliability of the drive is relatively reduced.
Speed ​​control system
DC speed regulation
(1) There are two main types of main circuit DC speed regulation: 1 thyristor rectifier circuit voltage regulation. 2 DC pulse width modulation voltage regulation. The characteristics of the two DC speed control circuits are compared as follows.
1) Pulse width modulation speed regulation. The input DC adopts diode bridge rectification with high power factor and high modulation frequency. The general working frequency is set at around 20 kHz. Due to the high frequency, outside the human hearing range, not only can the noise be reduced, but also the volume of the filter inductor can be reduced. . At present, a variety of pulse width modulation waveform generator integrated circuits are available, and the control circuit is simple. However, power devices use controllable electronic devices such as GTR, MOSFETs, and IGBTs. The overload capability of these devices is relatively low, the trigger drive circuit is required to be high, the front and rear edges of the trigger pulse are steep, and there is a fast overcurrent protection circuit. At present, a variety of intelligent dedicated drive integrated circuits have been introduced, which have various automatic protections. Function, which creates favorable conditions for the wide application of DC pulse width control systems.
2) Thyristor rectification speed regulation. Thyristor overload is very strong and reliable. This is one of the reasons why the thyristor DC speed regulation still has vitality. The waveform distortion caused by the change of the conduction angle of the thyristor reduces the power factor of the rectification, especially when the conduction angle is small, the higher harmonic component is large, the current ripple component is large, and a large smoothing reactor is required. When three-phase controllable rectification is used, the three-phase transformer phase shift synchronization is required, and the three-way trigger pulse forming circuit has a complicated control circuit. At present, a variety of integrated phase shifting flip-flops are available at home and abroad to improve circuit reliability. Fully controlled bridge rectification improves commutator sparks.
(2) In order to obtain good speed regulation performance, the control system generally adopts a double closed loop control system with speed feedback and current feedback. The double closed loop control system has an analog control mode and a digital control mode. Table 1 shows the characteristics of analog and digital control methods.
It can be seen from Table 1 that the digital control method has many advantages, and it can realize various parameters of digital quantity setting, and various protection functions are centrally managed. The state can be easily adjusted by modifying the software, the control is flexible, and the performance is greatly improved.
In the analog control system, when the system speed performance requirements are relatively high, in addition to the speed negative feedback and current cutoff negative feedback double closed loop control, a given delay integral circuit must be added as the soft start circuit. Increase the current and speed differential correction link to control the rate of acceleration of current and speed. This is very effective in reducing the speed overshoot and starting current surge. The reasonable design of the parameters can make the whole speed control system achieve perfect dynamic and static performance.
(3) Selection of sensors in DC speed control system In the DC double closed-loop speed control system, speed sensor and current sensor must be used. The quality of the sensor directly affects the speed regulation accuracy. The advantages and disadvantages of several sensors are compared below.
1) Speed ​​sensor
It can be seen from Table 2 that the speed measuring generator is inconvenient to install due to its large size, and its signal must be converted by A/D before it can be used by a computer, so it is rarely used at present. Photoelectric speed measurement and Hall element speed measurement output is pulse digital signal, and its signal is convenient for computer processing. For example, it is used in analog system. Now there is a dedicated frequency conversion voltage integrated circuit for selection or single-stable trigger conversion, which is very convenient.
2) Current sensor Current sensor generally uses current transformer or photoelectric coupling sensor. The characteristics are shown in Table 3.
It can be seen from Table 3 that since the optocoupler transformer and the Hall-type transformer have a small volume and a fast response speed, they have gradually replaced the traditional current transformer. For some power devices requiring fast overcurrent protection, the common one is The response speed of the transformer often cannot keep up, and the high-speed optocoupler must be used as the current sensor to meet the requirements. Hall current transformers can be used for high power systems, and optocouplers can be used as current sensors for low power systems.
2. The AC variable frequency speed control inverter develops in the direction of large capacity and high performance. Its price performance can be compared with DC drag, and the trend of gradually replacing the DC drive system with variable frequency speed regulation has been formed.
