Advanced Instruments 4250, User Manual

Page: 35 / 121

13
Instrument Operation
Measurement and control circuits (inside)
The microprocessor-controlled circuits automatically measure and con-
trol the dynamic temperature of the sample freezing chamber. Process
calibration data and sample temperature information. They also present
calibrated test results on the digital display.
Electronic circuits (inside)
The main circuitry is contained on two printed circuit boards in a moth-
erboard/daughter board configuration. More in depth technical details
are available in the unit service manual sold separately.
Processor Board: The processor board is the smaller of the two printed
circuit boards and contains the Intel 80C186EB central processor, two
flash EPROM’s, RAM, Realtime clock, watchdog circuit, and glue
logic.
Application Board: The application board contains the circuits for con-
trolling and interfacing with the other subsystems such as the keypad,
display, head motor, cooling assembly, RS-232, printer and barcode
ports, etc. The application board also contains two 20-bit A/D convert-
ers for reading the sample and block probe thermistors.
Display panel (Figure 5, Item 4)
The display panel displays:
• Test status and results.
• Status messages when the instrument is turned on or when functions
are selected.
• Pertinent error messages when fault conditions occur. (Messages
longer than 20 characters scroll across display.)
Keypad (Figure 5, Item 4)
The keypad allows operator input to the microprocessor. For the layout
and functions of the keypad switches, please see Figure 6.
Printer (Figure 5, Item 9)
The printer records on paper the displayed test results, sample identifi-
cation, and other necessary information. Messages longer than 40 char-
acters are wrapped around to the next line.