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Logix 3400MD Digital Positioner FCD LGENIM3404-00 – 9/09
flowserve.com
7.15.1 Initiating a Valve Signature
A feature of the Logix 3400MD positioner is the ability to capture and
store a valve diagnostic signature. A signature is the collected data
response of the valve to a predefined set of operating conditions. This
stored data can later be uploaded to the host system for analysis of
potential problems. By comparing a baseline signature, when the valve
is new, to subsequent signatures at later times, a rate of change can be
tracked which can help predict possible faults in the valve before they
happen. This is called ‘predictive maintenance’. It is important to note
that the purpose of the positioner is to act as the data acquisition device
for the signature. Analysis of the data is not done on the device, but in
the supervisory system.
NOTE:
Signature data is lost if the positioner is reset or if the power is
cycled
7.15.2 System Preparation
0
WARNING:
By definition, the collection of the signature
requires the unmanaged operation of the positioner. Therefore,
the process must be in a safe operating mode where unex-
pected movement of the valve will not cause a hazardous
condition.
Before a valve signature can be run, the Transducer Block must Out-of-
Service (OOS).
7.15.3 Signature Procedure
The following steps are an example of how to initiate a ramp signature
capture.
1. Make sure the process is in safe condition and notify the control
room that the valve will temporarily be taken off-line.
2. Verify preparedness to proceed.
3. Put the Transducer block MODE_BLK OOS
4. Set SIG_START to desired value.
5. Set SIG_STOP to desired value.
6. Set SAMPLE_TIME to desired value (typically 0.3).
7. Set SIG_RATE to desired value (typically 20).
8. In SIG_FLAGS select; RUN_RAMP.
9. In SIG_FLAGS, select RUN/BEGIN_SIG.
10. Write value to the Logix 3400MD digital positioner.
11. The valve will stroke to the beginning position, as defined by
SIG_START and will begin ramping to the desired ending position,
as defined by SIG_STOP.
Notice that the valve will move and FINAL_POSITION_VALUE will
change.
12. SIG_FLAGS indicates SIG COMPLETE.
13. Return the MODE_BLK to auto.
14. Notify control room the valve is back on-line. The stored signature
will remain in the Logix 3400MD digital positioner RAM until the
either the unit is powered down, or another signature is taken
which overwrites the previous one.
7.16 Step Signature
If a step signature was desired, simply do not select STEP_RAMP
in SIG_FLAGS, and then set the SIG_HOLD prior to selecting RUN/
BEGIN_SIG.
NOTE:
SIG_RATE has no effect on Step Signature.
7.16.1 Collection of Stored Signature
The collection of the stored signature is accomplished by the host
system. It is not part of the device. See host system programming.
A simple utility using National Instruments NI-FBUS is available from
Flowserve for retrieving a signature file.
The retrieved file is stored in a text format that can be imported into
other programs for plotting and analysis. Contact Flowserve for more
details.
7.17 Glossary
A/D
Also called ADC. Analog-to-digital converter. An A/D converts an
analog signal into an integer count. This integer count is then used by
the microcontroller to process sensor information such as position,
pressure, and temperature.
D/A
Also called DAC. Digital-to-analog converter. A D/A converts an
integer count into an analog output signal. The D/A is used to take a
number from the microcontroller and command an external device such
as a pressure modulator.
DTM (Device Type Manager)
Provides a GUI nterface for the user to
easily view and analyze the status of the valve and positioner.
EEPROM (Electrically Erasable Programmable Read Only
Memory)
A device that retains data even when power is lost.
Electrically erasable means that data can be changed. EEPROM have
a limited number of times data can be rewritten (typically 100,000 to
1,000,000 writes).
Micro-controller
In addition to an integral CPU (microprocessor), the
micro-controller has built in memory and I/O functions such as A/D and
D/A.
