Hi guys, thanks for your support. Just joined the world of Electrical & Industrial I&C. Was going through some old legacy drawings for work and found something interesting. HLP and LLP are relays. PIA-1 is a pressure sensor which is tied to an annunciator panel. I am having trouble understanding the circuit, from what I can tell both Hi and Lo points are high impedance at normal pressure levels (in which case the Relay coils are always engaged). As soon as a fault condition is detected, one of the Hi, Lo points will go to zero impedance thereby deactivating their corresponding relay. I am guessing the resistor is current limiting. Is my understanding correct, and if so what is the purpose of the capacitor in that circuit (I believe its a 1uF Cap)?