ATI Model Q45D-ODO Optical Dissolved Oxygen monitor utilizes a fluorescence-based sensor to provide a reliable oxygen measurement. This sensor will provide years of service and, unlike other optical sensors, will not be degraded by exposure to direct sunlight.

The optical dissolved oxygen sensor contains a fluorophore element that absorbs liqht at one wavelength, and then radiates light at a different wavelength (fluorescence). Oxygen molecules collide with the fluorophor which causes a non-radiative reaction, meaning the fluorophore element gives off less light. In short, molecular oxygen reduces (quenches) fluorescence and the concentration of dissolved oxygen can be determined by this quenching process.

All dissolved oxygen sensors are affected by process coating. Any material that slows the diffusion of oxygen into the reaction cell will cause an error in the oxygen reading. If the system doesn’t have a means to clean itself, the sensor will require frequent manual cleanings, which means higher maintenance costs. Our self contained Auto-Clean system generates a series of high pressure air blasts to remove foulants from the face of the sensor. Each cleaning cycle lasts approximately 3 minutes, during which the monitor outputs are placed in a HOLD condition to prevent false readings or alarms. The user can vary the cleaning cycle frequency from as often as once every two hours, to as little as once a day. ATI was the first to introduce a dissolved oxygen system that cleans itself with air. Others have tried to copy our system, but none are more effective at removing biological growth and other contaminants than the ATI Auto-Clean system. So don’t be fooled by imitation air pump cleaners that are minimally effective at cleaning your sensor. Trust the original Air-Blast system. Trust the best.

Dissolved Oxygen Monitor(s) shall be supplied for continuously monitoring D.O. concentrations in (Specify Application and one or more Locations). Dissolved oxygen systems shall consist of a D.O. sensor, an electronic monitor housed in a NEMA 4X enclosure suitable for wall, pipe, or panel mounting, and accessory mounting hardware as described below.

Dissolved oxygen sensors shall be of the optical type. Sensors shall use a fluorescent material that is susceptible to non-radiative quenching by interaction with dissolved oxygen. A light source of a given wavelenght inside the sensor shall illuminate the fluorescent material, which absorbs the energy from the light source and reaches an excited state. The material then emits light at a differenent wavelength, which is sensed by a photodetector inside the sensor. Dissolved oxygen that diffuses into the fluorescent material “quenches” the reaction. The degree of quenching that occurs is directly proportional to dissolved oxygen concentration. The sensor assembly shall also contain a precision RTD temperature sensor to continuously measure sample temperature to allow temperature compensation of the measured oxygen value.

The D.O. sensor shall be supplied with an integral system for automatically cleaning the sensor while still immersed in the aeration tank. The frequency of cleaning shall be programmable in the electronic monitor from once every hour up to once every 24 hours. The system shall perform automatic sensor cleaning using a high pressure air jet to scour the sensor face of accumulated deposits, with the analog and digital outputs unaffected by the cleaning process. The air cleaning nozzle assembly shall not protrude outside the overall sensor diameter so that fibrous material will not snag on the cleaning assembly, and all air tubing shall run inside the mounting pipe to further avoid fouling problems. Sensors with tubing and cable running up the outside of the mounting pipe are not acceptable as “equal” to the specified equipment. The cleaning procedure shall not require an operator to activate, but shall be designed so that an operator can manually start the cleaning sequence if desired.

The Dissolved Oxygen Monitor electronic assembly shall be: (select one version below)

A. A loop-powered 2-wire instrument providing an isolated 4-20 mA output proportional to dissolved oxygen into a maximum load of 500 ohms.

B. An AC powered instrument for operation on (specify either 115 VAC or 230 VAC) single-phase line power. The monitor shall provide two isolated 4-20 mA outputs configurable for dissolved oxygen, temperature, or PID control. Analog outputs shall be both ground isolated and isolated from each other. AC powered dissolved oxygen monitors shall also contain two SPDT relays.

C. A battery operated data logging monitor capable of operating from an internal 9 VDC battery. The monitor shall provide two 0-2.5 VDC outputs suitable for use by the internal data logger. The monitor shall operate for up to 4 days continuously on an alkaline battery and up to 10 days on a lithium battery.

The dissolved oxygen monitor electronic assembly shall provide a variety of functions as follows.

1. Provide user selectable display of PPM dissolved oxygen, process temperature, or PID % output on the main display. Main display variable shall be indicated with a minimum character height of 0.75” to allow easy readability up to 20 feet away.

2. Allow selection of operating ranges of 0-20 PPM, or 0-40 PPM. Display ranges shall be configurable by operators, or the monitor may be configured for Auto-Ranging. The auto-ranging function shall automatically switch to the display range that provides the best resolution for any given operating level.

3. Provide the ability to use the 4-20 mA output for PID control. Proportional, Integral, and Derivative functions shall be user adjustable, and also provide for output hold when needed.

4. When operated on AC power, provide two isolated 4-20 mA outputs, with output spans programmable by the user for any segment of a display range.

5. Provide output hold and output simulate functions to allow for testing or remote receiving devices or to allow maintenance without disturbing control systems.

6. When operated on AC power, provide two SPDT relays. Relays shall be programmable for either control or alarm function, or relays may be assigned to diagnostic functions for use in indicating trouble conditions at a remote location.

7. Diagnostic functions shall be incorporated into the transmitter. The 4-20 mA output shall be capable of being assigned to safely rise to 20 mA, fall to 4 mA, or be left alone, during diagnostic failures. Diagnostic error messages shall be displayed in clear language; no confusing error codes shall be displayed.

8. When operated from a 9 VDC battery, provide data logging of dissolved oxygen and temperature over programmable time intervals. Provide software with the data logger for easy data download to standard computers, with graphical and tabular viewing of data. Software shall allow export of data to standard spreadsheet programs.

The complete dissolved oxygen monitor shall be supplied with spare parts and accessories for up to 2 years of operation. A minimum of 10 replacement membranes shall be supplied for the sensor.

For each D.O. monitor supplied, a mounting kit shall be provided. Mounting assemblies shall attach to standard handrails and shall support the D.O. monitor above the handrail so that the LCD display is 4-5 feet off the grade level. Mounting supports shall be aluminum and all hardware to fasten the supports to the handrail and to fasten the monitor to the supports shall be supplied with the kit. All hardware shall be stainless steel.

Mounting bracket assemblies shall be supplied to securely mount D.O. sensors to handrail as shown in the drawings. Mounting assemblies shall be aluminum with stainless steel hardware with sensors mounted directly to 1" aluminum or PVC pipe supplied by the contractor. Mounting assemblies shall be of a simple drop-on design to allow sensors to be lifted from the tank without the use of tools.

AUTO-CLEAN OPTION: A complete high pressure air supply system shall be integrated into the D.O. monitor enclosure. The air supply shall include as a minimum a compressor, check valve, air accumulator, and solenoid valve. Units with separate compressor systems shall be supplied with the air supply and D.O. monitor mounted in one enclosure to reduce installation costs, with all interconnecting wiring completed at the factory so that only AC power and sensor connections are required by the installer. Systems that do not include an air accumulator to insure adequate pressure bursts are not considered “equal” to the specified unit. The cleaning function shall operate automatically at the interval determined by the operator. In addition, the cleaner may be energized at any time using the switches on the front of the monitor. In operation, the cleaner system shall delivery short, high pressure bursts of air directly across the membrane. The number of air bursts during any one cleaning cycle shall be programmable by the operator to adjust for particular plant conditions.

The complete Dissolved Oxygen Monitor shall be Series Q45D/60 Optical as manufactured by Analytical Technology, Inc. or approved equal.