Emerson Fisher 785C Configuration guide

www.Fisher.com

Safety Manual for Fisher™785C Actuators

Purpose

This safety manual provides information necessary to design, install, verify, and maintain a Safety Instrumented

Function (SIF) utilizing the Fisher 785C actuator.

WARNING

This instruction manual supplement is not intended to be used as a stand-alone document. It must be used in conjunction

with the following manual:

Fisher 785C Actuator Instruction Manual (D104483X012)

Failure to use this instruction manual supplement in conjunction with the above referenced manual could result in personal

injury or property damage. If you have any questions regarding these instructions or need assistance in obtaining any of

these documents, contact your Emerson sales office.

Introduction

This manual provides necessary requirements for meeting the IEC 61508 or IEC 61511 functional safety standards.

Figure 1. Fisher 785C Actuator

785C Double-Acting Springless Actuator

785C Actuator

April 2019

Instruction Manual Supplement

D104484X012

Instruction Manual Supplement

D103398X012

785C Actuator

April 2019

Terms and Abbreviations

Safety: Freedom from unacceptable risk of harm.

Functional Safety: The ability of a system to carry out the actions necessary to achieve or to maintain a defined safe

state for the equipment / machinery / plant / apparatus under control of the system.

Basic Safety: The equipment must be designed and manufactured such that it protects against risk of injury to persons

by electrical shock and other hazards and against resulting fire and explosion. The protection must be effective under

all conditions of the nominal operation and under single fault condition.

Safety Assessment: The investigation to arrive at a judgment  based on the facts  of the safety achieved by

safetyrelated systems.

FailSafe State:

D State where valve actuator is deenergized and spring is extended. (785C single-acting spring return constructions).

D State where valve actuator is driven to or held in a predefined position by the control medium. (785C double-acting

springless constructions).

Fail Safe: Failure that causes the valve to go to the defined failsafe state without a demand from the process.

Fail Dangerous: Failure that does not respond to a demand from the process (i.e. being unable to go to the defined

failsafe state).

Fail Dangerous Undetected: Failure that is dangerous and that is not being diagnosed by automatic stroke testing.

Fail Dangerous Detected: Failure that is dangerous but is detected by automatic stroke testing.

Fail Annunciation Undetected: Failure that does not cause a false trip or prevent the safety function but does cause

loss of an automatic diagnostic and is not detected by another diagnostic.

Fail Annunciation Detected: Failure that does not cause a false trip or prevent the safety function but does cause loss of

an automatic diagnostic or false diagnostic indication.

Fail No Effect: Failure of a component that is part of the safety function but that has no effect on the safety function.

Low demand mode: Mode, where the frequency of demands for operation made on a safetyrelated system is no

greater than twice the proof test frequency.

Acronyms

FMEDA: Failure Modes, Effects and Diagnostic Analysis

HFT: Hardware Fault Tolerance

MOC: Management of Change. These are specific procedures often done when performing any work activities in

compliance with government regulatory authorities.

PFDAVG:Average Probability of Failure on Demand

SFF: Safe Failure Fraction, the fraction of the overall failure rate of a device that results in either a safe fault or a

diagnosed unsafe fault.

SIF: Safety Instrumented Function, a set of equipment intended to reduce the risk due to a specific hazard (a safety

loop).

Instruction Manual Supplement

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April 2019

SIL: Safety Integrity Level, discrete level (one out of a possible four) for specifying the safety integrity requirements of

the safety functions to be allocated to the E/E/PE safetyrelated systems where Safety Integrity Level 4 has the highest

level of safety integrity and Safety Integrity Level 1 has the lowest.

SIS: Safety Instrumented System – Implementation of one or more Safety Instrumented Functions. A SIS is composed

of any combination of sensor(s), logic solver(s), and final element(s).

