Abstract: A slope change detector circuit uses a differential amplifier to produce an output signal having two levels, the change of one to the other of which is indicative of a slope change in an input electrical signal. A first input of the differential amplifier communicates directly with a signal source, while a second input communicates with a signal source through a delay network. The delay network includes a switching circuit between the signal source and the differential amplifier comprising a field-effect-transistor and a capacitor; and a feed back circuit comprising a circuit that derives the absolute value of the differential amplifier's output signal and a level detecting zener diode that causes the field effect transistor to change resistance when the absolute value signal reaches a predetermined level.

Abstract: A blending-type motor fuel dispensing apparatus operates to blend together, in various proportions, two liquid motor fuels (gasolines) of different octane ratings, to produce various grades of product. The quantity and cost displays, and also the automatic control of the blend during dispensing, are based upon the summation of two sets of pulses, the number of pulses in each set being proportional to the integrated flow rate of a corresponding one of the two fuels. The pulses are counted and multiplied by a price per gallon, which has been previously set for the grade being dispensed, to provide a cost display. A pulse comparison circuit, which compares pulses representative of the flow of one fuel with a percentage (settable for each blend) of the summed pulses, is used to control the proportioning of the two fuels.