Service manual

Section - VI Reading Station BT3000 PLUS Rev. 0, Soft Ver. 8 Page 9 of 12
The same µP552 utilizes two analog inputs for reading the temperature of the
cuvette plate and the vacuum level of the vacuum pump system. The U8A
temperature chip and U8B pressure chip amplify the analog signals of the
sensors. The µC764 is dedicated to the control of cuvette plate motor and the
linear actuator of the washer module. The U2 chip is a Programmable Array Logic
(PAL) device programmed for generating the complex quantity of logic gates used
for interfacing the photometer preamplifier with the µP552. The µC764 also uses
this gate for connecting to the Master Power Board (15-04209-01) described
below.
The U3 chip is an isolated DC/DC converter, which powers the photometer
preamplifier. It regulates +5 Volt DC input voltage into a ±12 Volt DC output
voltage.
6-7. MASTER POWER BOARD (15-04209-01)
The Main Power Board (Figure 6-6) is the densest board of the analyzer. It
accommodates all the devices required to control the stepping motors, valves, etc.
for the reading station. However, for practical reasons, another µC764 has been
inserted to provide temperature control and regulation for the cuvette plate.
The circuit consists of a comparator connected to the temperature sensor, which
is inserted into the bottom of the cuvette housing. The U8 comparator output,
along with the U5 chip, regulates the switching which generates a variable voltage
in the terminals of the Peltier modules. One section of the comparator controls a
relay for inverting the polarity when the ambient temperature requires momentary
cooling of the cuvettes system.
The process just outlined produces a relatively coarse temperature regulation of
approximately ±1°C. The fine regulation of ±0.1°C is performed by the software
implemented in the µP552. When monitoring the temperature of the sensor, the
above-mentioned regulator allows a continuous adjustment of the selected
temperature.