Novel Valve for Automatic Calibration of a Chloride Sensor for River Monitoring

Chloride is the most abundant negatively charged ion in extracellular fluid. Chloride can destroy river habitats and affect cement and steel structures, so its monitoring is required. Remote-sensing water monitoring for detecting pollution points requires of auto-calibrated chloride-ion-sensitive electrodes, as their calibration is lost after 2 h. A valve was designed using two stepper motors, which, depending on their position, allowed calibration reference liquid injection, as well as distilled water and sampling water flow towards the sensor cavity. The stepper motor routines for sensor cleaning, sensor calibration and water monitoring are explained in this paper. Sensor cavity levelling to 0° was essential for proper operation, and the valve can work properly with any sensor using two-point calibration. The automatic device measured continuously for 7 days when the valve was fixed outside the water. Continuous measurements were taken in an effluent of the River Texcoco near Mexico City.