Selecting Conductivity Sensors Part 1: Operating range and Temperature/Pressure Specifications
Conductivity is one of the most widely used parameters in the analytical measurement world. It can determine drinking water quality in a municipal water system, it may determine if the rinse water in a plating process will leave spots on a metal surface and in some industries it is used to monitor the concentration of various chemicals.
Conductivity sensors have specific cell constants that dictate their minimum and maximum measurement capability as illustrated in the chart below. Smaller cell constants are designed to measure cleaner water, while larger cell constants are best suited for dirty water, or processes that contain chemicals and other contaminants. The key to assembling a successful Conductivity system begins with the selection of the sensor.
Determine the general operating range
• Most applications will experience fluctuations in conductivity levels during normal operation, caused by the process itself (cleaning/rinsing), fouled filters, addition of chemicals, or a change in the influent water source. These variations must be within the measurement range of the sensor.
• Choose a sensor whose actual operating range fully encompasses the conductivity range of the application. (Example: if an application has a conductivity range of 900 to 1000 µS, select the 3-2841 instead of the 3-2840.) See the chart below.
Safety Considerations Knowledge of the temperature and pressure of the process is critical to ensure the safety of staff, facility, and equipment. Signet publishes temperature and pressure specifications in the technical reference section of the Signet catalog. Review these specifications thoroughly before making a final selection. Remember to check the specifications of the process connection (tee, saddle) where the Signet sensor will be installed. Threaded tees and saddles may have much lower temperature and pressure capabilities than the sensor itself.
Notes:
• Signet sensors are delivered with process fittings made of polypropylene (PP), PEEK or stainless steel.
• Thread choices include ¾ in. NPT or ISO 7/1-R¾
• Sanitary tri-clamp flanged connections are available for lower cell constants only.
• Signet can upgrade the process connector and sensor materials to meet specific temperature and pressure requirements. (Special order, contact GF for details).
Coming Next: Part 2: Chemical compatibility Part 3: Proper Sensor installation
