Teledyne 6600 - Manual (Page 69)

Part II: 1-5
Oil in Water Analyzer Operational Theory 1
Teledyne Analytical Instruments
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 N
2
.
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 Auto-Zero in an hourly basis.
1.5 System Description
The photometric analyzer is constructed for hazardouz area (Models
6600, 6600Z-divII or 6600X-div I) use and is mounted on a BACKPLATE, an
open rack, or in a closed cubicle.