Flowserve 3400MD Digital Positioner - Manual (Page 24)

Logix 3400MD Digital Positioner FCD LGENIM3404-08-AQ –5/15
24
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 values 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 parameters SIG_DATA1 – SIG_DATA26 can be populated with
the full signature data by writing a non-zero value to the SIG_INDEX
parameter.
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 interface 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.
Microprocessor Semiconductor device capable of performing
calculations, data transfer, and logic decisions. Also referred to as
CPU (Central Processing Unit).
Protocol A set of rules governing how communications messages
are sent and received.
Resolution Resolution is a number which indicates the smallest
measurement which can be made. You will often see analog-to-digital
(A/D) converters referred to as a 10-bit A/D or a 12-bit A/D. 10-bit
and 12-bit are terms which indicate the total number of integer counts
which can be used to measure a sensor or other input. To determine
the total integer count, raise 2 to the power of the number of bits.
Example: 12-bit A/D
Total integer number = 2
Number of Bits = 212= 4096
Resolution is the measurement range divided by the maximum
integer number. Example: A valve has a 2-inch stroke and a 12-bit
A/D is used to measure position. Resolution = Stroke/(Maximum
Integer for 12-bit) = 2 inch/4096 = 0.000488 inches Sampling Taking
readings at periodic time intervals.
Serial Channel Channel that carries serial transmission. Serial
transmission is a method of sending information from one device to
another. One bit is sent after another in a single stream.