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SMC sierra monitor corporation Sentry Instruction Manual - Version 6
SERVICE
Page: 63
7.3 COMMUNICATIONS
7.3.1 DESCRIPTION OF COMMUNICATIONS
The Sentry controller scans each channel in turn taking
less than one second to scan all channels. At each
channel:
1. A "reset" signal is sent out to clear all module
communications.
2. An address (which is a module number) is sent
out and the controller waits for a response. The
response is a digital frequency which is
proportional to the first of eight parameters
which are interrogated by the controller.
3. Because the controller received an answer and
knows that the particular module is on that
channel it continues to interrogate that module
to retrieve the remaining seven parameters
before moving to the next module number.
The eight (total) signals are:
• Value of Ground.
• Value of sensor signal (relates to gas
concentration).
• Heater voltage (Type 1 Module) or
Bridge Voltage (Type 2 Module).
• Heater current (Type 1 Module) or
Bridge Current (Type 2 Module).
• Sensor type (Type 1 through 4
Modules).
• Calibration switch condition on/off.
• Module voltage (tests line drop from
controller to module).
• Reference voltage (used together
with ground to ratiometrically
compensate for any temperature drift
in module components)
The controller interprets the information received during
the polling and takes actions as necessary. (Any deviation
from normal is rapidly validated to avoid errors due to
electrical noise.) The information, combined with
continual system diagnostics allows the controller to
accurately determine abnormal conditions. Table 7-1
provides a categorized listing of Sentry messages.
SYSTEM ERRORS MODULE ERRORS WARNING/STATUS MESSAGES
E-01 (ROM Check Failed) DISCONNECTED NO MODULE
E-02 (RAM Check Failed) CHECK POWER ADJ MODULE OFF
TIMER FAILURE MODULE VOLTAGE LOW WARM-UP WAIT - 00:00
CLOCK FAILURE SENSOR FAILURE FACTOR MISSING
DUPLICATE MODULE UNCALIBRATED
CHK BRIDGE VOLTAGE REPLACE SENSOR
TYPE ERROR CALIBRATION OVERDUE
REPLACE BATTERY
CALIBRATION SWITCH ON
DIAGNOSTIC SCAN
FAST ERROR CHECK
LOW SENSITIVITY
NOT CALIBRATED
CALIBRATION ABORTED
Table 7-1
Sentry Error and Diagnostic Messages