Operational Theory |
| |
|
|
|
System power is supplied from a universal power supply module designed to be compatible with any international power source. Figure
The signal processing electronics including the microprocessor, analog to digital, and digital to analog converters are located on the motherboard at the bottom of the case. The preamplifier board is mounted on top of the motherboard as shown in the figure. These boards are accessible after removing the back panel. Figure
In the presence of oxygen the zirconia sensor generates a current. A current to voltage amplifier converts this current to a voltage, which is amplified in the second stage amplifier. The output from the second stage amplifier is sent to an 18 bit analog to digital converter controlled by the microprocessor. In the block diagram only one sensor is shown, but in reality there are three separate amplifier circuits for each sensor. The output of each sensor is then multiplexed to the analog to digital converter.
The high operating temperature of the ZrO2 sensor is required for proper operation of the sensor. The amplifier PCB contains a circuit that drives the heater embedded in the sensor. The voltage across the heater rises slowly to avoid damaging the heater/sensor assembly. After a few minutes, the sensor will be at the proper operating temperature.
The digital concentration signal along with input from the control panel is processed by the microprocessor, and appropriate control signals are directed to the display, alarms and communications port. The same digital information is also sent to a 12 bit digital to analog converter that produces the
Signals from the power supply are also monitored, and through the microprocessor, the system failure alarm is activated if a malfunction is detected.
Teledyne Analytical Instruments | 10 |
