55
Logix
®
520MD+ and 510+ Digital Positioners FCD LGENIM0105-15-AQ – 05/16
flowserve.com
17 REQUIREMENTS FOR SAFETY
INTEGRITY
This section provides information and additional user responsibilities in
order to meet up to Safety Integrity Level 3 (SIL 3) per IEC 61508.
The safety function of the positioner is to go to the fail-safe state (vent
air from the actuator) given a low power condition to the 4 to 20 mA
input terminal.
17.1 Fail Safe State
The fail safe state for a positioner with a three-way (Single-Acting), Pop-
pet Style Relay is when the relay valve is at less than 5% of full stroke
such that output port B (Y1) is venting.
The fail safe state for a positioner with a three-way (Single-Acting),
Spool Style Relay is when the relay valve is at less than 5% of full stroke
such that output port A (Labeled Y1) is venting.
The fail safe state for a positioner with a four-way (Double-Acting),
Spool Style Relay is when the relay valve is at less than 5% of full stroke
such that output port A (labeled Y1) is venting and port A (labeled Y2) is
open to supply pressure.
NOTE:
The fail safe states above represent the fail safe state of the
positioner. The valve fail safe state may be different depending on
spring configuration and tubing. Ensure the valve fail-safe state is
appropriate for your application.
17.2 Safety Function
The Logix 520MD+ positioner moves to fail-safe state upon the removal
of analog input power (less than 3.6 mA)
NOTE:
If using the V to I card, less than 10 Volts at the V to I card
terminals will produce a current less than 3.6 mA.
17.3 Fail Safe State Response Time
Test to find the final valve assembly response time to ensure it meets
application-specific requirements. Response times will vary widely with
actuator size, the use of boosters, stroke length, starting position, fail-
safe direction, tubing size, supply pressure, and temperature. The air
flow capacity also affects the response time. See section 2.2 Pneumatic
Output for air flow capacity.
A typical* response time for the spool relay to move to a fail-safe state
due to a sudden command change was found to be 0.06 seconds. (The
response time was 0.50 s at -40C and .35 s at 85C.)
The time for the valve to move to from 50% to 0% under the same
conditions was found to be 0.22 s. Friction in this case was 49.5 lbs
(220 N).
*Tests were with a 25 inch double acting Mark 1 actuator, 0.75 inch
(19 mm) stroke, ambient temperature 74°F (23.3 °C), 60 PSI (4.1
bar) supply, quarter inch tubing, starting at 50% open, moving to fully
closed. Friction was calculated with a bi-directional ramp test at a rate of
10 seconds/100%.
A typical** response time for the poppet relay to move to a fail-safe
state due to a sudden command change was found to be 0.10 s at 22 C,
0.23 s at -40 C and .13 s at 85 C.
**Tests were with 60 PSI (4.1 bar) supply pressure.
NOTE:
During the stroke calibration (Quick-Cal), valve stroke times
are measured and recorded in the positioner. To view them, see
tuning parameters on the positioner menu or in the DTM.
17.4 Positioner Model Selection and Specification
Any Logix 520MD+ positioner can be used for up to SIL 3 applications
as stated above.
17.5 Installation
Ensure installation of the positioner is properly performed according
to this manual. Ensure tubing is configured to the actuator so that the
fail-safe state of the positioner matches the desired fail-safe state of the
valve.
17.6 Required Configuration Settings
The following user settable options must be properly configured for the
individual application in order to provide the designed safety integrity
for that application.
• Calibrate the analog input (command). The fail safe state of the valve
must correspond to the analog input command at less than 3.6 mA.
• It is recommended to lock the local interface to prevent unintended
adjustments of the settings by an unauthorized user.
17.7 Maximum Achievable SIL
The Flowserve 520MD+ Valve Positioner covered by this safety manual
is suitable for use in low demand mode of operation Safety Integrity
Functions (SIF) up to SIL 2 in simplex (1oo1) and SIL 3 in redundant
(1oo2) configurations. The achieved SIL for a particular SIF needs to
be verified by PFDAVG calculation for the entire SIF including the failure
rates of the associated sensors and valves that are also part of the SIF.
For details, contact your Flowserve representative for Failure Mode,
Effects, and Diagnostics Analysis (FMEDA) report number 520+ is FLO
11-02-062 R001 for Logix 520MD+.
17.8 Reliability data
For reliability data, a detailed Failure Mode, Effects, and Diagnostics
Analysis (FMEDA) report has been prepared and is available from Flow-
serve with all failure rates and failure modes for use in SIL verification.
See FMEDA report number FLO 11-02-062 R001 for Logix 520MD+.
NOTE:
The failure rates of the associated sensors, logic solver,
valves and actuators need to be accounted for in the Safety
Instrumented Function (SIF) level PFDAVG calculation.