Related Literature

Hardware Documents:

Bulletin:

61.2:785C, Fisher 785C Piston Actuator: D104412X012

Instruction Manual:

Fisher 785C Piston Actuator: D104483X012

Guidelines/References:

D Safety Integrity Level Selection – Systematic Methods Including Layer of Protection Analysis, ISBN 1556177771,

ISA

D Control System Safety Evaluation and Reliability, 2nd Edition, ISBN 1556176388, ISA

D Safety Instrumented Systems Verification, Practical Probabilistic Calculations, ISBN 1556179099, ISA

Reference Standards

Functional Safety

D IEC 61508: 2010 Functional safety of electrical/electronic/ programmable electronic safetyrelated systems

D ANSI/ISA 84.00.012004 (IEC 61511 Mod.) Functional Safety – Safety Instrumented Systems for the Process Industry

Sector

Product Description

The 785C Series pneumatic actuators are medium to large spring-return single acting or double-acting springless

piston actuators that provide accurate, high thrust output for short to long travel applications. The 785C actuators can

be installed on sliding-stem valves for throttling control or on-off applications.

The single-acting actuator constructions feature an internal bias spring that forces the actuator piston rod to extend or

retract upon a loss of supply pressure, thereby ensuring a fail-closed or fail-open mode of operation. This effectively

eliminates the need for a trip valve and volume tank in most constructions.

An optional manual override (top mounted handwheel or side mounted handpump) is capable of extending or

retracting the actuator manually and can be engaged at any position from full open to full close. The top-mounted

handwheel utilizes an engagement lever that couples the handwheel and piston rod. The handpump has a hydraulic

cylinder attached to the piston rod. This enables the handpump to operate the actuator manually, unless the

handpump is set to bypass position.

Instruction Manual Supplement

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785C Actuator

April 2019

Designing a SIF Using a Fisher 785C Actuator

Safety Function

The double-acting springless 785C actuator constructions will maintain functionality so the actuator can be moved

into the application dependent safe state by means of the control medium. When the spring-return 785C actuator is

de-energized, the actuator and valve shall move to its fail-safe position. Depending on which configuration is specified

fail-closed or fail-open, the actuator will move the valve control element to close off the flow path through the valve

body or open the flow path through the valve body.

The 785C actuator is intended to be part of a final element subsystem as defined per IEC 61508 and the achieved SIL

level of the designed function must be verified by the designer.

Environmental Limits

The designer of an SIF must check that the product is rated for use within the expected environmental limits. Refer to

the Fisher 785C Actuator Product Bulletin (D104412X012) for environmental limits.

Application limits

The 785C series actuator materials of construction are specified in the product bulletin. A range of materials for

certain parts are available for various applications. The serial card will indicate what the materials of construction are

for a specific actuator. It is especially important that the designer check for material compatibility considering onsite

chemical contaminants and air supply conditions. If the 785C series actuator is used outside of the application limits or

with incompatible materials, the reliability data provided becomes invalid.

Diagnostic Response Time

A 785C series actuator does not perform any automatic diagnostic functions by itself and therefore it has no

diagnostic response time of its own. However, automatic diagnostics of the final control subsystem may be performed

such as Partial Valve Stroke Testing (PVST). This typically will exercise the actuator and valve over a small percentage of

its normal travel without adversely affecting the flow through the valve. If any failures of this PVST are automatically

detected and annunciated, the diagnostic response time will be the PVST interval time. The PVST must be performed

10 times more often than an expected demand in order for credit to be given for this test.

Design Verification

The achieved SIL of an entire SIF design must be verified by the designer via a calculation of PFDAVG considering

architecture, proof test interval, proof test effectiveness, any automatic diagnostics, average repair time and the

specific failure rates of all products included in the SIF. Each subsystem must be checked to assure compliance with

minimum HFT requirements.

When using a 785C series actuator in a redundant configuration, a common cause factor of at least 10% should be

included in the Safety Integrity calculations. This value is dependent on the level of common cause training and

maintenance in use at the end user's facility.

The failure rate data listed in the SIL certificate is only valid for the useful lifetime of a 785C series actuator. The failure

rates will increase after this time period. Reliability calculations based on the data listed in the SIL certificate for

mission times beyond the useful lifetime may yield results that are too optimistic, i.e. the calculated Safety Integrity

Level will not be achieved.

