DEC790 High Range Conductivity Sensor for Brine, Effluent and TDS Monitoring

Product Overview

The DEC790 high range configuration is designed for water where conductivity is high and where the operator also needs to know total dissolved solids and salinity. Its top range reaches 2~10 mS/cm, TDS is reported up to 5 g/L and salinity up to 5 ppt. Typical duties include industrial effluent, brine preparation, desalination reject, mining process water, food processing wash water and cooling tower circulating water, where a single conductivity figure is not enough to describe the stream.

The measurement element is a graphite two-electrode cell. In concentrated and dirty water, metal electrodes foul and polarise quickly, and the reading drifts between cleanings. Graphite plates resist both chemical attack and surface polarisation, so the DEC790 keeps a stable reading in oily effluent, high solids streams and mildly aggressive brine. The cell is housed in a PPS body rated IP68 with a working pressure of up to 6 bar, and both ends are machined with 1 inch NPT threads for direct pipe or tank mounting.

All values are published digitally over RS485 MODBUS-RTU. That matters in an effluent plant, because the probe is usually installed at a wet well, an outfall or a sump far from the control room. A digital signal does not lose accuracy over long cable runs, and the standard 5 metre cable can be extended to 10, 20 or 30 metres on request. The probe draws about 0.2 W from 9~24 VDC, so a single 24 VDC rail can power a chain of sensors on one bus.

Handling High Conductivity and High Solids

High conductivity water is electrically easy to measure, but physically hard on sensors. Scale, biofilm, oil films and suspended solids all accumulate on the electrode surface and add a parallel conduction path that reads as a false increase in concentration. The DEC790's graphite electrodes tolerate repeated cleaning without the surface damage that metal plates suffer, and the measuring unit is a replaceable module, so a heavily fouled or worn cell can be swapped without replacing the cable, thread or mounting.

Automatic temperature compensation is applied internally against a 25 °C reference. In effluent and brine streams the temperature swing between day and night, or between batch discharges, can easily reach 10 °C, which would otherwise appear as a 20% change in conductivity. Compensation keeps the trend comparable to laboratory results and to the discharge permit limits.

Key Advantages

• Top range 2~10 mS/cm with TDS to 5 g/L. One probe covers concentrated effluent, brine and process streams that would saturate a low range pure water sensor.
• Salinity measurement to 5 ppt included. Estuary, aquaculture and desalination applications get a salinity figure without a second instrument.
• Graphite electrodes resist fouling and chemical attack. Stable readings in oily, high solids and mildly aggressive water, with less cleaning downtime than metal electrode designs.
• 6 bar working pressure and IP68 PPS body. Direct installation in pressurised pipework or continuous immersion in sumps and tanks without a separate protection housing.
• Digital RS485 MODBUS-RTU over long cable runs. Reliable data from wet wells and outfalls to the control room, with no analog drift and no shielded pair tuning.
• Replaceable measuring unit reduces ownership cost. When the cell reaches the end of its life, only the measuring module is replaced, keeping the installation hardware and Modbus address unchanged.
• Automatic temperature compensation. Readings are normalised to 25 °C so that discharge limits and laboratory results remain comparable through seasonal temperature swings.
• Low power, bus friendly. About 0.2 W at 9~24 VDC, and multiple probes can share one RS485 bus with individual Modbus addresses.

Applications

• Industrial and municipal effluent discharge monitoring, including permit compliance logging.
• Brine preparation, regeneration and disposal streams in water softening and desalination plants.
• Seawater intake, desalination reject and estuary monitoring where salinity is reported alongside conductivity.
• Mining process water, tailings overflow and thickener circuits with high dissolved solids.
• Food processing wash water, brine tanks and CIP caustic or acid solution concentration control.
• Cooling tower circulating water and blowdown control, where TDS indicates cycles of concentration.
• Textile dyeing, leather and chemical plant wastewater with high salt content.
• Aquaculture and shrimp farming ponds, where salinity and temperature are managed together.

Installation and Maintenance

Install the probe at a low point of the pipeline where the pipe runs full, or submerge it in the active part of the sump away from the sludge blanket. Point the measuring face into the flow direction and avoid dead zones where solids settle on the electrode. Keep the cable away from pump and motor feeders. After the first weeks of operation, check the probe monthly and adjust the cleaning interval to the fouling rate actually observed.

For cleaning, shake the probe in clean water. If scale or biofilm persists, soak the measuring section in a mild detergent or weak acid for 15 minutes, rinse with distilled water and verify the reading against a handheld meter. Two point calibration with standards close to the process value is normally sufficient; multi point calibration with 84, 146, 1413 and 12880 µS/cm solutions is used when the cell is replaced. Never scrape the graphite surface with a hard tool.