Chapter 2 Circuit System
12
Fluorophos® ALP Test System Model FLM300 Service Manual
Precision Voltage Reference: A 2.5V precision reference
IC generates the 2.5V signal used by the PMT signal
conditioning circuit, the PIC18’s analog-to-digital
conversion module, the digital-to-analog converters, and
the heat sense and conditioning circuits.
PMT Signal Conditioning Circuit: This two stage circuit
first converts the PMT’s signal input current to a voltage,
and then inverts and amplifies this voltage, both about a
virtual ground reference point through discrete logic. A
PMT input current of one microamp results in a 761
millivolt output swing.
PMT Analog-to-Digital Signal Conversion: The
conditioned PMT output voltage is read by an analog-to-
digital IC to 17-bit resolution against a 2.048 voltage
reference internal to the IC (16 microvolts, or a PMT
current of 20 picoamps, per count).
Thermistor Signal Conditioning Circuits: The 2.5 V
reference signal is used to generate a voltage across
each of the three thermistors used for heater regulation.
Each voltage is conditioned and amplified to the
appropriate range for digital conversion in the PIC18.
Digital-to-Analog Converters: Digital-to-analog
converters are used to set the PMT’s high voltage control
signal, the current through the cuvette and sample
illumination LED heaters, and the sample illumination
LED.
Temperature Sensor: An IC monitors the temperature of
the application PCB.
I/O Ports: Circuits on the application PCB interface the
80C186’s two serial ports (RS-232 and barcode) to the
back panel PCB. Circuits also interface to the
instrument’s parallel printer.
Application Logic: The application interface logic
consists of a programmable logic device (PLD) and two
octal D-latch ICs. This logic provides software accessible
hardware registers, enabling the software to read the
keypad (polled in a row/column process) and door
switch, manipulate the display, printer, keypad LEDs and
speaker, and interface to the RS-232 ports.
Connectors: Connectors are supplied for the processor
PCB, display, keypad, printer, power, fan, optical bench
components, incubator, and back panel I/O ports.
Serial (RS-232) Port Interface: An RS-232 line driver/
receiver provides the microprocessor with a serial port
interface that supports both hardware and software
handshaking.
2.5 Other Circuit Components
Optical Bench: The optical bench contains a sample
illumination LED and heater, excitation optics including a
440 nm band pass filter, heated cuvette sample holder,
550 nm long pass emission filter with solenoid driven
shutter, and a photomultiplier tube (PMT) and socket. All
electronic elements connect to the application PCB. The
PMT socket internally generates the PMT’s high voltage
supply from 15 VDC and a 0-5V control signal.
FL2168PC LED PCB: This PCB is mounted to the optical
bench and contains the sample illumination LED and a
chip thermistor.
Fan: An exhaust fan is mounted on the back panel of the
instrument, behind the power supply.
PCB105 Back Panel PCB: This PCB is mounted to the
back panel of the instrument and provides RS-232 and
barcode ports.
The DB-9 RS-232 port conforms to the DTE RS-232C
standard and has the following pin assignments:
Signal Pin Direction
Receive Data 2 to FLM300
Transmit Data 3 from FLM300
Data Terminal Ready 4 from FLM300
Signal Ground 5 common
Data Set Ready 6 to FLM300
Request to Send 7 from FLM300
Clear to Send 8 to FLM300
Note that your instrument is only designed to support
unidirectional communication with an external device. At
this time, there is no protocol for bidirectional
communication. For a sample RS-232 Port Setup, please
see the RS-232 Supplemental Information in the
Appendix at the end of the instrument’s user’s guide.
NOTE: This instrument requires the use of a null modem
RS-232C cable. There are several variations of null
modem cables. Advanced Instruments
recommends that you purchase a RS-232C cable
direct from our factory.
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