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SIL Capability

Systematic Integrity

The product has met manufacturer design process requirements of SIL 3. These are intended to achieve sufficient

integrity against systematic errors of design by the manufacturer. A SIF designed with this product must not be used at

a SIL level higher than stated without “prior use” justification by the end user or diverse technology redundancy in the

design.

Random Integrity

The Fisher 785C series actuator is classified as a Type A device according to IEC 61508, having a hardware fault

tolerance of 0. The complete final element subsystem, with a 785C series actuator and sliding stem valve as the final

control element, will need to be evaluated to determine the Safe Failure Fraction of the subsystem. If the SFF for the

entire final element subsystem is between 60% and 90%, a design can meet SIL 2 @ HFT=0.

Safety Parameters

For detailed failure rate information refer to the SIL certificate for the Fisher 785C Spring Return actuators or the SIL

certificate for the Fisher 785C Double Acting actuators.

Connection of the Fisher 785 Actuator to the SIS Logic-solver

The final element subsystem (consisting of a positioner, 785C series actuator, and a sliding-stem valve) is connected

to the safety rated logic solver which is actively performing the Safety Function as well as any automatic diagnostics

designed to diagnose potentially dangerous failures within the 785C series actuator, valve and any other final element

components (i.e. Partial Valve Stroke Test).

General Requirements

The system's response time shall be less than process safety time. The final control element subsystem needs to be

sized properly to assure that the response time is less than the required process safety time. The 785C series actuator

will move the valve to its safe state in less than the required SIF's safety time under the specified conditions.

All SIS components including the 785C series actuator must be operational before process startup.

The user shall verify that the 785C series actuator is suitable for use in safety applications.

Personnel performing maintenance and testing on the 785C series actuator and valve shall be competent to do so.

Results from the proof tests shall be recorded and reviewed periodically.

The useful life of the 785C series actuator is expected to be approximately 25 years with proper maintenance but

depends on operating conditions and construction materials.

Installation and Commissioning

Installation

WARNING

To ensure safe and proper functioning of equipment, users of this document must carefully read all instructions, warnings,

and cautions in each applicable instruction manual.

Instruction Manual Supplement

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785C Actuator

April 2019

The Fisher 785C series actuator must be installed per standard practices outlined in the instruction manual.

The environment must be checked to verify that environmental conditions do not exceed the ratings.

The 785C actuator must be accessible for physical inspection.

Physical Location and Placement

The 785C series actuator shall be accessible with sufficient room for the valve, actuator, pneumatic connections, and

any other components of the final control element. Provisions shall be made to allow for manual proof testing.

Pneumatic piping to the actuator shall be kept as short and straight as possible to minimize the airflow restrictions and

potential clogging. Long or kinked pneumatic tubes may also increase the valve closure time.

The 785C series actuator shall be mounted in a low vibration environment. If excessive vibration can be expected

special precautions shall be taken to ensure the integrity of pneumatic connectors or the vibration should be reduced

using appropriate damping mounts.

Pneumatic Connections

Recommended piping for the inlet and outlet pneumatic connections to the 785C series actuator is stainless steel

tubing. The length of tubing between the 785C series actuator and the control device, such as a solenoid valve, shall

be kept as short as possible and free of kinks.

The process air pressure shall meet the requirements set forth in the installation manual.

The process air capacity shall be sufficient to move the valve within the required time.

The actuator is shipped with two plastic NPT plugs in the ports to keep the cylinder free of debris. Verify these have

been replaced with appropriate pressure retaining components before pressurizing.

Note

The plastic NPT plugs may be removed by the Fisher factory during manufacturing for mounting of a valve controller, positioner, or

other final element component.

Instruction Manual Supplement

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785C Actuator

April 2019

Operation and Maintenance

Suggested Proof Test

The objective of proof testing is to detect failures within a 785C series actuator that are not detected by any automatic

diagnostics of the system. Of main concern are undetected failures that prevent the Safety Instrumented Function

from performing its intended function.

