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© 2021 All rights reserved. Data subject to change without notice.
LPT - Operation Manual
Rev. E | 2021.03
during the warm up period. This is normal and the length of time the gas alarms exist is dependent
upon the length of time since the unit was last powered up and the state of the environment it
is installed in. After warm up the green power LED illuminates continuously indicating normal
operation.
6.7.3 Open Loop
If the 4 - 20 mA signal loop has not been connected properly or has been damaged in some
manner between the analog transmitter and the device to which it is sending its signal output,
the LPT will not run or function at all. At this point, the wiring should be inspected for potential
problems.
7 OPERATION
7.1 System Operation
Normal operation is indicated by a solid light on the external LED. During normal operation, the
gas level will be reported through the current loop, and a rough reading can be obtained from
the voltage test points. The LED will remain solid when the device is in working order, and is not
aff ected by gas concentration.
7.2 Fault Detection
The LPT has built in fault detection, and in the event of a problem with the measurement circuitry
the transmitter will indicate a fault condition by fl ashing the external green LED (short OFF and
long ON time). At this point, the transmitter will output approximately 3.5 mA on the current loop
and the test points will alternate between 0 and 1 volt every second. Normal operation will resume
once the fault condition has been r
ectifi ed.
NOTE:
While faults in the circuitry can be detected, a dead or damaged sensor will usually appear
to the transmitter as a zero gas reading. To ensure safe operation, periodic bump tests are required.