At present, the quality of the inverter is stable, the parameters are convenient and flexible, the functions are increasing, the performance is getting better and the price is decreasing. There are various new inverters with slip compensation, vector control and direct closed-loop control. If the quality of the inverter product is directly used as the speed control power supply of the centrifuge, the performance reliability of the centrifuge machine can be greatly improved.
Since the centrifuge is a large inertia load, whether it is DC speed regulation or AC speed regulation, it should consider taking braking measures during shutdown to speed up the downtime of the centrifuge and improve the working efficiency of the centrifuge.
Refrigeration electrical control
1. Refrigeration electrical control method
(1) Switching control Switching control has two modes, one is contact control mode and the other is non-contact control mode.
1) The contact control mode is controlled by a relay or a contactor. The characteristic of this kind of circuit is that the life of the suction contact is limited, and it is easy to generate high frequency spark to interfere with the electronic circuit.
2) The non-contact control mode is a solid-state relay with photoelectric isolation zero-crossing trigger, which has stable starting, no spark interference and contact life.
The disadvantage of the switch control is that the compressor can be restarted after being stopped for more than 1 minute, and the temperature control accuracy is low.
(2) Frequency conversion control Due to the development of frequency conversion speed regulation technology, inverter refrigeration compressors have appeared. The continuity of the variable frequency control can greatly improve the temperature control accuracy, but the cost will increase if a frequency converter is added.
2. Selection of temperature sensor The temperature control range of the refrigerated centrifuge is generally -10 ~ +40 °C. The working range of the temperature sensor must meet the above temperature range. Since the centrifuge chamber is relatively humid, it is best to use the packaged, installed and exchanged. Convenient, sensor with moisture-proof structure. A variety of temperature sensors, such as thermal resistance type, integrated circuit type (semiconductor type), thermocouple type and thermistor type, are available.
3. Problems that must be paid attention to when designing the refrigeration electrical control system In the switch-type control system, after the compressor is stopped, the compressor cannot be restarted immediately because the pressure at both ends of the internal high and low pressure is not balanced. Therefore, it is necessary to design a delay start circuit after shutdown, and block the start circuit within a certain period of time after the stop to prevent the compressor from being burned repeatedly.
In the switching control system, the temperature is the hysteresis control. Generally, the operational amplifier is designed as a hysteresis amplifier with positive voltage feedback, and the appropriate positive feedback amount is calculated to meet the temperature difference range. Measures should be taken during circuit design to prevent positive feedback from forming oscillations. When the temperature sensor converts the temperature into an electrical signal, the amount of change is generally small. When amplifying the temperature signal, an amplifying circuit with deep negative feedback must be used, and the influence of the temperature drift of the amplifier itself on the temperature measurement accuracy should be considered.
The application of PLC and man-machine interface in the centrifuge control technology PLC has high anti-interference performance, and the communication connection with the touch screen man-machine interface is very convenient. At present, some small PLCs such as Siemens S7-200 series 224XP have analog input and output on the CPU main module. The analog input can be used as temperature signal input. The analog output can be used to control the output frequency of the inverter. The speed of the centrifuge. The pulse signal of the speed is input from the high-speed counting input of the PLC, which can measure the speed and close the speed. At present, some small PLCs have built-in PID control functions, which can easily realize high-precision speed closed-loop control. Touch screen and PLC communication can display the working parameters of the centrifuge, and monitor the door cover, imbalance and automatic rotor identification of the centrifuge. display. Through the touch screen, the inflection point, the lifting speed time, the temperature compensation and the like can be arbitrarily set for the speed reduction of the centrifuge, and the trouble of modifying the parameters by using the single-chip microcomputer to modify the program is overcome. In addition, the touch screen man-machine interface can set the login password to prevent improper operation of unauthorized persons, and can realize the curve display of the operating parameters and the data communication of the host computer to collect data. The user manual's documentation can also be stored on the touchpad for easy access.
