Mindray BS-120 - Photometric Unit; Introduction; Components of Photometric Unit

4 Units Description
4-26
then loosen two M4x8 hexagon socket set head screws to remove the lever from
the motor.
2. Remove the motor support which is fixed to cam board by two M4x6 and two M4x8
hexagon socket head screws allocated with spring pads, and then take out the
shaft ring.
3. Remove one M3x8 hexagon socket head screw allocated with spring pad and plain
pad, and then take out the output shaft and cushion.
4. The sensor is fixed to bolt by two M3x6 hexagon socket head screws; remove the
sensor by loosening the two screws.
Precautions:
1. The motor shaft should protrude the plane of lever about 3mm while installing the
lever.
2. Place the plug of stepping motor faced down while installing the stepper motor.
3. Remove the cables before performing above steps.
4.6 Photometric Unit
4.6.1 Introduction
Chemistry analyzer is a typical instrument which features in optics，mechanics, electronics
and arithmetic. The photometer is one of the key components of the instrument and
determines directly the precision and accuracy of measurement of the system.
The light source irradiates directly the cuvette in the photometer. A combined light passes
through an optical interference filter and turns to a monochromatic light. The
monochromatic light passes through the cuvette and is received by the photoelectric
detector and then is converted into an electrical signal by the photoelectric detector. The
microprocessor calculates the concertration of the solution in the cuvette by contrasting
the optical intension of the light before and after passing through the solution. The multiple
monochromatic wavelengths in the pototometer system are obtained by utilizing the filter
wheel. Rotate the filter of a specific wavelength to the light path while performing the
colormetric measurement.
4.6.2 Components of Photometric Unit
The lens 1 converges the light beam emitted from the light source to the filter. The lens 2
collimates the monochromatic light beam aimming to the reaction cuvette. The light is
absorbed when passing through the solluton and then is converged at the photodiode via
the lens 3. Finally the photodiode converts the light signals into electric signals and then
outputs them. From the outside to the inside of the reaction disk, the whole configuration
of the light path is shown in Figure 4-29.