The Fast Conductivity Sensor is designed to make very rapid, high resolution measurements of electrical conductivity of water. The sensor consists of four electrodes (platinum spheres) supported by fused glass. Each electrode is electroplated with an amorphous platinum coating. The picture to the right shows typical dimensions. This sensor can be used for investigating turbulent mixing in stratified fluids.

This sensor must be used in conjunction with suitable electronics such as the MicroScale Conductivity and Temperature Instrument, and SCAMP (available through PME). The sensor functions by being a dimensionally stable contact between the water around the sensor and the electronic circuit. This circuit makes a four terminal measurement of the conductance of the water supplying an A.C. current between the inner electrodes of the sensor and measuring the A.C. voltage that develops across the outer electrodes.

The conductivity-averaging nature of this sensor causes it to have the property of spatial resolution. The sensor will respond to conductivity features that are large compared to the separation between the inner electrodes and is increasingly less sensitive to increasingly smaller features.

The spatial averaging volume of the sensor can be estimated to be a sphere of radius 1/2 mm centered between the inner electrodes. This is only an approximation however of the actual sensitivity described by a complicated weighting function applied to all points around the sensor.