METRON QA-IDS, User & Service Manual

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verters, which are run from a register connected to the data bus. The
inputs are protected against overvoltage.
6.4 Serial Port
The serial port has a 9-pin D-sub male (DTE), and is connected to a
PC with a null modem cable. The handshake is carried out in the
software. The control signals RTS, CTS and DTR are connected on
the D-sub contact.
6.5 Microprocessor
The microprocessor unit consists of a Motorola processor with a
clock frequency of 16 MHz, RAM, A/D converter, watchdog,
real-time clock, parallel and serial I/O. The program is stored in a
128K RAM with battery backup. The setup parameters and calibra-
tion data are stored in EEPROM in the CPU. The LCD display and
keypad are connected to the processor's bus via registers. The
built-in A/D converter in the CPU is used to monitor the tempera-
ture and battery voltage.
6.6 Pressure Gauge
The pressure gauge consists of a differential pressure sensor, a mea-
surement amplifier, the reference voltage and an instrumentation
amplifier.
The pressure sensor, U1B00, is made up of a piezo-resistive element
encapsulated in silicon. It is temperature- and offset-compensated. It
receives its voltage supply from the reference voltage. The output
signal is amplified with an instrumentation amplifier, U1B10, which
is a 4 x operational amplifier. The amplified signal is proportional to
the pressure measured, and is fed to a 12-bit A/D converter, U1700.
To measure negative pressure, an offset of 800 mV is inserted at
zero pressure. The offset is adjusted with R1 B1B. The amplifica-
tion is adjusted with R1B10 to 4050 mV at 1700 mmHg. The refer-
ence voltage is generated from V5P using a variable voltage divider,
R1B26, and an operational amplifier, U1B20. U1B20 is also used
for temperature measurement,
6.7 Pump
The QA-IDS has a pump from Saphierwerk, driven by a stepper mo-
tor. The pump is a rotating piston pump with the pump head and pis-
ton in artificial sapphire. It pumps 50 µl per revolution. The pump
has a circuit board with a Hall sensor to provide an index per revolu-
tion. The index is used to measure the volume pumped. The stepper
motor is a bipolar type with 200 steps per revolution.
6.8 Stepper Motor/Drivers
The stepper motors are run by three circuits from Ericsson. The
stepper motor driver U 1810 is connected to the CPU, and generates
the control signal to two driver circuits. The stepper motor can run
in full-and half-step mode. The driver circuits, U1820 and U 1830,
have built-in temperature protection and pulse width modulation to
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