The frequency of proof testing, or the proof test interval, is to be determined in reliability calculations for the Safety

Instrumented Functions for which a 785C series actuator is applied. The proof tests must be performed more

frequently than or as frequently as specified in the calculation in order to maintain the required Safety Integrity of the

Safety Instrumented Function.

The proof test shown in table 1 is recommended. The results of the proof test should be recorded and any failures that

are detected and that compromise functional safety should be reported to Emerson Automation Solutions. The

suggested proof test consists of a full stroke of the 785C series actuator.

The person(s) performing the proof test of a 785C series actuator should be trained in SIS operations, including bypass

procedures, valve maintenance and company Management of Change procedures. No special tools are required.

Table 1. Recommended Full Stroke Proof Test

Step Action

1Bypass the safety function and take appropriate action to avoid a false trip.

2Interrupt or change the signal/supply to the 785C actuator to force the actuator and valve to perform a full stroke

to the FailSafe state and confirm that the Safe State was achieved and within the correct time.

3Restore the supply/signal to the 785C actuator and confirm that the normal operating state was achieved.

4Inspect the 785C actuator and the other final control element components for any leaks, visible damage or contamination.

5Record the test results and any failures in your company's SIF inspection database.

6Remove the bypass and restore normal operation.

Repair and replacement

Repair and replacement procedures in the instruction manuals must be followed.

Manufacturer Notification

Any failures that are detected and that compromise functional safety should be reported to Emerson. Please contact

your Emerson sales office.

Instruction Manual Supplement

D103398X012

785C Actuator

April 2019

Appendix A

Sample Startup Checklist

This appendix provides a sample Startup Checklist for a 785C actuator. A Startup Checklist will provide guidance

during the final control elements employment.

Start-Up Checklist

The following checklist may be used as a guide to employ the 785C actuator in a safety critical SIF compliant to

IEC61508.

# Activity Result Verified

By Date

Design

Target Safety Integrity Level and PFDAVG determined

Correct valve mode chosen (Failclosed, Failopen)

Design decision documented

Pneumatic compatibility and suitability verified

SIS logic solver requirements for valve tests defined and documented

Routing of pneumatic connections determined

SIS logic solver requirements for partial stroke tests defined and

documented

Design formally reviewed and suitability formally assessed

Implementation

Physical location appropriate

Pneumatic connections appropriate and according to applicable codes

SIS logic solver valve actuation test implemented

Maintenance instructions for proof test released

Verification and test plan released

Implementation formally reviewed and suitability formally assessed

Verification and Testing

Electrical connections verified and tested

Pneumatic connection verified and tested

SIS logic solver valve actuation test verified

Safety loop function verified

Safety loop timing measured

Bypass function tested

Verification and test results formally reviewed and suitability formally

assessed

Maintenance

Tubing blockage / partial blockage tested

Safety loop function tested

Emerson Automation Solutions

Marshalltown, Iowa 50158 USA

Sorocaba, 18087 Brazil

Cernay, 68700 France

Dubai, United Arab Emirates

Singapore 128461 Singapore

www.Fisher.com

The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure their accuracy, they are not

to be construed as warranties or guarantees, express or implied, regarding the products or services described herein or their use or applicability. All sales are

governed by our terms and conditions, which are available upon request. We reserve the right to modify or improve the designs or specifications of such

products at any time without notice.

Fisher is a mark owned by one of the companies in the Emerson Automation Solutions business unit of Emerson Electric Co. Emerson Automation Solutions,

Emerson, and the Emerson logo are trademarks and service marks of Emerson Electric Co. All other marks are the property of their respective owners.

Neither Emerson, Emerson Automation Solutions, nor any of their affiliated entities assumes responsibility for the selection, use or maintenance

of any product. Responsibility for proper selection, use, and maintenance of any product remains solely with the purchaser and end user.

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