| 摘要 |
Apparatus for measuring the ambient light intensity of a monitored area during consecutive time intervals whereby an indication is given whenever the difference in any one of these measurements and the immediately preceeding measurement exceeds a predetermined value. The output signal of a suitable light sensing device such as a photocell is converted to a pulse train having a frequency proportional to the ambient light level and supplied to one input of an AND gate. The other input of the AND gate is connected to receive consecutive, equal duration, timing signals generated by a one shot timer circuit controlled by a microprocessor. The output of the AND gate supplies a finite number of pulses to a pulse counter, also controlled by the microprocessor. The pulse counter supplies numerical values, corresponding to the ambient light level of the monitored area during consecutive equal time periods, to the microprocessor, which computes the absolute value of the difference between each numerical value and the preceeding value, and activates an alarm or indicator circuit whenever the difference exceeds a preselected value stored in the microprocessor. Relative to measuring changes in physical quantities as sensed by devices with proportional outputs, i.e. light, sound and pressure quantities, the novel method facet hereof economically translates the above changes into data for an observer to analyze, or from which to initiate appropriate corrective or other procedural actions.
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