A multiple-channel conductometer for measuring salinity concentrations in laboratory flows is described. Channel-to-channel influence and sensitivity to extraneous grounds have been reduced to acceptable levels by a unique probe excitation and detection system which keeps the fluid at ground potential. Conductivity rather than resistivity is measured to eliminate nonlinear concentration-voltage relationships, and special circuits are included to make calibration curves independent of the cable length between probe and instrument. The system has been designed with outputs suitable for analog and/or digital processing and with emphasis on ease of operation and reliability. The electronic system utilizes operational-amplifier technology jointly with discrete components to optimize signal processing and to take advantage of recent advances in the electronic industry.