YOKOGAWA EXA DO402G, Руководство пользователя

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<1. Introduction and General Description>
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IM 12J05D02-01E
The DO70G sensor operates based on the principle of optical (fluorescence) measurement.
The sensor comprises a fluorescent membrane, light-emitting part, light-receiving part, and
internal circuit.
An external power source is required. Oxygen molecules pass through the permeable membrane
to a fluorescent substance and shift the phase of fluorescent emission. The degree of this shift is
inversely proportional to the partial pressure of oxygen on the sample side, resulting in the output
of a current equivalent to the polarographic current adjusted by the internal circuit.
A temperature sensor is integrated in both sensors, and the temperature signals are used to
automatically compensate the measurements of dissolved oxygen.
The combination of air-saturated water calibration and zero calibration helps maintain the
performance of the instrument.
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Display functions and ranges
The display continuously gives you all necessary information at a glance. The process values are
shown in easily readable programmable units. Either mg/L. % saturation or ppm can be chosen.
The user-interface is simplified to a basic set of 6 keys accessible through the flexible window
cover. It uses a simple step by step, question and answer style to communicate with the operator
by giving messages on the second line of the display and indicating which keys are to be pressed
in the display.
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Automatic air calibration
Calibration for a dissolved oxygen instrument is performed by simple air calibration (please refer
to 6.3.1 section for the optical sensor).
Criteria for automatic calibration (stabilization time, DO values) can be set to suit the sensor.
In addition to the air calibration three additional calibration procedures can be used:
1. Span calibration using air saturated water
2. Zero calibration using sulfite saturated water
3. Process calibration using laboratory reference method
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Alarm and control functions
The EXA DO402 has four built-in relay contacts. From the factory the first two contacts are pre-
defined as a high or low alarm.
The third contact its pre-defined as a wash contact. This wash contact is driven by a wash-timer
with adjustable wash-time, interval time and relaxation time to control the wash cycle.
The fourth contact is fixed to function as an alarm, indicating that the EXA has found a fault in the
measuring loop. FAIL safe.
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Cleaning
In combination with the appropriate sensor and immersion type fitting the wash timer with
remote start possibility can be used. Interval-time, washing time and relaxation time are free
programmable.
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Damping time on output signal
Under certain circumstances disturbances can cause high peaks in the output signal. To avoid
these disturbances the EXA DO402 has an electronic filtering which averages the output signal
during a programmable period. This damping time is programmable between 0 and 120 seconds.
9th Edition: Aug. 05, 2015-00