Abstract: Through the study of weighting materials, a mathematical model was established to determine the separation particle size of the centrifuge when separating weighting materials. A variable frequency fully automatic closed-loop control system was designed. Based on the changes in the viscosity and density of the drilling fluid and the load torque and vibration of the centrifuge during operation, the data was collected in real time and fed back to the microcontroller. The collected data was judged by the C++ program written in the microcontroller, and the control system issued corresponding processing instructions, outputting the frequency converter frequency and the flow rate of the slurry pump, so as to achieve the purpose of most effective separation of weighting materials as the drilling fluid properties and centrifuge parameters change. As a drilling fluid solids control device, the centrifuge plays a very important role in drilling operations. On the one hand, it can remove the solid phase of non-weighting drilling fluid, and on the other hand, it can separate weighting materials from weighting drilling fluid [1]. However, the operation of the centrifuge is affected by many parameters, such as: drum speed and torque, screw conveyor speed and torque, drilling fluid feed rate, drilling fluid properties, drilling fluid dilution degree, solid phase content in the liquid, polymer residue degree, etc. Changing any of these parameters will affect the centrifuge's separation effect. Furthermore, power outages and potential technical malfunctions will endanger the centrifuge's safety. I. Determination of Centrifuge Particle Size for Separating Weighting Materials The proposed solution is to use two centrifuges together. The first centrifuge, an adjustable-speed centrifuge with a pre-set separation particle size, is used to separate the weighting material. The second centrifuge is used to remove harmful solid phases [2]. The particle size determination process is as follows: when all particles with a diameter of dc (separation particle size) are separated, i.e., the separation efficiency ET = 1, the settling time required for particles larger than dc is less than the settling time tc for particles with a diameter of dc, while the settling time required for particles smaller than dc is greater than tc. Therefore, the number of particles that can settle from d1 (the smallest particle size in the weighting material) to dc is determined by the ratio tc/tx, while particles from dc to dm (the largest particle size in the weighting material) settle 100%. In equation (2), a is the distribution characteristic coefficient, corresponding to the particle size value when the separation efficiency is 50%. The total separation efficiency is: As shown in Table 1, as the separation particle size of the centrifuge decreases, the separation rate of the centrifuge weighted material increases, but the content of useless solid phase in the separated weighted material also increases. After passing through the vibrating screen, based on the relationship between the weighted material and the rock cuttings, and considering that the solid particles below 33 μm in the hard strata are 81.9% [3], the separation particle size of the centrifuge is determined to be 20 μm, at which point the separation efficiency of the weighted material reaches more than 80%. II. Design of the fully automatic closed-loop control system for separating weighted materials 1. Centrifuge working system Design an automatic detection and control system that can optimize the centrifuge operation and ensure the safe operation of the centrifuge. The motor 46 drives the pump 44 to transport the drilling fluid in the tank 40 through the pipe 42, flow meter 48, density meter 50 and viscometer 52 into the centrifuge for processing. The protection switch 38a is connected to the connector 38. If the gearbox operates under over-torque, the protection switch 38a will cut off the power supply and stop the motor. The operating modes of the centrifuge's screw conveyor and drum in this system are as follows: ① Rotation of the drum by the variable frequency drive 54 → AC motor 24 → belt 26 → hollow shaft 21 → flange shaft → centrifuge 10. ② Rotation of the screw conveyor by the variable frequency drive 56 → AC motor 34 → sun gear 35 → planetary gearbox 32 → flange shaft 19. 2. Single-chip microcomputer detection and control system The centrifuge working system uses two variable frequency drives. In order to coordinate these two variable frequency drives with the liquid supply and obtain satisfactory separation effect, a single-chip microcomputer automatic control system is adopted. In addition, the single-chip microcomputer can also monitor other working parameters of the centrifuge. The monitoring interface of the centrifuge is as follows: (1) The two input interfaces of the single-chip microcomputer 60 are connected to the variable frequency drives 54 and 56 respectively, changing the working frequency of the motors 24 and 34, thereby changing the speed and torque of the centrifuge drum and screw conveyor respectively. (2) The protection switch 38a is connected to one input port of the microcontroller and can respond to the over-torque of the gearbox 32 to protect the centrifuge. (3) One port of the microcontroller is connected to the flow meter 48 to measure the flow rate of the drilling fluid flowing into the centrifuge through the pipe 42. (4) One port of the microcontroller is connected to the densitometer 50 to measure the density of the drilling fluid flowing into the centrifuge through the pipe 42. (5) One port of the microcontroller is connected to the viscometer 52 to