| 摘要 |
A control system, of the kind in which a transducer responsive to a variable quantity is responsible for initiating control effort to adjust the said quantity, is described with particular though not exclusive application to a system for obtaining precise inflation to a desired pressure setting of pneumatic tyres. A pressure transducer which provides an output voltage proportional to its input pressure determines the output frequency of a voltage/frequency converter. The output of the voltage/frequency converter is gated into a counter for a set period determined by a timer unit so that in such period the counter assembles a count which is a measure of the sensed pressure. The timer unit is adapted to divide down the local a.c. mains supply frequency so as to derive therefrom discrete timing pulses enabling cyclic operation of the apparatus within a predetermined timing framework. A user has the facility to enter a pressure target into the apparatus and, during each cyclic operation, a comparison is effected between the pressure sensed by the transducer and the set target pressure and, depending upon the outcome of this comparison, a pressure increment or decrement is affectuated as appropriate by operation of a inflate or exhaust valve. A modified embodiment having decoding and display molecules coupled to the pressure counter constitutes an electronic pressure meter. Compensation for transducer and/or voltage/frequency converter drift is described, together with variants such as for enabling extra large tyres to be rapidly inflated, and alternative applications using for example temperature sensitive or mass sensitive transducers for temperature control or weighing/batching. |
