Sensors

The combination of a device for monitoring the electrical conductivity of an electrically conductive fluid and an electronic circuit for processing signals produced by the device, said device comprising at least first and second electrical coils for immersion in the fluid, said first coil constituting a coil to be energized with an alternating electrical current and said second coil constituting a detection coil for providing a signal representative of the electrical conductivity of the fluid, the first and second coils being wound on a common magnetic core and being arranged relative to each other so that, in use, said coils are mutually inductively coupled and are inductively coupled by the fluid;

• said electronic circuit comprising a source of electrical power for supplying electrical current to the first coil, means for generating an electrical reference signal with which the electrical current supplied to the first coil is compared, a feed back circuit, which is operative in response to variations from a predetermined relationship between the reference signal and the electrical current supplied to the first coil, for stabilizing the electrical current supplied to the first coil, and a comparator circuit for comparing the stabilized electrical current supplied to the first coil with the output signal of the second coil, the comparator circuit being operable to produce an output signal indicative of the inductive coupling between the first and second coils and hence the electrical conductivity of the fluid.