How do Conductivity Meters work?
Conductivity is measured by applying an alternating voltage across two or four electrodes of a cell with known geometry and measuring the resulting current. The conductance, in siemens, multiplied by the cell constant (the ratio of electrode spacing to area, in reciprocal centimeters) gives conductivity in microsiemens or millisiemens per centimeter. Alternating current at frequencies from hundreds of hertz to several kilohertz avoids electrode polarization. Conductivity rises by about 2 percent per degree Celsius, so meters compensate to a reference temperature, usually 25 degrees Celsius, using a linear coefficient or a nonlinear function for natural or ultrapure water. Cells with constants of 0.01 to 0.1 per centimeter are used for pure water, 1 per centimeter for general work and 10 per centimeter for concentrated solutions. Inductive cells use two toroidal coils and have no exposed electrodes, which suits aggressive or fouling media. TDS is estimated by multiplying conductivity by a factor of about 0.5 to 0.7.
Which Conductivity Meters variants are available?
- Benchtop Conductivity Meter — A benchtop conductivity meter is a mains-powered laboratory instrument with automatic ranging, selectable cell constants and calibration with traceable standards.
- Portable Conductivity Meter — A portable conductivity meter is a rugged battery-powered handheld instrument with IP-rated housing, automatic ranging and temperature compensation.
- Pen-Type Conductivity and TDS Tester — A pen-type conductivity and TDS tester is a pocket-sized waterproof instrument with an integrated electrode, offering ±1 to ±2 percent accuracy.
- Online Contacting Conductivity Analyzer for Pure Water — An online contacting conductivity analyzer continuously measures low-range conductivity or resistivity in purified and ultrapure water systems using a flow-through two-electrode cell and a transmitter.
- Toroidal (Inductive) Conductivity Analyzer — A toroidal or inductive conductivity analyzer measures conductivity with two coupled coils and no exposed electrodes, so it resists fouling and corrosion.
How do I choose the right variant?
Start with the conductivity range of your samples, because the cell constant must match it: use 0.01 to 0.1 per centimeter for ultrapure water, 1 per centimeter for drinking water and most laboratory work, and 10 per centimeter for brines and concentrated solutions. Then choose the format. Benchtop meters give the best accuracy and GLP features, portable meters suit field sampling and plant rounds, pen testers suit screening, and online analyzers give continuous monitoring with relay and 4–20 mA outputs. Pharmaceutical water testing requires a meter and cell that support USP <645> with temperature compensation disabled and calibration traceable to standards. For fouling or corrosive media consider inductive sensors. Check the accuracy specification, temperature compensation options, cell material and the cost of calibration standards.
Where are Conductivity Meters used?
Conductivity Meters are specified in pharmaceutical purified water testing, drinking and wastewater monitoring, boiler and cooling water control, food and beverage salinity checks and soil and agricultural extracts.
Which standards and certifications apply?
Work with Conductivity Meters is commonly governed by USP <645>, Ph. Eur. 2.2.38, ASTM D1125, ASTM D5391, ISO 7888, OIML R 68, IEC 60746-3 and GB/T 6908. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Calibrate with traceable potassium chloride standards close to the sample range, for example 84, 1413 or 12880 microsiemens per centimeter, at a controlled temperature. For ultrapure water, measure in a flow-through cell to avoid absorption of carbon dioxide, which raises conductivity within minutes. Rinse the cell with sample before measuring and store it dry or in deionized water as recommended. Platinum black coating should be protected from contamination and re-platinized when needed. Verify the cell constant periodically. Pharmaceutical laboratories should follow USP <645> or Ph. Eur. 2.2.38 staged testing and keep calibration and verification records. Keep cables away from power lines to avoid interference and ensure samples are not contaminated by handling.
