Wholesale Salinity Sensor 4-20mA Manufacturers & Factories

Salinity represents the mass of dissolved inorganic salts per unit mass of aqueous solution, typically expressed in parts-per-thousand (ppt, g/kg) or Practical Salinity Units (PSU). Pure sodium chloride solutions at 25°C exhibit predictable relationships (for example, standard standard seawater at 35 PSU equates to approximately 53.0 mS/cm at 25°C). BOQU 4-20mA salinity sensors utilize built-in microprocessors executing standard PSS-78 oceanographic polynomial conversions as well as linear TDS factor mappings, transmitting direct, calibrated salinity over the scaled 4-20mA current loop.

Contacting 4-electrode sensors use metal pins (graphite, stainless steel, or platinum) that come into direct physical contact with the process fluid. While modern 4-electrode circuits compensate for minor polarization, they remain vulnerable to mineral scaling, microbial slime coatings, and abrasive particulates. Toroidal sensors encase magnetic drive and pickup coils completely inside seamless, chemically inert PEEK or PVDF plastic. The liquid forms a closed electrical loop through the sensor donut aperture. Without exposed electrodes, toroidal sensors are immune to metal fouling, coating errors, and chemical attack, making them the superior choice for high-salinity brines and wastewater applications.

In large industrial facilities, metal pipelines, pumps, tanks, and structural steel often maintain subtle differences in electrical potential (voltage). When an un-isolated sensor immerses into conductive salt water connected to a grounded PLC, stray DC and AC ground currents flow through the sensor circuit, causing offsets (e.g., reading 12mA instead of 8mA) or destructive electrolytic pitting. BOQU 4-20mA salinity sensors incorporate internal optical and magnetic DC-DC isolators (>1,500V DC breakdown rating) that decouple the wet electrochemical measuring circuit from the external 24V DC power loop.

Because 4-20mA loops convey data as current rather than voltage, line resistance does not attenuate the signal so long as the power supply voltage exceeds the combined loop load (total cable wire resistance + receiver burden resistor). Using standard 18 AWG shielded twisted pair cable (approx. 21Ω/km loop resistance) and a 24V DC supply driving a standard 250Ω PLC input card, transmission distances up to 1,000 meters (3,280 feet) can be achieved with zero signal degradation.

Shanghai BOQU Instrument supports agile procurement for engineering contractors and regional equipment distributors. Standard sample testing orders have an MOQ of 1 unit. Batch wholesale orders start at 10 units. Typical production lead time for standard models is 3–7 business days; custom OEM batches (custom cable length, customer-branded label, specified 4-20mA scaling, and private protocol mapping) ship within 10–14 business days backed by complete factory test certificates.