Conductivity Meters, Dissolved Solids Meters and Resistivity Meters
Conductivity meters, dissolved solids meters, and resistivity meters are analytical instruments that measure either conductivity, the amount of dissolved solids, or resistivity of a liquid sample. The meters can measure either one or a combination of these qualities. Because the qualities are so similar, combination meters are common instead of a meter that measures just one of these.
Conductivity in units of mhos/cm or Siemens/cm is a measure of water’s ability to transmit an electrical current. It is a gross, indirect measurement of the concentration of ions and consequently can be used to estimate total dissolved solids (TDS) levels. TDS is a measure of the dry mass (mg/l) of all the dissolved solids in water. Most of the colloidal particles will be included in a total dissolved solids measurement. Resistivity is the reciprocal of conductivity.
Typical specifications are the measurement range, accuracy and the temperature of the process media being measured. Conductivity meters, dissolved solids meters, and resistivity meters may have some controller functionality such as set limits, regulator, P/PI/PID as well as control relay output.
Mounting options for the instruments are quite varied. Conductivity meters, dissolved solids meters, and resistivity meters may be handheld meters, larger portable meters with wheels or handles for carrying, and modular for interfacing with sensors of different input ranges. Other styles commonly available are specially designed for lab or benchtop use and others for field or in-situ applications. Some of these meters are designed to be mounted in a panel.
Displays for the instruments may be analog meters, a numeric or alphanumeric digital display or video, a CRT or LCD style. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can operated through a host computer. To simplify the instruments, devices without user controls are available, as well.
Electrical output options are the standard voltage and current outputs as well as an analog frequency or a change in state of switches or an alarm.
Features available for many conductivity meters, resistivity meters and total dissolved solids meters include temperature compensation, battery power for greater portability and built-in signal processing filters. Built-in calibration ability and self-test functions are also available, as are event triggering and ratings for extreme environments.
