When there is NO mains power supply… Monitoring Water Quality sets new challenges!! - David Precious

Measuring Water Quality in Remote Locations
When you need to measure water quality in the middle of nowhere special techniques are needed to minimise energy use and recover data remotely. Combined sewer overflows, unmanned sewage treatment plants and water treatment work’s intakes are all locations that may need to be monitored. Minimising the power consumption through careful power budgeting of the overall system is the first crucial step, but alternative battery charging methods and a complete understanding of the measurements to be made are also essential. More complex analysis techniques for parameters such as ammonia, nitrate and phosphate may be possible through integrated design.

Design for Low Power
The principle of conserving power use is at the core of good low power remote system design. Systems have three modes. For most of the time the equipment is in the lowest power ‘standby’ mode. In this state the only function in operation is the real time clock that is set to ‘wake up’ the instrument at the appointed interval. During the measuring phase the sensors and main microprocessor are powered up and the measuring cycle for the particular sensor takes place. The time taken to make a set of measurements will depend on the parameters being monitored. Simple measurements such as dissolved oxygen or pH can be completed in a period of say 30 seconds whereas a specially designed ammonia monitor may take 15 minutes or more to make a measurement. The frequency at which measurements are taken is a key factor and readings at hourly or two hourly intervals will give good background information whilst reducing power drain. Closer intervals may be needed to catch short-term events and in some cases the rate of measuring can be increased automatically when an out of limit condition is detected. When calibration is required the system is powered up into service mode allowing full use of the calibration functions.