Masoneilan SVI II ESD, Руководство по установке и обслуживанию

Страница: 21 / 220

Masoneilan SVI II ESD Installation and Maintenance Manual =
|
21
© 2017 Baker Hughes, a GE company, LLC. All rights reserved.
Designing an SIF Using an SVI II ESD
The following must be taken into consideration when designing a SIF (Safety Instrumented
Function) using the SVI II ESD:
Safety Function
Environmental Limits
Design Verification
SIL Capability
Connecting the SVI II ESD to the SIS Logic-Solver
General Requirements
Safety Function
When de-energized, the SVI II ESD moves to its fail-safe position. For a single-acting PST
controller the safe state is when the port
Actuator 1 is exhausted to a pressure less than 1
PSIG (0.069 bar, 6.9 kPa). The valve actuation must automatically move the valve to the safe
state when the digital valve controller falls in safe state.
The SVI II ESD is intended to be part of final element subsystem, as per IEC 61508, and the
achieved SIL level of the function must be verified by the function designer.
Environmental Limits
The designer of a SIF must check that the product is rated for use within the environmental
limits as stated in Table 14 on page 161.
Application Limits
Listed below are the application limits for the SVI II ESD installed in a SIF:
The application of the SVI II ESD is limited for SIF where the safe state is the
de-energized state (shutdown) of the valve. The PST Controller can be operated with
either one of two control signals: 4 - 20 mA or 0 - 24 VDC.
With a 4 - 20 mA control signal, normal operation is with a 20 mA current loop signal to
the PST controller. A shutdown command is issued by bringing the current to 5.6 mA or
lower.
With a 0 - 24 VDC control signal, normal operation is with a 24 VDC signal applied to
the PST controller. A shutdown command is issued by opening the loop or bringing the
control signal to 3 VDC or lower.