ABB MT series, Руководство пользователя

Страница: 8 / 15

8
4 Safety information for inspection and
maintenance
Corrective maintenance work may be performed only by trained
personnel.
The MT5000 will operate normally without the need for periodic
maintenance or inspection. If the transmitter meets or exceeds
the requirements of the application, the transmitter can be ex-
pected to provide reliable level indication for a minimum of 10
years.
If the MT5000 transmitter is being used as part of a Safety Im-
plemented System (SIS), periodic testing will be required to
proof the transmitter and detect any potential failure which is
defined as Dangerous Undetectable in nor-mal operation. Proof
testing must be performed at regular intervals (2 years) and the
results of this testing must be documented. Should the trans-
mitter exhibit a fault during normal operation, it will be neces-
sary to perform the proof testing regardless of schedule. As part
of the testing documentation, all parameters included in the
menu structure of the transmitter (see page 10) as well as the
configuration of the module jumpers (see page 9) must be rec-
orded. The transmitter is capable of supplying (1) 4-20mA out-
put. If a transmitter is equipped with more than one indication,
only the process variable selected by the PV= menu option will be
considered as a safety function as this selected variable will be
the basis for the 4-20mA output. The MT5000 transmitter may
only be used in a safety-related system when the mode of that
system is low demand. As a device, the MT5000 transmitter will
be used to provide a level measurement to prevent overfill and
dry run of a vessel.
If a transmitter fails an inspection or assistance is required for
inspection or troubleshooting, contact the Service Department
at ABB via e-mail at service@ca.abb.com. The Service Depart-
ment will answer questions, provide additional assistance, and
issue Return Authorization Numbers for equipment in need of
repair.
CAUTION: In the event a guided wave radar transmitter has suf-
fered a failure in any component which is exposed to the pro-
cess, any other guided wave radar transmitter installed in the
same or similar process should be inspected for the same failure
regardless of its maintenance schedule. These Common Cause
Failures include: 1) Damage to the high frequency coupler, 2)
damage to the electronics module, 3) deformation of the sensor
probe due to process agitation.
Notes on usage in Safety Instrumented Systems:
1) The MT5000 performs internal diagnostics at a maximum
interval of 15 minutes.
2) The MT5000 will provide annunciation of a diagnostic failure in
less than 15 minutes of the occurrence.
3) The failure of any internal diagnostics will result in noti-
fication of the fault by setting of diagnostic bits in HART
protocol output.
4) All MT5000 FMEDA analysis is based on using a safety
accuracy of 2%.
5) The internal diagnostics are designed to achieve a Safe
Failure Fraction of 90% minimum.
6) The target average probability of failure on demand is less
than 1.5 x 10
-3
.
7) MT5000 transmitters are qualified for use in a SIS only when
the output used for the safety function is the 4–20 mA output.
8) If MT5000 transmitters equipped with HART are used in a SIS,
they must be fitted with a 4–20 mA output HART Protocol/M7A
or M7B and running software version 090414.00.001 Electronic
Module or higher.
4.1 Personnel Qualifications
Safety Inspection, Maintenance and Troubleshooting should only
be performed by qualified personnel. These qualifications in-
clude a knowledge of the information in this instruction manual,
knowledge of the product and its operating principles,
knowledge of the application in which the transmitter is being
applied, and general experience as an Instrument Technician.
Before, during and after performing Safety Inspection, Mainte-
nance or Troubleshooting it will be necessary to observe and
adhere to any safety standards, practices or requirements de-
fined in the policies of the end user.
4.2 MT5X00 Alarm Levels and Dangerous Undetected Failure
Rates Calculation
The MT5X00 Dangerous Undetected (DU) failure rates calcula-
tion are based on the choice of either 3.61 mA or 21 mA alarm
current levels, depending on the user’s preference. The value
should be selected on the basis of which reflects the direction
the output signal would tend toward when a trip is required.
4.3 Alarm Levels to be Programmed in Logic Solver
It is strongly recommended to the user that the Safety PLC soft-
ware should be configured to detect fail-low (e.g. ≤ 4 mA) and fail
-high (e.g. ≥ 20 mA) inputs as an alarm value and possibly as re-
quiring a trip, in addition to the explicit use of 3.61 mA or 21 mA
(the selected output value when the diagnostics detect a failure).
This precaution allows the user’s PLC to detect failures such as
open and short circuits that cannot be detected by the MT5000
diagnostics. The corresponding failure rates this detects are 68
FITs and 73 FITs respectively.
4.4 Use of Critically Restricted (CR) Mode for Safety
Instrumented Systems Applications
The HART version of the MT5100 has an operation mode for level
and interface measurements which is named the Critically Re-
stricted mode. This mode is only accessible through a HART
command on the MT5100 in the “Extended Setup/Advanced
Setup/CR Read Mode” menu.
The Critically Restricted (CR) mode shall not be used in a Safety
Instrumented System.
4.5 Required Tools
The following tools may be required to perform inspection,
maintenance or troubleshooting of the MT5000 transmitter.
- Crescent Wrenches or box end wrenches
- Screwdrivers
- Hex Key Wrenches
- Calibrated Digital Multi-meter
- Tape Measure