Tham khảo tài liệu 'newnes sensor technology handbook 2005 yyepg lotb part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 16 2. With semi-automatic command the user initiates the action. After it is triggered the system sequences through multiple functions controlled by timers or shift registers. This could include solenoid actuation to switch from measurement to reference pressure followed by the auto-reference function then a return to the measurement mode. Figure illustrates a basic semi-automatic circuit. 3. Using automatic command the system steps through multiple functions similar to the semi-automatic command. However on returning to the measurement mode additional timing circuitry triggers and after a set measurement time the sequence is restarted. Depending upon the degree of complexity desired a small microprocessor-based system and its related software could consolidate the auto-reference circuitry timing and control logic all into one unit. Auto-referencing requires an established system reference point. Batch processing and continuous processing are the two main categories of measurement cycle. In a batch process a reference condition exists at some time usually at system power-up. For example a toilet tank has a high water level prior to flushing corresponding to some reference pressure. When the flushing cycle is complete the tank is filled to the previous level. The obvious point for auto-referencing is just prior to flushing when the water is at a known level. In a continuous process there is no easily accessed reference condition. For example the volume of fluid in a water tower is being monitored. This is a function of the depth of the water and can be sensed with a pressure sensor. Unlike the toilet without actually taking a pressure measurement there is no point in time at which the depth will be known. The sensor auto-reference enable system can be used for a simple case when a known reference exists periodically. Also a reference condition actuator such as a solenoid valve can be used. It can switch the sensor input from the measured pressure to
