Abstract: A technique and a circuit is described for readily detecting contact resistance build-up and contact chatter. Closed contacts are arranged in series with each other and with a resistor. A voltage is applied across the series arrangement. Each contact is shorted by jumper lead and/or separately jolted. If the contact is defective, the voltage step or series of voltage pulses will appear at the junction between the resistor and the contacts in series. The voltage step or pulses are coupled through a capacitor to a normally on switch which changes state to indicate the presence of the pulse indicating the defective contact. A resistor coupled to the capacitor provides a differentiating circuit to bleed off any charge in the capacitor to permit sequentially testing each contact. A further resistor in combination with the capacitor provides an integrating circuit to assure appropriate capacitor charging in response to the negative going pulses that occur when there is contact chatter.

Abstract: A control circuit for an intrusion or other event responsive alarm device, generates an operating signal for the alarm device in response to a signal provided by a sensor. A plurality of such control circuits are ganged together, each receiving sensor signals from different sensors. The alarm device is a single unit which is responsive to the operating signal from each control circuit. The alarm device, once activated into its alarm mode by an operating signal, provides an alarm output signal to the control circuits. The control circuit which is providing the operating signal becomes latched off in response to the alarm output signal and does not respond to further sensor signals. The alarm system continues to respond to operating signals initiated by sensors associated with the rest of the control circuits. When the cause of the alarm has been resolved, the latched off control circuit is reset.