pH measurement is a important parameter in controlling the acidity of the geothermal fluid. A low pH indicates acid fluid, which might enhance the corrosion of the pipes. pH-meters are instruments calibrated at a temperature different from geothermal fluid, so the geothermal fluid must be cooled to the same calibration temperature of the pH-meter to get an accurate results.
pH measurement of the geothermal fluid in situ must be first cooled by passing the separated geothermal fluid through a cooling tubing surrounding by cold water. The cooled solution is collected in a container, where the pH-meter is introduced to measure its value.
Here is an illustration of this measurement.