Dissolved oxygen (DO) is a liquid process measurement for determining the amount of oxygen dissolved or carried in the process liquid. There are three common technologies for dissolved oxygen measurements: polographic, galvanic and optical. The standard units of measure are milligrams per liter (mg/l), parts per million (ppm), parts per billion (ppb), or % saturation.
The FLEXA™ series analyzers are used for continuous on-line measurements in industrial installations. With an option for single or dual sensor measurement, they are the most flexible two-wire analyzer available.
What is a 4-Wire analyzer?
This terminology only refers to power supply of the analyzer. It does not have any reference to the number of wires. The 4-wire analyzers separate the power supply from the measurement output. As a minimum we need two wires for the power supply and two wires for the current output of the analyzer. FLXA402 has up to four analog outputs, one analog input, four digital outputs, one digital input, digital communication and of course the sensor input wiring. The advantage is that any functions are combined in one enclosure. Local control and alarm functions are possible. In small control installations this is a cost saving feature.
What is a 2-Wire analyzer?
The 2-wire analyzers commonly referred to as Analyzers combine the wires for current output, for power supply and digital communication. The FLXA202/FLXA21 combines the power supply with mA output and HART communication: all with only two wires plus shield. The advantage is safety (only 24VDC) and simple installation. Just two wires between control room and analyzer. This is an advantage in large scale operations where process control is centralized in the DCS system.
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