thank you very kindly Lefty, i appreciate the help. the probe im using is a fork/prong type, it gives hi or lo signal to the plc depending on wether there is water in the sump tank.
i find your response very helpful in that i have always wondered how the fork type works seeing that the two forks are joined together i.e (a capacitor needs two plates and a di-electric to store charge). thanx to you i have just learned that the forks and earth function as the plates and the water as di-electric....