The resistive principle uses the conductivity of the liquid to be tested. The electrical current travels through the liquid and comes into contact with the electrode detecting the reached level. The probes are available with single or multi-rod or rope electrodes (max 5). Process connections are extremely varied, threaded, flanged or sanitary type with different sizes and materials. Control units associated with the resistive probes allow the user to set the sensitivity, the delay times and also to check the connections between the probe and the control units.