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R
OUTINE
S
ERVICING
748250-L Rosemount Analytical October 1999
6-11
Model 880A Non-Dispersive Infrared Analyzer
6.8.7 A
DAPTER
B
OARD
(DWG 624127)
The adapter board which includes a circuit breaker is used for line power distribution.
The adapter board also serves as an interface board for all the option boards and
provides the recorder output on TB2.
6.8.8 M
ICRO
B
OARD
(DWG 623782)
The Micro Board is a self-contained circuit assembly which includes an advanced
microprocessor and multiple I/O functions with a complete analog domain consisting of
analog-to-digital converters and digital-to-analog converters. Multiple output registers
allow the transmission of digital data to and from the board under program control. The
circuit board can be used alone or in conjunction with I/O boards that satisfy special
interfacing requirements such as the following:
1. Current output
2. Bi-directional remote range change board
3. Dual alarm assembly
4. Auto ZERO/SPAN
5. Calibration Gas Control
The microprocessor is configured with various memory arrangements depending on
the application: RAM, PROM, EEPROM. The 64K memory is available for all memory
functions. A selective arrangement allows rotating memory on specific boundaries.
The board is configured with an analog domain that allows the processing of analog
signals directly with a 12-bit plus sign ADC. In addition, two independent DAC's, each
12 bytes wide, allow the presentation of analog voltages for peripheral functions
immediately.
6.8.9 C
ASE
H
EATER
T
EMPERATURE
C
ONTROL
B
OARD
(DWG 624003)
This is a proportional temperature controller, which works on a variable time method.
Resistors' R7, R8, R9, R10, R11 and the sensor form a bridge which feeds a
comparator, AR1. AR1 operates in an ON/OFF mode to drive transistor Q3. The
sensor is a resistor with a positive temperature coefficient (1.925 ohms/
°
C).
The resistance is 500 ohms at 0
°
C. Resistors R1 through R6, Q1, Q2 and C1 provide
the circuit for the time proportioning action; C1 charges until the voltage on C1 reaches
9.0 V. Q1 then discharges C1, and the charging process repeats itself. The emitter of
Q2 follows the voltage on C1, which is essentially a sawtooth. This is injected into the
bridge, which causes the setpoint to bump on a variable time basis. Q3 (Through LED
CR1) triggers optical coupler U1 which gates TRIAC (U2). U2 allows fullwave VAC to
flow through the case heater element.
6.8.10 D
UAL
A
LARM
/C
ALIBRATION
G
AS
C
ONTROL
B
OARD
(DWG 624204)
This board is used for both dual alarm and calibration gas control, depending on the
position of the jumper in the jumper-selectable address. This is a peripheral circuit
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