Oil in Water Analyzer | Operational Theory 1 | |
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what it was in the last scheduled zero calibration. This zero reading is set at zero. The Auto Zero circuit is a digital circuit, which employs a DAC (Digital to Analog Converter) that can go out of range.
When the threshold cannot be found (oscillation persists), this means that measuring and reference peak signals as viewed on the oscilloscope at the output of the second amplifier in the detector module are too far out of balance on zero fluid. When this occurs, you must initiate optical balancing of the optical filters for equal light transmission on zero fluid. Measuring and reference peaks must be within one volt with zero fluid in the cell.
Zero drift may occur in the following cases:
1.The output source changes or chemical or solid deposits form on the cell windows, but the application is such that interfering chemicals (sample background changes) are not a problem. The zero fluid in this case may be the major component of the sample, void of the component of interest. For oil in very clean water applications, the Zero fluid can be a hydrocarbon free air or N2.
2.The sample may contain chemicals that are not of interest, but absorb UV energy at the measuring wavelength used for analysis of the component of interest (for example, oil in water applications). These chemicals produce a signal that adds to the signal of the component of interest and makes it inaccurate. The Auto Zero system discriminates the two signals and drives the interfering signal of the background chemicals below zero on an hourly basis. The zero fluid in this case is the sample of which the component of interest is filtered out while the background chemicals are preserved. The Auto Zero system corrects for background changes on an hourly basis, if the analyzer is set to
1.5System Description
The photometric analyzer is constructed for hazardouz area (Models 6600,
Teledyne Analytical Instruments | Part II: |
