Conductivity Systems . . .

Basics

The electrolytic conductivity is a sum parameter that measures all dissolved ions in aqueous solution. The unit for conductivity is Siemens (1 Siemens = 1/Ohm).

Here are some examples (MATTHES)

0,042 µS/cm	ultrapure water (20°C)
0,5 .. 5 µS/cm	deionized water
100 .. 300 µS/cm	Soft ground water
45000 .. 55000 µS/cm	Sea water
> 100000 µS/cm	Concentrated acids or lyes

Conductivity is an easy and quick way to detect changes in the salt content. However, the information on the chemical composition of a solution is only slight. A mayor advantage is the ease with which continuous or spot measurements can be carried out. Conductivity can be measured conductively or inductively.

Kuntze Instruments Measurement

For conductive measurements the sensor consists of two electrodes in direct contact with the water. Between these electrodes, an alternating potential is applied. This causes all charged particles in the water to move, giving rise to a current as a function of the number and velocity of the ions. The water with its ions behaves like a resistance, and the conductivity is the reciprocal expression of said resistance. The current also depends on the dimensions of the electrodes, so the sensor influence is eliminated by means of the so-called c value. A temperature sensor is integrated in the conductivity sensor to compensate temperature effects. For an inductive measurement, the sensor contains two coils integrated in a cylindrical housing. Through one coil flows an alternating current, generating an electromagnetic field. This induces a current in the other coil. Water flowing through the cylindrical sensor affects the strength of the current according to its conductivity. Here again the sensor design has an influence on the signal, and this influence is eliminated by means of a c value. A temperature sensor is integrated for temperature compensation. Inductive measurement is used in applications where particles and sedimentation may affect the measurement, and in aggressive solutions that may corrode the open metal electrodes of a conductive sensor.

ASR Self Cleaning Technology for Conductivity

description

The cleaning is carried out electrochemically by electrolysis of water: H2O --> O2 + H2. 
The electrochemical cleaning acts threefold: the generated gases hydrogen and oxygen blast away even persistent coatings. Oxygen oxydizes organic compounds, and hydrogen reduces rust and manganese oxide and likewise destroys organic coatings.

The produced gas volumes are small and unused gas molecules recombine automatically to the water they stem from. The cleaning is activated in the menu of the measuring and control instrument. The starting time of cleaning can be defined by the user. The cleaning cycle lasts approx. 20 seconds. The measuring value is locked for five minutes, in the display, in the output signal, and also for the controller, to give the electrode time to polarize. The cleaning can be set to 0/1/2 times per day. ASR aims at keeping the sensor clean from the beginning. It was not meant to clean already coated sensors, since with those sensors the signals will be higher after cleaning, making a recalibration necessary.