• Thick-wall TEFLON membrane ensures very high stability, low-drift and high durability in aggressive industrial applications & minimizes frequency of membrane replacement
• No special maintenance needed. Just wipe the membrane periodically as required
• Galvanic dissolved oxygen cell with true zero means only slope (span) calibration is performed dry in air. No wet solution calibration is ever needed to simple field operation
• Membrane is easy to replace and electrolyte solution is simple to recharge allowing for extremely low ongoing cost of ownership and a theoretically unlimited service lifetime
• The AST-DO-UNIVERSAL D.O. sensor is not sensitive to presence of hydrogen sulfide gas
• Temperature compensation is built-in & performed automatically to ensure reliable readings

• Inline insertion depth from 0.7 inches (standard) to 2.2 inches (extended insertion depth option)
• Ready for inline or immersion use standard, submersible with waterproofing option
• Waterproofing seal option is available for complete cable isolation for fully submersible installations & applications employing field washdowns and/or moist & humid conditions
• Integral Pt1000 temperature element used to compute the percent (%) saturation value

• * Integral Smart Digital MODBUS RTU digital sensor board for low-noise operation and long cable runs as well as portability of field calibrations and configurations for plug & play hot-swap
• Fully automated calibration including corrections for air pressure and ambient temperature
• Percent (%) Saturation computed with corrections for temperature, air pressure and salinity.
• Special Calibration Percent (%) Saturation excludes salinity correction for dry in air condition
• Waterproof & Corrosion-Resistant NEMA 6P Quick Disconnect HiQ4M Snap Connector
• Up to 1,000 meters (3,280 feet) total cable length using HiQ4F/HiQ4M snap extensions
• Smart Digital HiQDT MODBUS RTU configuration has 6 meters (20 feet) of cable standard, Max integral cable length 23 meters (75 feet) cable (longer lengths possible as special orders)
• Fully submersible up to max 15 meters (50 feet) without use of an immersion rod (standpipe)
• Min and Max temp in use plus time since last calibration analytics stored. The total time in use, sensor item number, sensor serial number including year and month of manufacture also stored integral to sensor to support remote troubleshooting with all data portable inside sensor.
• Modbus implementation guide gives details for programming PLC or data acquisition device

• 1” MNPT Front Threads for Twist Lock Inline Use (0.7” Std to 2.2” Extended Max insertion config)
• 1” MNPT Rear Threads for Immersion Use or Submersible Use with Waterproofing Option

1” MNPT KYNAR® PVDF and KETASPIRE® PEEK Twist Lock Receptacles for Quick Disconnect Bayonet Style Inline Installations

Waterproofing Options for Fully Submersible Assemblies

AST-DO-UNIVERSAL HiQDT Smart Digital
RS-485 MODBUS RTU Dissolved Oxygen (D.O.) Sensors

• Programmable Logic Controller (PLC)
• Human Machine Interface (HMI) can be either local or else available via remote access
• All PLC & HMI functionality shown above is included ASTI touchscreen controllers
• PLC & HMI can be either customer supplied or ASTI provided as desired.
  • See modbus implementation guide if sensors will be interfaced to customer PLC
• Windows Software for Setup, Configuration & Calibration of HiQDT sensors
• Search & Assign sensor node address & baudrate (HHC can also search and assign node address)
• Optional for configuration & calibration if these features are not implemented in HMI+PLC
• Windows Datalogging & Graphing software records pH, ORP, D.O. ppm & % saturation, temp and raw mV values for setup of modbus network & commissioning plus pilot & research applications
• Handheld Communicator (HHC)
• 9V battery powered operation with simple easy to use 4 button operation with bright LED
• Ready for plug & play use right out of the box with zero configuration required

The AST-DO-UNIVERSAL smart digital RS-485 MODBUS RTU dissolved oxygen sensors comes factory calibrated and ready for immediate commissioning right out of the box. The AST-DO-UNIVERSAL sensors are available in the convertible configuration suitable for use in inline, immersion and submersible installations as well as the twist lock configuration for quick disconnect bayonet style inline installation for application where frequent removal from service is needed for cleaning to avoid coiling of the cable from repeated insertion and removal from the inline 1”MNPT receptacle process fitting. In addition, a sanitary & HOT-TAP configuration is available for use with the same 316SS sensor holder and other associated process mounting hardware as used for the pH, ORP & ISE sanitary & HOT-TAP valve retractable sensor assemblies.

