Conductivity meters, dissolved solids meters and resistivity meters are analytical instruments that measure the conductivity, dissolved solids, and/or resistivity of a liquid sample. They can measure a single variable, a combination of variables, or all three variables. Often, because these variables are related, combination conductivity meters, dissolved solids meters and resistivity meters used. Conductivity, a measure of water’s ability to transmit electrical current, is a gross, indirect measurement of the concentration of ions. Consequently, conductivity can be used to estimate levels of total dissolved solids (TDS), a measurement of the dry mass of dissolved solids in water. As a rule, most of the colloidal particles are included in a TDS measurement. Resistivity, another related variable, is the reciprocal of conductivity.

Important Specifications

Specifications for conductivity meters, dissolved solids meters and resistivity meters include conductivity range, dissolved solids range, and resistivity range; conductivity accuracy, dissolved solids accuracy, and resistivity accuracy; and process media temperature. Portable, hand held, modular, lab, benchtop, field-use, and panel-mounted instruments are commonly available. These instruments have an analog meter, a digital display, or a video display such as cathode ray tube (CRT), liquid-crystal display (LCD), or flat panel display (FPD). Often, conductivity meters, dissolved meters and resistivity meters with manual controls have knobs or potentiometers. Analytical instruments with a digital front panel are programmed with a keypad. Programmable conductivity meters, dissolved solids meters and resistivity meters are also available.

Outputs and Accessories

Conductivity meters, dissolved solids meters and resistivity meters provide electrical outputs such as analog voltages, analog currents, and analog frequencies. Devices with a switch or alarm-relay output are also available. In terms of features, some conductivity meters, dissolved solids meters and resistivity meters are battery-powered, temperature compensated, event triggered, or designed for extreme environments. Others have filters, built-in or self-calibration, or self-test capabilities. Conductivity meters, dissolved solids meters, and resistivity meters with that provide special signal processing and/or filtering are also available. Often, these analytical instruments use Butterworth or Bessel filters. Butterworth filters provide a very flat response. There is almost no attenuation in the passband, and the roll-off rate is somewhat slower than other filters. Bessel filters have a relatively flat passband and slow roll-off. The stopband is fairly monotonic (ripple-free).

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ABB Measurement Products