| 摘要 |
A grinding process, e.g. for cement, is automatically controlled in dependence on a combination of measured variables of the process and the control is overridden by further automatic control if one of the variables varies beyond a predetermined limit. As described, motor-driven feeders respectively supply clinker and gypsum to a two-compartment grinding mill and oversize particles in the output are separated and returned to the input. A microphone is associated with each compartment to derive signals, which are suitably filtered, representative of load, and wattmeters are respectively associated with motors driving the separator and an elevator for mill output to derive further signals representative of load. Adjustable portions of these four signals are added and any deviation of their sum from an adjustable reference is effective through a transistor amplifier to control the speeds of the motors driving the clinker and gypsum feeders so that mill load is maintained between predetermined limits. The transistor amplifier is associated with biassed diode limiters and has differential feedback to introduce an integral component of control. If the control signal remains below a predetermined value for a predetermined period an alarm is operated to indicate a deficiency in the feed to the mill. Each of the four signals is also prevented from exceeding a predetermined limit by application to separate transistor circuits which can override the main control system by reducing its reference value. Different combinations of load detectors and the use of temperature variable resistors as load detectors are referred to. |