measure the viscosity of the drilling fluid flowing into the centrifuge through the pipe 42. (6) One port of the microcontroller is connected to the valve 42a to control the size of the valve 42a opening, thereby controlling the flow rate into the centrifuge. (7) The vibration detector 62 is installed on the outer shell of the drum and connected to the microcontroller 60. When the vibration limit is approached or exceeded, the microcontroller will output relevant instructions to control the frequency converters 54 and 56 to change the operating conditions of the motors 24 and 34, or stop the motors to turn off the centrifuge. (8) Each bearing housing is equipped with a pair of acceleration sensors (one vertical and one horizontal) to detect the vibration of the shaft. When a special signal or parameter appears, it indicates that there is a potential danger, and the microcontroller will issue a warning or take certain control measures. 3. Functions of the control system (1) Through the fully automatic closed-loop intelligent control system, the centrifuge is always in safe operation to efficiently separate the weighted material. (2) When the centrifuge is in normal working condition, the microcontroller outputs the drilling fluid processing volume Q and the main and auxiliary motor speed n based on the drilling fluid viscosity value collected by the sensor. (3) When the centrifuge approaches the limit conditions (limit speed, limit torque, limit vibration, limit current), the microcontroller will issue a warning signal and issue relevant instructions to change the motor operating conditions and the liquid supply of the feed pump to avoid or delay the occurrence of the fault. (4) If the centrifuge has exceeded the limit, the microcontroller will stop the centrifuge to prevent unnecessary damage to the centrifuge. III. Working Principle of Fully Automatic Closed-Loop Control System (1) Use pins p1.2, p1.3, and p1.4 of the microcontroller as input terminals for flow rate Q, density ρ, and viscosity μ (after A/D conversion), respectively; use pins p0.1, p0.2, and p0.3 as input terminals for vibration k, acceleration a, and torque m (after A/D conversion), respectively; use pins p0.5 and p2.6 as output terminals for controlling the drive frequency converter and changing the speed of the main and auxiliary motors, respectively; use pin p2.7 as the output terminal for controlling the valve and changing the flow rate of the feed pump. (2) For the microcontroller chip, use C++ programming language to program different torque signals m, viscosity μ, vibration parameters k, and acceleration a in segments. (3) Use drilling fluid density sensor, drilling fluid viscosity sensor, vibration sensor, acceleration sensor, and torque sensor to measure the working data, respectively. (4) The working data collected by the sensor is converted from digital to digital and input into the microcontroller. Based on the collected data and the judgment of the programmed system, the microcontroller issues the corresponding output processing instructions. Four working conditions and corresponding working parameters are set: ① Normal safe stop torque Mmax, maximum working torque M1, minimum normal no-load start torque Mmin; ② Normal safe stop vibration Kmax, maximum working vibration K1, minimum normal no-load start vibration Kmin; ③ Normal safe stop speed nmax, maximum working speed n1, minimum normal no-load start speed nmin; ④ Normal safe stop current Imax, maximum working current I1, minimum normal no-load start current Imin. 1. Normal working state When the sensor detects that the centrifuge speed, torque, vibration and working current are all less than the maximum working value and greater than the minimum set value of normal start no-load, it indicates that the centrifuge is in normal working state. At this point, based on the value fed back to the microcontroller from the viscosity sensor, the microcontroller performs corresponding processing according to the pre-programmed code, namely, outputting the frequency of the inverter, changing the centrifuge drum speed, and adjusting the throughput of the feed pump. 2. Closed-loop control state: When the sensor detects that a certain value of the centrifuge speed, torque, vibration, or operating current is greater than the maximum operating value but less than the minimum set value for maximum shutdown, it indicates that the centrifuge load has increased. At this time, the microcontroller is fed back with a signal and reacts promptly according to the pre-programmed code, reducing the feed rate. Simultaneously, based on the viscosity measurement value, the control system provides a reasonable centrifuge speed to achieve the separation of weighting materials and the removal of harmful solid phases. 3. Shutdown alarm state: As long as any parameter detected by the sensor reaches or exceeds the given maximum shutdown parameter value, the control system issues a shutdown alarm command. Conclusion: This paper proposes a fully automatic closed-loop control separation scheme based on the essence of weighting material separation. It can comprehensively provide the centrifuge speed and feed pump flow rate values ​​during the separation of weighting materials, based on changes in drilling fluid performance parameters and centrifuge mechanical performance parameters. The implementation of this control system enables real-time and effective separation of weighting materials, saving on material costs, reducing mineral resource depletion, and lowering labor intensity for workers. Simultaneously, it more effectively addresses environmental pollution issues, yielding significant economic and social benefits.