4220 Flow Meter Section 5 Options and Accessories
5.8The Temperature Probe
Figure 5-2 Temperature Probe
5.9 The pH Probe
The Parameter Modules themselves plug into the Parameter Probe connector on the flow meter.
CAUTION
The pH and D.O. probes require continuous submersion after installation, or they will lose sensitivity. Prolonged dehydra- tion of the sensor bulb may damage or even ruin the pH probe.
The temperature probe is the simplest of the three, consisting of a thermistor inside a metal housing. The thermistor changes resistance with an increase or decrease in temperature. The flow meter converts this resistance change to a temperature reading and displays it, in degrees Celsius or Fahrenheit, as chosen by menu selection.
The pH probe measures the acidity or alkalinity of an aqueous solution by determining the relative quantity of dissociated hydrogen ions, H+ (actually H3O+) in the solution. A larger quantity of H+ ions indicates acidity, while a smaller quantity of H+ ions indicates alkalinity. The H in pH stands for Hydrogen and the p stands for power.
The normal scale for pH runs from 0 to 14, with 0 being most acidic and 14 being most alkaline. Distilled water at 25° C is neutral at 7, based on the fact that the dissociation constant (number of H+ and OH– [hydroxyl] ions present) for pure water at that temperature is
