Fluid conductivity sensor

The sensor includes electrodes 24,30 adapted to be exposed to the fluid, a voltage source 38, a load 50, in particular an electro explosive device in a parachute canopy release mechanism, a firing capacitor 56, a conductivity sensing circuit branch including a sensing circuit capacitor 60, and a switch 66 connected in controlled relation to the sensing circuit branch and in controlling relation to the firing capacitor 56. In response to the electrodes being exposed to seawater, current flows to charge capacitor 60 via a relay coil 70 causing relay contact arm 74 to connect firing capacitor 56 in parallel with capacitor 60. As capacitors 56, 60 become charged the relay 66 drops out connecting firing capacitor 56 across device 50 for operation thereof. A current regulator diode 100 or a resistor (126) (Figs. 4,5), functions to keep the flow of current through device 50 below its firing level if the electrodes become exposed to rain; or under salt fog conditions presenting essentially a short circuit between the electrodes; in such conditions capacitor 60 effectively blows the voltage caused by the slowly rising conductivity thus preventing operation of relay 66. A semiconductor switching means may be used instead of relay 66.