New Oxygen Measurement System Featured
The latest edition of the Danfoss Evita? oxygen measurement system will be on display at the Water Environment Federation Technical Conference. The Oxy 4100/4150 monitors feature a 4-20 mA HART? data transmitter mounted behind the oxygen sensor and temperature sensor in the floating ball.
Up to 15 of the transmitters can communicate via a single 2-wire connection to a PLC or SCADA system using the HART? communication multi-drop mode to transmit oxygen concentrations, information on temperature, remaining sensor life, and alarms, including type of error.
Since there can be large fluctuations in the oxygen concentration in various areas of an aeration tank, several sensors may be installed in each tank to provide an oxygen profile. The benefits are energy savings and a process better tuned to fluctuations in the BOD load. A long sensor cable allows up to 1,000 meters between a transmitter and PLC/display.
The Oxy 4100/4150 transmitters can be set up for communication with either a PLC or a USC 5000/6000 signal converter. Adding signal converters allows access to local readouts and enhanced accuracy thanks to a built-in pressure transmitter. Also, the signal converter is a precondition for installing and changing different communication buses.
The communication module snaps into place at the bottom of the signal converter without the use of tools. It can be changed when new communication protocols are developed. For the time being Profibus modules are supplied, but new modules will be developed according to the standards approved by the market.
The Evita sensor design includes four fins, which improves the self-cleaning effect. Sensors may be wiped clean with a cloth. Sensor replacement can be performed in five minutes. Operators simply unscrew the collar holding the sensor in place and insert a new sensor. Spare sensors can be stored for an unlimited time and only start to operate when connected to the transmitter.
Sensors have a typical operating life of 2-3 years, thanks in part to a half-meter of silver wire applied to the surface area of the anode, enlarging it as much as possible.
The sensor has automatic calibration. By pressing a button, the system calibrates itself within minutes. Alternatively, the same effect may be obtained by simply tilting the transmitter. A tilt switch will initiate the calibration routine.