The control system of the HPHT Hydraulic Cubic Press significantly influences diamond grade (e.g., crystal integrity, impurity content) by precisely regulating key parameters such as temperature, pressure, and time during synthesis. Below is a detailed analysis of the mechanisms and technical implementations:

‌1. Closed-Loop Control of Temperature and Current‌
‌Traditional Issues‌: Early systems used constant voltage control, which led to unstable heating due to power fluctuations and contact resistance variations, resulting in inconsistent diamond growth conditions.
‌Improvement‌: Closed-loop PID current control technology was adopted, where analog output precisely adjusts thyristor conduction angles to ensure current strictly follows preset curves.
‌Effect‌: Direct current control stabilizes cavity temperature, improving crystal uniformity and purity.
‌2. Dynamic Pressure Compensation Technology‌
‌Control Method‌: A lower pressure threshold (e.g., activating a small pump when pressure drops 0.15 MPa below the set value) and an upper limit (e.g., stopping at 0.05 MPa above) maintain dynamic equilibrium.
‌Advantage‌: Reduces seal friction interference, limiting pressure fluctuations to ±0.05 MPa, providing a stable high-pressure environment for diamond growth.
‌Impact‌: Stable pressure minimizes crystal defects, increasing the proportion of high-grade diamonds (e.g., 40/50 mesh Ti and TTi indicators).
‌3. Multi-Parameter Protection System Reduces Abnormal Losses‌
‌Absolute Protection‌: Immediate shutdown upon exceeding limits for pressure, current, or voltage prevents equipment failure-induced damage.
‌Relative Protection‌: Monitors abrupt pressure changes or resistance deviations, preemptively alerting to material or system anomalies.
‌Data Comparison‌: With improved protection, anvil consumption dropped from 2 kg/10k carats to 0.5 kg/10k carats, and failure-related losses decreased from 18% to 6.9%.
‌4. Optimization of Process Parameter Matching‌
‌T-P-t Coordination‌: Industrial computers automate the synchronization of temperature (T), pressure (P), and time (t) curves to meet high-grade diamond growth requirements.
‌Result‌: The yield of premium diamonds rose from 20% (manual control) to 65% (automated control), with 40/50 mesh Ti indicators improving from 3.2 to 86.
‌5. Future Development Directions‌
‌Electro-Hydraulic Proportional Control‌: Enhances precision in six-cylinder displacement and ultra-high-pressure regulation.
‌Frequency Conversion Technology‌: Replaces small pumps to reduce pressure surges, enabling fuzzy PID control.
‌PLC and Configuration Software‌: Improves anti-interference capabilities and supports centralized control with data analysis.
Upgrades in the HPHT Hydraulic Cubic Press control system (e.g., PID closed-loop control, dynamic pressure compensation, multi-parameter protection) have markedly enhanced diamond grade consistency and yield while reducing production costs.