August 2020
Reference Manual
L231040 Rev AD
22
Section 8: LTM-350 in a SIS
8.0 General Safety Guidelines
The LTM-350 transmitters are designed to output a
4/20mA
output
signal
under
normal
operation
representing liquid level in a vessel. The 4/20mA output is
considered the safety function of the transmitters.
The LTM-350 transmitters are design to operate without
the need for periodic maintenance or inspection. If the
LTM-350 transmitters are being used as part of a Safety
Implemented System (SIS) then periodic proof testing will
be required for the transmitter to detect any potential
failure which is defined as Dangerous Undetectable in the
transmitters' normal operation.
Proof Testing must be performed at regular interval of 1
year. The result of this testing must be documented. If the
transmitter exhibits a failure mode output during normal
operation then it will be necessary to perform proof testing
regardless of scheduled intervals.
8.1 LTM-350 Safety Ratings
1.
The Safe Failure Fraction: 92.46%
2.
The average Probability of Failure on demand is:
1.19 x 10¯³
3.
Executes diagnostics at a maximum interval of 1
sec.
4.
Provides a diagnostic/ failure update in less than 2
seconds of the occurrence.
5.
The transmitter may only be used in an SIS when:
•
Software Revision is 1.01.16 or greater
•
Hardware Revision is 1.00.02 or greater
6.
It is classified as Type B equipment.
7.
The transmitters must be used within the limit
defined in this manual.
8.
The maintenance, troubleshooting and safety
inspection should be done by qualified personnel.
The qualifications include but are not limited to
knowledge of the products operating principles,
application in which the transmitter is being
utilized, the information in this instruction manual
and a general knowledge/experience as an
Instrumentation or Electronic Technician.
8.2 LTM-350 Proof Test
1.
To avoid any false alarms take appropriate steps to
notify control room that the instrument is being
tested.
2.
Utilize the pushbuttons and scroll through the
main menus until "TestLoop" is shown.1
3.
Enter into this menu and modulate the current
output from 3.5 to 20.8 mA while verifying the
current output with a multimeter or the control
room. If this function does not work then
instrument is in Failure Mode. Use troubleshooting
tips to figure out why instrument is in failure mode
and do not try to recalibrate.
4.
Exit "TestLoop" function by pressing enter.
Notes:
The "TestLoop" function helps test for power
supply problems such as not enough voltage or
possible quiescent current related failures.
8.3 Safety Inspection
The LTM-350 transmitters have 3 major components the
magnetic float, the electronics (analog output) and the
sensor probe. The LTM-350 detects the magnetic float
position from inside the MLI (MLI - mounted) or along its
sensor (Direct Insertion). To work properly the float must
move freely either inside the MLI or along the sensor. If
the float is damaged or gets stuck in the vessel or along
the probe the transmitter will continue to report the
level/position of the float. This qualifies as a Dangerous
undetected failure. To avert this failure the float will need
to be inspected for integrity and movement. Depending on
the application some MLI’s can have two floats inside the
chamber and some transmitters can have two floats on the
sensor. In both cases the following inspection should be
done for both floats.
For MLI - mounted transmitters:
1. Remove the float from the level gage chamber and
visually inspect for damage such as dents or visible holes.
2. The float can be checked for leaks by submerging it in
water and observing for air bubbles.
3. Install the float inside the chamber (note orientation of
float) and move the float from bottom process connection
(0%) to the top process connection (100%) length of the
chamber using process fluid or other media. The float
should move freely from 0 to100%.
