Thermo 42i, Instruction Manual

Page: 232 / 314

System Description
Electronics
8-8 Model 42
i
Low Source Instruction Manual Thermo Electron Corporation
Temperature Control
Board
The temperature control board regulates and sets the temperature of the
reaction chamber and converter.
The reaction chamber temperature is measured with a thermistor. The
voltage across the thermistor is fed to the main processor for use in
calculating and displaying the reaction chamber temperature. The voltage
across the thermistor is also compared to a set-point voltage and used to
control that the reaction chamber heaters to maintain a constant
temperature of 50
°
C. Protective circuitry prevents over heating in the event
of broken wires to the thermistor.
The converter temperature is measured by a conditioned thermocouple
signal and fed back to the main processor to be used to display and control
the converter temperature. The temperature control board receives control
signals from the main processor software to control the converter heater to
the desired set point. Protective circuitry prevents over heating in the event
of broken wires to the thermocouple or processor faults.
PMT Power Supply
Assembly
The PMT power supply produces high voltage to operate the photo
multiplier tube used in the measurement system. The output voltage is
adjustable from approximately 600 to 1200 volts under software control.
Input Board Assembly
The input board accepts the current signal from the PMT and converts it to
a voltage, which is scaled by a factor of approximately 1, 10, or 100
depending on the full-scale range of the NO channel. The scaled voltage
signal is converted to a frequency and sent to the microprocessor.
The input board includes a test signal that can be activated under software
control. The test signal is injected at the first stage of the input board in
parallel with the PMT input. This allows the input board and the
connection to the processor system to be tested and calibrated without using
the PMT.
Digital Output Board
The digital output board connects to the motherboard and provides
solenoid driver outputs and relay contact outputs to a connector located on
the rear panel of the instrument. Ten relay contacts normally open (with
power off ) are provided which are electrically isolated from each other. Eight
solenoid driver outputs (open collector) are provided along with a
corresp24VDC supply pin on the connector.