PH Sensors These are used to measure the acidity or alkalinity of liquids against the PH scale which ranges from 0 (acid) to 14 (Strong alkaline or basic). The scale is not linear so a PH change from one level to
another is 10 times stronger or weaker than the previous. The PH scale is actually the concentration of Hydrogen free ions when compared to distilled (pure) water. So PH0 = 10,000,000 times whereas PH7 = 1 and PH14 = 1/10,000,000. All of us are fairly familiar with measuring PH using litmus paper from our High School and University Days. This system uses the change of colour on chemically treated paper to give an indication of the PH level against a colour chart. However, this is not very practical for automatic monitoring hence electronic instruments have been developed that can measure PH giving an analogue or digital output, which can be compared against set limits to trigger alarms and to activate drain closure systems such as the DrainstopperTM or FlapstopperTM in the event of spills, etc. The environment is very sensitive to PH changes. A stream will normally have a natural PH of somewhere between 6 and 8. Normal rain will lie between PH 5 and 6.5. However, fish reproduction is stopped below PH5 and fish will rapidly die below PH4. So spilling vinegar PH3, lemon juice PH2 or battery acid at PH1 can be catastrophic!