4 Operation
Model 1220
4-14
Teledyne Analytical Instruments
4.10 FAIL Alarm Conditions
The possible FAIL Alarm Conditions are:
- A sensor fails.
- One of the power suppliers fails.
- 0-10V Output fails.
- The ADC times out without a proper end-of-conversion (EOC).
Whenever a failure is detected, the FAIL alarm is activated: the blue
LED turns on, the alarm relay is de-energized (the FAIL relay is FAIL-
SAFE, and the audible alarm is activated. The power supplies to both
sensors are disabled.
Failure alarms are accompanied with a FAIL code number. The
display alternates between “FAIL” and the code number.
The failure alarm may be bypassed (by pressing the Bypass Button),
in which case, the blue LED flashes, and the audible alarm is deactivated.
To acknowledge a failure condition, press RESET. This restarts the
instrument (as if the
button has been pressed twice). Alternatively, you
may turn the unit OFF using the
button.
NOTE: The reason the failure modes require restarting the instru-
ment is that once a failure has been detected, the unit should
not be used until the error is fixed.
When a failure alarm is detected, the other two alarms (caution and
high) are disabled.
4.11 Calibration of Combustible Gas Detectors to the
LEL of Gases other than Methane
The lower explosive limit (LEL) varies substantially between the
different explosive gases. It is, therefore, necessary to consider the LEL of
a particular gas as well as the relative response of a detector to this gas in
order to calibrate the detector to indicate the concentration as a percentage
of the LEL. The most commonly used calibration gas contains small