The ABB Model 9408 Dissolved Oxygen System is an instruction manual for dissolved oxygen measuring systems, primarily designed for use in sewage treatment works where fouling of the dissolved oxygen sensor by rags or other large solids is a common occurrence. The manual details the installation, operation, maintenance, and specifications of the 9408 Series, which includes Floating Ball, Dip, and Submersible system types.
Function Description
The core function of the 9408 Series is to measure dissolved oxygen in various industrial process control, flow measurement, gas and liquid analysis, and environmental applications. The Floating Ball system, in particular, addresses the issue of sensor fouling by mounting a flat-ended sensor inside a large-diameter flotation collar, making it difficult for contaminants to collect. The Dip and Submersible systems are designed for use in open tanks and difficult-to-access areas. All measuring systems are compatible with the 4640 and 4645 dissolved oxygen transmitters. A water wash option is available across all dissolved oxygen systems described, helping to maintain sensor cleanliness.
Important Technical Specifications
Sensor Type:
Response:
- Typically 20 seconds for 90% of a step change of oxygen concentration at 20°C.
Temperature Compensation:
- Automatic correction by means of an integral Pt 100 resistance thermometer.
Accuracy:
- ±0.2 mg l⁻¹ or ±2% saturation within ±10°C of the calibration temperature in the range 0 to 35°C.
Operating Temperature Range:
Operating Pressure:
Dimensions:
- Floating Ball:
- Ball diameter: 203 mm
- Boom, outside diameter: Metric 50 mm, Imperial - 1⅞ in (48 mm approximately)
- Boom length: Assembled 3 metres, Kit 3 metres (user supplied)
- Dip Tubes:
- Assembled (metric): 1, 2 or 3 metre options, 40 mm outside diameter
- Kit (Imperial): User supplied, 1.9 in outside diameter
- Submersible:
- Diameter: 40 mm
- Length: Approximately 265 mm (335 mm with water wash)
- Cable length: 10 m
Materials of Construction:
- Boom: ABS
- Sensor body: ABS
- Flotation ball: Polypropylene
- Tube on dip system: Polypropylene
- Body of submersible system: Polypropylene
- Bracket metalwork: Stainless steel
Extra Connection Cable:
- Part No.: 0233-828
- Maximum distance: 100 metres (328 feet)
Water Wash System (Solenoid Valve - user supplied):
- Brass body: 2/2, NC
- Orifice size: 3.0 / 4.0 mm
- Port size: ¼ in – ½ in BSP or NPT
- Pressure: 0 to 6 bar
- Coil: 24 V a.c., 110/115 V a.c. or 230/240 V a.c. 50/60 Hz
- Maximum water pressure at electrode: 50 psi (4 bar).
Usage Features
System Types:
- Floating Ball System: Available in assembled (9408 700, 9408 702) and kit versions (Metric 9408 750/752, Imperial 9408 760/762). The assembled version comes with a 3-meter boom, while kit versions require the user to supply the boom. Designed to prevent fouling in sewage treatment works.
- Dip Systems: Available in assembled (1m, 2m, 3m options: 9408 710/712, 9408 720/722, 9408 730/732) and kit versions (Standard 9408 771, Water Wash 9408 773). Suitable for open tanks and difficult access.
- Submersible Systems: Available in standard (9408 600) and water wash (9408 602) options. Designed for suspension on a small chain to prevent cable strain and allow lowering to the required depth.
Installation:
- Detailed instructions for assembling kit systems, including cementing components and threading cables.
- Specific installation procedures for Floating Ball, Dip, and Submersible systems, including mounting to handrails or supporting structures.
- Water wash systems require a user-supplied solenoid valve and adherence to local water authority bylaws. Maximum water pressure at the electrode should not exceed 50 psi (4 bar).
Electrical Installation:
- Clear guidance on connecting the system's cable to 4640 and 4645 dissolved oxygen transmitters, with terminal sleeve colors specified.
- Advises sufficient spare cable for manipulation during installation and servicing.
Calibration:
- Sensor calibration procedures are detailed in the 4600 Series Transmitter Unit Operating Instructions.
- Recommends switching off the water wash before calibration.
- Includes steps for removing the system from its bracket, cleaning the sensor capsule, fitting a protective shroud (for floating ball types), and then calibrating.
Maintenance Features
Oxygen Sensor Capsule Replacement (8012-170):
- Storage: Emphasizes storing sensors in a dry, cool environment, using them in date rotation, and not allowing them to dry out, freeze, or be exposed to high temperatures/direct sun.
- Procedure: Detailed steps for replacing the sensor capsule, including unscrewing securing rings, removing the ball (for floating ball), cleaning the sensor block, and carefully handling the new capsule to avoid damaging the membrane.
- Life Expectancy: Typical sensor life is approximately 12 months.
Oxygen Sensor Block Replacement:
- Comprehensive procedure for replacing the entire sensor block, including disconnecting cables, slackening cable glands, removing end caps, and re-assembling with the new block.
- For floating ball systems, this involves withdrawing the ball from the elbow union and unscrewing the sensor block from the sensor pipe.
- For dip systems, it involves removing the protective shroud instead of the ball.
Temperature Compensator:
- For Floating Ball and Dip Systems, the temperature compensator is an integral part of the sensor body and is not maintainable separately; the complete sensor body must be changed.
- For Submersible Systems, the compensator is housed within a sealed unit and is not accessible for maintenance, except for sensor capsule replacement.
General Maintenance:
- Regular maintenance is limited to periodic cleaning and calibration.
- Information on a conversion kit to change the standard bracket into a swivel bracket for easier access to the floating ball sensor.
The manual also includes a spare parts list for Floating Ball, Dip, and Submersible systems, detailing part numbers for components like ball float assemblies, bracket assemblies, oxygen capsules, sensor bodies, shrouds, and gaskets.
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