Principle Of 902; Measuring Principle; Operation Of Mechanisms; Reaction Cuvette Rinsing And Water Blank Measurement - Hitachi 902 Service Manual

4.2

Principle of 902

4.2.1 Measuring Principle

The measuring principle of the 902 will be explained by dividing it into operation of
mechanisms, analytical flow, and operating position.
(1)

Operation of Mechanisms

The 902 consists of sample disk, sampling mechanism, reagent disk, reagent pipetting
mechanism, reaction disk, reaction bath, stirring mechanism, rinse mechanism,
photometric system, touch screen type LCD, etc. The analytical operation will be
explained with reference to the 902 system configuration in Fig. 4-1.
(a) Set sample cups or test tubes containing sample on the sample disk and reagent on
the reagent disk. Also set the test items requested for the samples plus the
measurement conditions on the LCD. At the start of analysis, the operations below
will be carried out automatically.
(b) Reaction cuvette rinsing and water blank measurement
The reaction cuvettes are rinsed, and the absorbance of the cuvettes (containing
water) is measured four times. The measured value becomes the water blank value
for each cuvette. After completion of the water blank measurement, the water is
aspirated from the cuvettes.
(c) Sampling
After water blank measurement, the reaction cuvette rotates to the sample pipetting
position, the sample disk turns and the sample cup or test tube containing sample is
brought to the sampling position. The sample probe then moves to above the
sample cup or test tube, and descends into it. A liquid level sensor is attached to the
probe, which stops the probe descent when the tip of the probe contacts the surface
of the sample. The necessary volume of sample for analysis is aspirated by the
sample pipetter. The sample probe then moves to above the reaction cuvette at the
sample pipetting position and descends until the probe tip reaches the bottom of the
cuvette, whereby the sample is discharged. Thereafter the probe moves to the probe
rinse bath where its inside and outside are rinsed with deionized water.
(d) 1st reagent addition and stirring
When the reaction cuvette containing discharged sample stops at the 1st reagent
adding position, the reagent pipetting mechanism aspirates the required volume of
reagent. Then the reagent probe moves to above the reaction cuvette and
discharges the reagent. A liquid level sensor is also attached to the reagent probe,
which stops the probe when its tip contacts the surface of the reagent. The
necessary volume of reagent is discharged by the reagent pipetter. After the reagent
discharge, the probe moves to the probe rinse bath where its inside and outside are
rinsed with deionized water. After the 1st reagent addition, the reacting solution is
stirred by the stirring mechanism. And after the stirring, the stirring rod is thoroughly
rinsed with the rinse water.
(e) Photometry
After addition of the 1st reagent, measurement of absorbance of the reacting solution
starts. The absorbance during the reaction is measured at 18-second intervals.
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