Alarm detector responsive to rate of change of a monitored condition Patent #: 4065758
ApplicationNo. 05/956001 filed on 10/30/1978
US Classes:340/644, Switch or relay340/661, Comparison340/664, Current361/159Including means for using, or compensating for, the induced EMF of the electromagnetic device
ExaminersPrimary: Brigance, Gerald L.
Attorney, Agent or Firm
International ClassesG01R 31/00 (20060101)
H01F 7/18 (20060101)
H01F 7/08 (20060101)
AbstractA first amplifier measures the instantaneous voltage across a resistor, connected in series with the electromagnet of a solenoid valve, as the current increases following energization of the electromagnet. A second amplifier measures the same voltage and stores the peak value in a capacitor. The two measured voltages are applied to a comparator which detects the difference, and generates an output, when operation of the electromagnet armature causes a transient reduction in the resistor voltage. Initial energization of the electromagnet sets a memory and starts a monostable timing period. The set output of the memory primes one input of an AND gate, the second input being inhibited by the monostable output during timing. If the electromagnet armature operates normally, the comparator output resets the memory and removes the AND gate priming signal prior to completion of the timing period. If the armature fails to operate the monostable output following the timing period completes the actuation of the AND gate to produce a fault signal.