Oxygen diffuses through the membrane onto the cathode, where it reacts chemically and then combines with the anode. This chemical process develops an electrical current, which is converted into a millivolt output signal and finally converted into the engineered ppm or percent saturation reading through the built-in internal smart digital electronics. The AST-DO-UNIVERSAL has built in temperature compensation for mg/l (ppm) units and is designed for use at temperatures between -5 and 50 °C (+23 to +122 °F) with liquid movement down to approximately 1 cm/sec (minimum flow determined at 7 mg/l and 13 °C). The smart digital RS-485 MODBUS RTU dissolved oxygen sensors support cable lengths up to 1,000 meters (3,280 feet) by any combination of waterproof extension cables or bridge boxes. Inquire to factory for special features.

AST-DO-UNIVERSAL probes do NOT need regular service; just keep the membrane reasonably clean.

If you can calibrate to the correct value you should not open the probe, even if it has been in use for a prolonged period of time (even years). If the membrane should be damaged membrane replacement will, of course, be necessary. The procedure to renovate the probe is easy and can be performed on-the-spot by anyone, as described later in this manual. Extra membranes are shipped new sensor orders and additional membranes are available as spares as are additional 125mL quantities of the internal electrolyte filling solution.

Deposits develop on all surfaces in biologically active system and various slurry and high viscosity solutions. Deposits that builds up on the membrane of an oxygen probe will change the sensitivity of that probe. The AST-DO-UNIVERSAL probes are designed so that deposits have little influence, but for the greatest accuracy you should keep the probe clean, just as it was when you calibrated it. Deposits should be wiped off the membrane with a soft cloth or paper. The cleaning frequency will depend on the accuracy desired, how fast deposits build up and on their exact nature of the build-up itself. An anti-fouling cap option is available where access to probe is difficult or deposits build-up so heavily & quickly that very frequent cleaning is necessary.

AST-DO-UNIVERSAL SENSOR INSTALLATION & MAINTENANCE GUIDE

The AST-DO-UNIVERSAL probe is easy to install. It should be placed where there is some movement in the water (approximately 1 cm/sec is enough at 7 mg/l and 13 °C for example). Ensure that the DO probe cannot strike against the tank wall and don't mount it directly above diffusers and other equipment that will give false readings. Several forms of mounting device are available for AST-DO-UNIVERSAL sensors. Inquire to the factory or your local distributor for assistance with your application. For applications where a submersible type installation approach is used either an immersion tube is used to seal the rear MNPT threads on the sensor or a suitable waterproofing option with tubing (such as WPIT or WPB/WPH) is employed for full cable isolation in which case the sensor can be suspended by just by the cable assembly alone (without a guiderod). For typical inline installation schemes, a low-flow cell suitable for 1” NPT process lines is employed.

CALIBRATION INSTRUCTIONS OF AST-DO-UNIVERSAL-HiQDT DO SENSOR 

Calibration Tips:

Take the probe up from the water process media, wipe the membrane dry, and hang the probe in free air, away from direct sunlight.  If necessary, wrap aluminum foil around the AST-DO-UNIVERSAL sensor to avoid sunlight negatively impacting on the calibration.  Be sure to wait for complete temperature equalization before performing the calibration described above.  Calibration against various "pocket" test kits cannot be recommended. For greater accuracy, a correction for barometric air pressure can be entered in mmHg units using P05 in the setup menu. The salinity correction is recommended in salt water or brackish measured solutions to ensure that the computed % saturation is accurate.  The salinity value is user entered in PSU (ppt) units and used in the computation of the percent (%) saturation value.  The salinity value is NOT used during the calibration procedure as the sensor is not immersed in the brine solution but rather dry in air.  In this way there exists two percent (%) saturation values.  One percent (%) saturation value is solely for the purpose of calibration with the salinity value not used in the computation of the percent (%) saturation value.  This is called the percent (%) saturation value.  The second normal percent (%) saturation value DOES include the salinity value provided in the computation.  Naturally if the salinity value is zero then these two percent (%) saturation values will be identical.  At the completion of a proper calibration procedure the calibration percent (%) saturation will always read 100%.  The salinity value of the measured solution can be determined from a handheld portable conductivity meter that can display the readings in salinity PSU/PPT units.  It is also possible to convert from mS conductivity units to PSU units (contact factory for assistance if required). 

How often should calibration be performed? 

