Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 309)

Theory of Operation Teledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 309
B OX T EMPERATURE S ENSOR
A thermistor is attached to the motherboard. It measures the analyzer’s internal
temperature. This information is stored by the CPU and can be viewed by the user for
troubleshooting purposes via the front panel display (see Section 12.1.2).
13.4.5.4. ANALOG OUTPUTS
The analyzer comes equipped with four analog outputs: A1, A2, A3 and A4. The type
of data and electronic performance of these outputs are configurable by the user (see
Section 5.4).
O UTPUT L OOP - BACK
All four analog outputs are connected back to the A/D converter through a loop-back
circuit. This permits the voltage outputs to be calibrated by the CPU without need for
any additional tools or fixtures.
13.4.5.5. INTERNAL DIGITAL I/O
This channel is used to communicate digital status and control signals about the
operation of key components of the Optical Bench. The CPU sends signals to the
sync/demod board that initiate the ELECTRICAL TEST and DARK CALIBRATION
procedures.
13.4.5.6. EXTERNAL DIGITAL I/O
This External Digital I/O performs two functions: status outputs and control inputs.
S TATUS O UTPUTS
Logic-Level voltages are output through an optically isolated 8-pin connector located on
the rear panel of the analyzer. These outputs convey good/bad and on/off information
about certain analyzer conditions. They can be used to interface with certain types of
programmable devices (See Section 3.3.1.4).
C ONTROL I NPUTS
By applying +5VDC power supplied from an external source such as a PLC or Data
logger (See Section 3.3.1.6), Zero and Span calibrations can be initiated by contact
closures on the rear panel.
P OWER UP C IRCUIT
This circuit monitors the +5V power supply during start-up and sets the analog outputs,
external digital I/O ports, and I
2 C circuitry to specific values until the CPU boots and the
instrument software can establish control.
13.4.6. I 2 C DATA BUS
I 2 C is a two-wire, clocked, bi-directional, digital serial I/O bus that is used widely in
commercial and consumer electronic systems. A transceiver on the motherboard
converts data and control signals from the PC-104 bus to I
2 C. The data is then fed to the
relay board, optional analog input board and valve driver board circuitry.