Dissolved Oxygen Sensors FX-300-DO

Galvanic DO sensors with single to multichannel transmitters



What It Does For You

The Foxcroft FX-300-DO galvanic dissolved oxygen sensors give you extremely stable and accurate dissolved oxygen readings without the need for frequent calibration and cleaning.

The cost is dramatically lower compared to optical sensor technology; the acquisition cost is about 1/3 and ownership costs are about 1/5 of optical systems.

The sensor is a membrane covered self-polarizing active style galvanic cell which generates an electric millivolt signal that's proportional to the oxygen pressure it senses.



Provides direct DO measurements rather than indirect, interpretive results.

A durable thick Teflon™ (PTFE) membrane provides high stability, infrequent calibration and durability in difficult applications.

Insensitive to hydrogen sulfide.

No warm up time, cable sensitivity problems or drift as experienced with transmitter powered polarographic (amperometric) sensors because the sensor generates its own millivolt potential.

Automatic integral temperature compensation is performed in the sensor.

Membranes in clean water last 3-5 years and need only wiping to clean. The membrane and electrolyte can be replaced in minutes by anyone.



Auto or Manual Calibration

Automatic calibration mode reads the mV potential and assigns the correct span (slope) millivolt per ppm response for the sensor. You can also calibrate manually.

With an absolute zero point, you only need to calibrate the span while the sensor is dry in air. No solutions are ever needed.

No look up tables are required: the transmitter calculates the ppm value that's associated with the 100% saturated dry in air condition used for calibration at the temperature measured by the sensor, along with user inputed atmospheric pressure.

In clean water, calibration typically holds for one year.



The rugged membrane makes the sensor a good choice for liquids with high levels of organic material, turbidity or abrasive slurries that can foul luminescent sensors.

  • Aquaculture
  • Municipal
  • Environmental
  • Industrial

Submersible Mounting With or Without Standpipe

Sensors can be submerged by attaching to a standpipe with the 3/4" MNPT rear threads.

They can also be submerged by the cable only if ordered with waterproofing styles (WP, WP3, WP5 or WP9) that include flexible tubing to seal and encase the cable.

  • Submersible:
    • Sensors without preamplifier are fully submersible without an immersion rod or standpipe to 25 feet with optional water proofing.
    • Sensors with preamplifier are submersible up to 50-ft  with optional water proofing.

Sensors are available with or without the optional removable tip guard shown at left.







You can order a single sensor unit or up to a 5-channel system with our standard IP65 / NEMA 4X enclosures for multi-point dissolved oxygen monitoring. Larger enclosures for additional measuring points are available optionally.

Each module features up to 3,000V galvanic isolation between input and output; and separate circuit with isolation for each mating sensor.

The transmitter can measure 0-40 ppm or 0-400% saturation with a resolution of 0.01 ppm DO and 0.01 mV throughout the range, and displays values by 3-digit LED visible in sunlight.

While 0/4-20mA output is standard, transmitters with RS485 Modbus RTU output is available optionally as well.


 Download  FX-300-DO Brochure




Twist Lock, Sanitary and Hot Tap Installation

Twist Lock Style:  for inline applications that require frequent removal for cleaning. A 1"MNPT twist lock sensor receptacle screws into a standard PVC pipe tee. A quarter turn

Sanitary Style: You can mount with standard industrial 316SS sanitary fittings such as Alpha Laval Tri-Clover sensor holders with 1-1/2", 2" or 2-1/2" diameter flanges.

Insertion depth is optimized to the flange size to ensure proper positioning.

HOT-TAP Installation Hot-tap valve retractable insertion for use with 316SS HOT-TAP hardware assembly for insertion depths of 18", 30"or 42" without shutting down your process.

A shorter 12" extension tube is available for insertion only without the hot-tap hardware.




Inline Immersion Mounting

The 3/4"-14 MNPT threads can be used for inline immersion into a process. Standard insertion depth is 1-1/2". Insertion depth can be extended up to 3-1/2" maximum by special order.

For protection against wash down or wet environments the back of the sensor and cable can be waterproofed.




Sensor Specifications


 Convertible 3/4"-3/4" MNPT configuration for any mounting style

Measurement Range: 0-600 % saturation, 0-60 ppm range (Lowest Limit 0.1ppm) *
Operating Temperature:
-5 to +50 °C (+23 to +122 °F)

Temperature Element: Standard with Pt1000 temperature sensor
DO Measuring Cell Material of Construction: DELRIN® (Polyoxymethylene, POM)
Sensor Body Material of Construction: RYTON® R-4-230BL (Poly-Phenylene-Sulfone, PPS)
Dimensions: See drawing above and specification sheet(s) for details
Cable Length Without Preamplifier: Standard 10 feet (3 meters), Max is 50 feet (15 meters)
Cable Length With Integral Preamplifier: Standard 10 feet (3 meters), Max is 330 feet (100 meters)
Measurement Principle: Galvanic cell, self polarizing (a.k.a. active type) & internally self temperature compensating.

Signal Response Wetted in Solution: Slope (span) is 1mV to 5mV per DO ppm depending on exact conditions
Signal Response Dry in Air: Typically 10mV to 40mV depending on exact conditions
Signal Response Time: Typically 10 to 20 seconds near ambient (response time is temperature dependent)
Signal Response Resolution: 1% saturation absolute
Signal Response Repeability: Typically ±1% of actual measurement under the exact same conditions
Calibration: Slope (span) determined from automatic dry in air calibration. No zero calibration required for true galvanic DO cell.
Initial Impedance Without Preamplifier: < 2 MegaOhms @ 25°C
Initial Impedance With Preamplifier: < 2 KiloOhms @ 25°C
Flow Requirements, Water: Minimum flow dependent on DO and temperature, typically 1 cm/sec, suitable for most uses
Supplied With: 10 each spare thick high stability membranes with O-rings, 125 ml electrolyte filling solution,
Tool for installation and removal of membranes from ring inside cap

* Contact factory if you plan to measure dissolved oxygen levels above 400% saturation or 40ppm prior to purchase.


Click to see how to replace the membrane




NEW! Smart Digital DO Sensors With Modbus RS485 RTU Output

Plug and play smart sensors can interface directly with any PLC, computer or data acquisition device that can be configured as a RS485 Modbus RTU master.

Smart sensors can be connected to our SSM smart sensor manager for calibration anywhere or to be used as a portable measuring device to spot check your system or troubleshooting.

Interface requires an isolated, dedicated RS485 input and an isolated 9 or 12VDC power supply or a DC/DC isolator and converter


Web page coming soon

 NOTE: If you have an immediate need we can quote systems while the web materials are being produced.