Maintenance 

Automatic Calculation of Theoretical 100% Dissolved Oxygen Saturation at any Temperature & Pressure for Accurate Calibration & Measurement

The HiQDT-DO sensor has preprogrammed the correct 100% dissolved oxygen saturation levels valid at any temperature and pressure. This is important for two main purposes: 1) to ensure accurate calibration of the sensor which is performed dry in air and 2) when the percent (%) saturation is displayed and output for purposes of monitoring and control. The graph below demonstrates the impact of both temperature and pressure on the dissolved oxygen (DO) ppm levels that constitute 100% saturation condition.

For the calibration function, either the field condition should be 100% relative humidity for best accuracy or else the sensor should be suspended dry in air but over a water source to simulate locally the 100% relative humidity condition. The water molecule in air (humidity) is then saturated with oxygen in manner that can be fully described by the ambient temperature and pressure as shown above. When placed into service, the galvanic DO sensor will measure the ppm levels at the installation depth. To convert this measured ppm value into percent (%) saturation the HiQDT-DO sensor uses the internally stored curve visualization above.

Automatic Calculation of Theoretical 100% Dissolved Oxygen Saturation at any Temperature & Pressure for Accurate Calibration & Measurement

The HiQDT-DO has preprogrammed the correct 100% dissolved oxygen saturation levels valid at not only any temperature and pressure but also corrected for salinity. This is important for applications where not only fresh water will be present but also for brackish and salt water sources in variable amounts. The graph below demonstrates the impact of salinity on the dissolved oxygen (DO) ppm levels that constitute 100% saturation condition at the nominal 760mm pressure condition. For simplicity of visualization just one set of curves is shown although the analyzer can perform this compensation any temperature, pressure or salinity.

This salinity correction is only required as a correction to the computation of the % saturation from the measured DO ppm levels for the inline measurement. Since the calibration is done dry in air, salinity correction is not required for this part of operation. Since the impact of salinity is considerable as shown in the graph above, it must be corrected carefully at any level of salinity and temperature. The salinity value in standard PSU (PPT) units can be entered into the HiQDT-DO sensor to perform this correction. The value of the salinity can be determined by a handheld meter or else monitoring continuously using a conductivity transmitter from which one can readily convert into common salinity units.

Membrane Replacement of AST-DO-UNIVERSAL Industrial Galvanic Dissolved Oxygen (DO) Sensor

IMPORTANT NOTE BEFORE CHANGING MEMBRANE!
The AST-DO-UNIVERSAL sensor should not be taken apart for service unless the membrane is damaged the response (slope) is significantly reduced by fouling or deposits on the membrane that cannot be cleaned off. This is typically only the case after some prolonged period of use or an exceedingly aggressive process condition during a shorter time.

PREPARATION FOR CHANGING MEMBRANE
Unscrew the cap, rinse with water and clean the anode ONLY with a PLASTIC scouring pad. NEVER USE A METAL SCOURING PAD ON THE ANODE!
If the cathode is tarnished it can be cleaned with a 600 grade wet-or-dry paper. DO NOT POLISH THE CATHODE!

QUICK TEST
After the anode and (if necessary the cathode) was cleaned it is possible to perform a simple test to ensure the integrity of the sensor. Dry the top part of the sensor quite thoroughly, especially the cathode and the area surrounding it. Measure the output of the sensor when connected to the mating 3TX-DO or 3TX-DO-X dissolved oxygen transmitter. It should show zero ppm on the display. If your display does not read zero (or very near zero) contact factory for assistance.

See drawing to right for all referenced components in instructions:

1. Use the tool provided to unscrew the ring the ring.
2. Remove the used membrane and O-ring.
3. Rinse the cap and ring. Dry both parts thoroughly.
4. Put a new O-ring in the bottom of the cap.
5. Put a membrane on top of the O-ring.
6. Replace ring & tighten it firmly with the supplied tool.

• It is very important that all parts must be clean & dry before performing this procedure.
• Membrane must not be wrinkled before or after it is installed. If the membrane is wrinkled at any point in time it must be replaced with a new membrane immediately.
• Fill the cap to the brim with electrolyte. Hold probe upright & slowly screw on cap until it is completely flush. Some electrolyte solution may leak out during this step.
• Wait one hour before performing a calibration after changing the membrane. For best results calibrate once again approximately 24 hours after membrane is changed as the galvanic DO cell will have reached full equilibrium by this point in time.