System for obtaining digital outputs from multiple transducers

Abstract

A method and apparatus are disclosed for deriving digital signals from analog variations of different sensing elements in a transducer. Each sensing device controls the frequency of a variable frequency oscillator, which is energized when a reading is to be taken for that specific sensing device. The periodic signal is coupled to a first counter which counts a presettable total number of cycles so as to establish a variable time period proportioned to the value represented by the then existing state of the sensing device. Concurrently, a second counter is operated for a like time interval, but counts cycles from a fixed frequency clock source at a much higher frequency. The number of cycles counted by the second counter is proportional to the analog signal from the sensing device. This arrangement enables the analog signals from the sensing devices to be digitized in sequence with compact circuitry having low power drain. The different values derived from the sensing device can be used in complex analysis of one or more parameters that are being evaluated, without danger of interharmonics, cross talk or interference between the different units. By changing the presettings of the first counter, the resolution of the transducer can be varied, enabling operation in different ranges with adequate accuracy. Also, where a number of sensing elements are used in a transducer, resolution can be selectively varied when digitizing readings from the different elements.