PRINCIPALE OF OPERATION
The membraned amperometric sensors are enhanced with a third, reference electrode which eliminates zero drift. (NB. These chlorine sensors are often known as polarographic sensors although this is a misuse of the word polarographic). Its unique design means that pH compensation is not usually required at all, completely eliminating reagents.
The free chlorine sensors used by the analysers are largely pH independent meaning that the measurements are bufferless and reagentless. They are amperometric sensors and show remarkable sensitivity and stability. For those needing to measure chlorine at high pH (>pH 8.5) on variable pH water it is possible to provide pH compensation from either a pH sensor connected to the transmitter or from an external pH meter.
The sensors work by separating the electrodes that perform the measurement from the sample, by a membrane. This membrane allows the free residual chlorine (HOCl and OCl–) or the total residual chlorine (HOCl and OCl– plus chloramines) through the membrane. Inside the sensor the dissolved chlorine meets the electrolyte which is at a low pH. This converts the majority of the OCl– to HOCl. The HOCl is reduced at the gold working electrode and the current generated is proportional to the chlorine present, and the instrument gives a reading in ppm or mg/l.
This technique is the most advanced method of continuous chlorine measurement and has many benefits to the user including a very stable online measurement and better dosing control.
The HaloSense range is bufferless and reagent free, meaning that it has a low total cost of ownership and with maintenance intervals at 3 or even 6 months. HaloSense is fast becoming the instrument of choice for the engineer who wants the best instrument at the best price.