I have developed a new class of sensors called pulsating sensors. The main criteria in such type of sensors is they work purely in digital domain. The sensor output is a train of rectangular pulses from which pulse frequency can be determined. The pulse frequency is a function of sensed parameter. In such type of sensors use of ADC, pre-amplifier and post amplifiers are not used. The pulse frequency is directly measured by PC, any stand alone system or even by using a frequency meter. Such type of sensors are purely digital sensors. Some experts give their opinion that it is quasi digital sensors. Hence I ask the experts to give their opinion.
IMHO, pure digital sensor must convert from input physical value to digital value without additional conversions wich have measurements with getting any additional uncertainties. Frequency measuring is compare input value with reference oscillator value. Reference oscillator frequency have the temperature drift etc. If sensor have instead PWM-output and reference frequency of measurement circuit is very high then influence of frequency drift (etc) may be negligible because we have ratio of measured (for short watch) values. IMHO, PWM-output is pseudo-digital. But frequency-output may by pseudo-digital only if reference frequency in sensor is very stable and precise and reference frequency of instruments is bigger sensor frequency, very stable and precise.
For measurement of conductance I am using a logic gate oscillator in which the resistivity part constitutes the conductance cell itself and a fixed capacitor is being used as capacitive part. When the RC oscillator circuit is powered by 5V DC, it oscillates between two logic states of almost equal duty cycles. The output is a number of rectangular pulses. The pulse frequency varies with the change in resistance of the timing circuit. Since the primary signal generated from sensor head is purely in digital domain can I not classify such sensor as digital sensor? Or will it come under quasi digital?
IMHO, primary sensor of Your device is conductance probe. Secondary parts is part of transducer wich convert primary value to frequency with 5 V digital level eg 5 V CMOS. Output signal is not code or number - measurement is needed. Me think it is quasi or pseudo digital.
You might look "The measurement, instrumentation, and sensors handbook" by John G. Webster ISBN 978-0-415-87617-9, 978-84-938347-1-5 for properly classification.
Thank you for your nice explanation with suitable reference. But what I feel since in my case the sensor output is mere digital pulse frequency which is related to sensed parameter and such approach does not require any ADC, preamplifier, post amplifier and reduces instrument hardware such sensor works purely in digital domain. This approach of instrumentation is being followed by us to develop a variety of sensors, instruments and physico chemical techniques for nuclear applications.
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