The development direction of centrifuge control technology
At present, centrifuges have gradually developed towards intelligent, automated and integrated support. The application of the computer on the centrifuge allows for the storage of dozens of centrifuge parameter setting programs. The fully sealed touch button cooperates with the liquid crystal display to realize menu setting and measurement display, and can display setting parameters and actual running time parameters at the same time, and can conveniently use the Chinese menu to realize man-machine dialogue and convenient use. Automatically record data such as quality control and production operating conditions, automatically generate reports, and obtain data from each batch of processed samples at any time from the computer to monitor the entire processing of the samples. It is also possible to form a complete centrifugal network with other centrifuges through a central control computer, so that the entire production process is under computer control.
The intelligence of the centrifuge is also reflected in the ability to automatically identify the various rotors. Automatically identify whether the rotor is in place, the speed setting is reasonable, and alert the operator. It can effectively avoid accidents caused by inadvertent operation. It can realize the automatic calculation of the centrifugal force according to the rotor model and the rotational speed or directly input the centrifugal force to obtain the corresponding rotational speed. The automatic setting means that the operating speed and acceleration and deceleration time of the centrifuge are automatically set according to the rotor type of the automatically recognized centrifuge. Password protection for the set program. The centrifugation process is controlled by an integrator to ensure that the sample is subjected to the same centrifugal force in different batches.
The direct drive technology of variable frequency speed regulation and brushless DC motor has been gradually used in the drive system. In the aspect of temperature control, the high-efficiency cooling system with fluorine-free refrigeration and the special heating system have been alternately operated to maximize the temperature accuracy and prevent sample freezing and frost deposition. Some advanced centrifuge products abroad have successfully applied semiconductor refrigeration (or heating), which makes the centrifuge temperature control technology enter a new technical application field.
It can promote fat digestion and absorption, protect liver and gallbladder, improve livestock and poultry health and improve feed utilization.
Including citric acid, fumaric acid, lactic acid, acetic acid, hydrochloric acid, phosphoric acid and compound acidifier. Adding an appropriate amount of acidification Qi to the pig diet can significantly improve the daily gain of pigs and reduce the feeding cost.
Including olaquindox, pig fast growth, fast fertility, blood polypeptide, liver residue, animal music, fat pig Wang, etc.
6. Trace elements
Including copper, iron, zinc, cobalt, manganese, iodine, selenium, calcium and phosphorus, which can regulate body metabolism, promote growth and development, enhance disease resistance and improve feed utilization. The daily gain of postnatal pigs can generally be increased by 10% - 20% and the feed cost can be reduced by 8% - 10%,
7. Vitamins
It includes vitamins A, D2, e, K3, B1, D3, B2, B6 and C, as well as a variety of vitamins, choline, pig premix additives, vitafat, Ted vita-80, French fat, health care element, strong element, etc. it can be scientifically selected and used according to different pig varieties and different growth and development stages.
8. Amino acids
It includes 18 kinds of amino acids such as lysine, methionine and glutamic acid, as well as Shengbao, livestock treasure, feed yeast, feather powder, earthworm powder, feeding music, etc. the most used additives are lysine and methionine. Adding 0.2% lysine to the diet can increase the daily gain of pigs by about 10%.
9. Antibiotics
Gold toxin, salinomycin, tetracycline, Bacillin, lincomycin, Kangtai feed additive, zhubao, Baosheng, etc.
10. Insect repellent health care
Including anbaoqiujing, keqiu powder, aibao-34, etc.
11. Mildew proof
Due to the high oil content of rice bran, fish meal and other refined feeds, they are easy to oxidize and deteriorate after long storage time. Adding ethoxyquinoline can prevent feed oxidation, and adding propionic acid and sodium propionate can prevent feed mildew. The addition of cinnamon powder not only has strong bactericidal effect, but also attracts food, flavors, and promotes growth.
12. Chinese herbal medicine
Including garlic, wormwood powder, pine needle powder, mirabilite, Codonopsis pilosula leaves, Maifan stone, wild hawthorn, orange peel powder, acanthopanax senticosus, Atractylodes, motherwort, etc,
13. Buffer feed
Including sodium bicarbonate, calcium carbonate, magnesium oxide, calcium phosphate, etc.
14. Seasonability
Including sodium glutamate, edible sodium chloride, citric acid, lactose, maltose, hay, etc.
15. Hormones
Including raw milk record, promoter, yufeiling, etc.