Safety Considerations Guide for Triconex General ... - ICEWeb
Safety Considerations Guide for Triconex General ... - ICEWeb
Safety Considerations Guide for Triconex General ... - ICEWeb
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74 Appendix B HART Communication<br />
2008-04-01<br />
1. Scope<br />
The scope of this paper is to review the use of the HART communication as a non-safety<br />
related communication protocol within safety related applications using a <strong>Safety</strong> Instrumented<br />
System (SIS).<br />
2. Standards<br />
Functional <strong>Safety</strong><br />
[1] IEC 61508:2000, parts 1 - 7<br />
Functional safety of electrical/electronic/programmable electronic safety related systems<br />
[2] IEC 61511:2004, parts 1 - 3<br />
Functional safety - <strong>Safety</strong> instrumented systems <strong>for</strong> the process industry sector<br />
3. Analysis<br />
3.1 <strong>General</strong> analysis<br />
The HART (Highway Addressable Remote Transducer) communication protocol is a widely<br />
accepted standard used <strong>for</strong> communication between intelligent field instruments and host<br />
systems.<br />
HART is a master-slave field communication protocol, which use a phase-continuous<br />
Frequency Shift Keying (FSK) to extend analog signaling, whereas a high-frequency current is<br />
superimposed on a low-frequency analog current typically 4-20 mA.<br />
The benefit of HART that it can be used in parallel to the analog 4-20 mA field devices using the<br />
same wiring in which a bi-directional communication to several HART capable field devices is<br />
supported.<br />
Devices which use HART as a communication protocol can be divided into two groups:<br />
HART Master Devices<br />
The master devices are typically multiplexer devices with a HART modem which are connected<br />
directly through the field wiring of a host system (input/output system) typically a programmable<br />
logic controller. They are in general used to configure slave devices and provide additional<br />
diagnostics to a host system.<br />
HART Slave devices<br />
The slave devices are in general HART capable intelligent field devices using an analog<br />
4-20 mA current <strong>for</strong> process values.<br />
3.2 <strong>Safety</strong> analysis<br />
The HART communication protocol was developed to be used within standard process control<br />
systems <strong>for</strong> device configuration and diagnostics. The development itself was not per<strong>for</strong>med in<br />
accordance to the IEC 61508 [1] and it was not approved as a safety related communication<br />
protocol.<br />
Considering the development of the HART communication protocol the following assumptions<br />
can be made according to the safety impact and interference of HART capable devices, which<br />
are intended to be used together with a safety related system.<br />
HART_in_<strong>Safety</strong>_Related_Applications_pdf.doc<br />
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<strong>Safety</strong> <strong>Considerations</strong> <strong>Guide</strong> <strong>for</strong> <strong>Triconex</strong> <strong>General</strong> Purpose v2 Systems