Part No. 715-0088, Rev. B
- 30 -
3.9. General Features and Operation
3.9.1.
Microprocessor
The AeroNOx 2.0 is designed around the TEKMOS TK68HC711E9CFNE3
microprocessor operating with a clock frequency of 3MHz. The microprocessor
and associated software are responsible for the NO and NO
2
analysis operations
and the delivery of NO. Firmware may only be updated by International
Biomedical.
3.9.2.
4.3 Smart LCD
The display is a smart 4.3 LCD that contains graphics and subroutines called by
the TEKMOS processor. The display may only be replaced. Attempting to access
the USB port may harm the device and render it inoperable.
3.9.3.
Startup
The AeroNOx 2.0 is turned on by pressing the power switch on the front panel.
Activating this switch awakens the microprocessor from its sleep mode. A
battery voltage and a Read only Memory (ROM) check are performed. If all is
well, the microprocessor (U7) activates the LCD display with a message
containing the model and the current software version showing for about 4
seconds, then defaulting to delivery mode where flow rate and concentrations of
NO, O
2
, and NO
2
are shown. The SYS_ON signal is also fed to the power
supply circuit board, enabling transistor Q1, which now pulls U3-2 low. This now
takes the regulator U3 out of shutdown, bringing the main +5 volt supply online.
At this point, the instrument is completely powered up and functioning, the O
2
and
flow displays are on, and the sample pump has started and is running.
Holding down the front panel power button will turn the unit off. When the unit is
off, portions of the instrument are still powered up but the microprocessor is put
into a sleep mode. Power is still applied to the microcontroller, the power button
circuit, the Analog to Digital converters, and to the analog power supplies. The
Analog to Digital converters are in a power down mode with very small current
consumption when the instrument is off. In addition to some circuits on the control
board, the analog power supplies also support the sensor board. Power is
required to maintain a bias voltage of -300 mV on the NO sensor. If this bias is
lost, several hours are required before the NO sensor can be used to measure
gas accurately. More information on the sensors is provided later in this manual.
Maintaining the bias on the NO sensor means the instrument is ready for
calibration and use immediately upon powering up. The NO
2
sensor does not
require this constant bias when the unit is off; instead, a set of contacts on the
power switch close when the switch is turned off, placing a short circuit across the
SENSE and REFERENCE electrodes of the cell. This keeps the NO
2
sensor in a
ready-to-use condition.
On the power supply board, U3 remains powered, although U3 draws little current
in its shutdown condition. If the external DC supply is connected, the associated
charge circuit and VDC regulator (U8) will function regardless of unit power state.
Summary of Contents for AeroNO 2.0
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