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1. Figure 2 2 PFD distribution Safety Manual Operating Instructions 06 2012 A5E03433511 05 General description of functional safety 2 2 Safety integrity level The following table shows the achievable Safety Integrity Level SIL for the entire safety instrumented system for type B subsystems depending on the proportion of safe failures SFF and the hardware fault tolerance HFT Type B subsystems include sensors with positioners actuators with complex components e g microprocessors see also IEC 61508 Section 2 Table 2 2 Achievable Safety Integrity Level type B subsystems SFF HFT 0 1 0 2 1 lt 60 Not allowed SIL 1 SIL 2 60 90 SIL 1 SIL 2 SIL 3 90 99 SIL 2 SIL 3 SIL 4 gt 99 SIL 3 SIL 4 SIL 4 As per IEC 61511 1 Section 11 4 4 Operational reliability According to IEC 61511 1 Section 11 4 4 the hardware fault tolerance HFT can be reduced by one values in brackets for transmitters and final controlling elements with complex components if the following conditions are applicable to the device e The device is proven in operation e The user can configure only the process related parameters e g control range signal direction in case of a fault limiting values etc e The configuration level of the firmware is blocked against unauthorized operation e The function requires SIL of less than 4 The device fullfils these conditions2. 2 2 Safety integrity level 2 2 Definitions Description 10 Safety integrity level SIL Safety Integrity Level The international standard IEC 61508 defines four discrete Safety Integrity Levels SIL from SIL 1 to SIL 4 Each level corresponds to the probability range for the failure of a safety function The higher the SIL of the safety instrumented system the higher probability that the required safety function will work The achievable SIL is determined by the following safety characteristics e Average probability of dangerous failure of a safety function in case of demand PFDave e Hardware fault tolerance HFT e Safe failure fraction SFF The following table shows the dependency of the SIL on the average probability of dangerous failures of a safety function of the entire safety instrumented system PFDave The table deals with Low demand mode i e the safety function is required a maximum of once per year on average Table 2 1 Safety Integrity Level SIL Interval 4 10 lt PFDave lt 10 3 104 lt PFDave lt 103 2 10 3 lt PFDave lt 10 2 1 10 2 lt PFDave lt 10 1 The average probability of dangerous failures of the entire safety instrumented system PFDave is normally split between the three sub systems in the following figure Sensor Control system Final controlling or logic unit element e g Pp veg ve 9 gas analyzer PLC valve
3. Safety Manual Operating Instructions 06 2012 A5E03433511 05 11 General description of functional safety 2 2 Safety integrity level Safety Manual 12 Operating Instructions 06 2012 A5E03433511 05 Device specific Safety Instructions 3 3 1 Applications The SITRANS SL is suitable for use in a safety instrumented function of Safety Integrity Level SIL 1 low demand mode within a 1001 architecture The safety related characteristics listed in the respective SIL Declaration of Conformity may be used in the relevant calculations required for IEC 61508 61511 safety instrumented system compliance 3 2 Safety function The safety function at SITRANS SL refers to the measurement of gas concentrations The concentration is converted into an analog measured value and supplied over a 4 20 mA NAMUR analog output Fault tolerance allowances must be made because the measured value transferred to the automation system by SITRANS SL can deviate from the physical value The total tolerance safety function is calculated as follows Total tolerance safety function application specific measuring error at operating conditions 5 safety accuracy of full scale value The application specific measuring error at operating conditions is calculated from the application specific measuring error under reference conditions and the measuring error caused by the influencing variables which depend on the operating conditions T
4. Output configuration Select analog output 0 for gas component Path length Enter correct path length Enter the following parameter via configuration tool LDSComm Function Action Alarm configuration Select System I O Analog Outputs Analog Output 0 tab Set alarm action for all faults and warnings to 3 mA Performing this configuration requires LDSComm user level service References e SITRANS SL Operating instructions 1 e LDSComm Operating manual Article no A5E02350886 Protection against configuration changes After configuration the SITRANS SL LUI password shall be changed using the LDSComm software to protect the device against unintentional and unauthorized changes operation Within LDSComm the LUI password can be found under the Device Service tab This entry requires LDSComm user level service Checking the safety function after installation Following installation and commissioning of the SITRANS SL a safety function test has to be carried out as described in section Maintenance and checks Page 18 Safety Manual 16 Operating Instructions 06 2012 A5E03433511 05 Device specitic Safety Instructions 3 5 Behavior in case of faults Faults The procedure in case of faults is described in the Operating Instructions of the device Repairs Defective devices should be sent to the Repair Department stating details and cause of any fault When ordering replacement devices also the ser
5. the applied current Select analog input test for Analog Pressure using LUI Connect a calibrated current source e g a loop calibrator to the analog input 1 for pressure Note the current measuring instrument used for this test shall provide an accuracy of 0 1 or better 7 Apply at least the following currents in succession 4 0 mA 20 0 mA and a current value within this interval to the analog input The indicated measured values mA shall not deviate more than 0 5 from the applied current Restore the loop to full operation Remove the bypass from the safety PLC and restore to normal operation Table 3 4 Proof test part 4 Step Action 1 Bypass the safety PLC or take another appropriate action to avoid a false trip 2 Unlock the LUI using the service password Security menu 3 Select analog output test analog output 0 using LUI 4 Connect a calibrated current measuring instrument with loop powering capability e g a loop calibrator to the analog output 0 Note the current measuring instrument used for this test shall provide an accuracy of 0 1 or better 5 Set at least the following currents in succession 4 0 mA 20 0 mA and a current value within this interval to the analog output The measured current shall not deviate more than 0 5 from the set current Select analog output test analog output 1 using LUI 7 Connect a calibrated current measuring instrument
6. to a specific hazardous event SIL Safety Integrity Level The international standard IEC 61508 defines four discrete Safety Integrity Levels SIL 1 to SIL 4 Each level corresponds to a probability range for failures of a safety function The higher the Safety Integrity Level of the safety instrumented system the lower the probability that it will not execute the required safety functions TI Test Interval Testing interval of the protective function XooY X out of Y voting Classification and description of the safety instrumented system in terms of redundancy and the selection procedures used in which Y specifies how often a safety function is executed redundancy and X determines how many channels have to work correctly Example Pressure measurement in a 1002 architecture A safety instrumented system decides that a specified pressure limit has been exceeded if one out of two pressure sensors reaches this limit In a 1001 architecture there is only one pressure sensor 22 Safety Manual Operating Instructions 06 2012 A5E03433511 05 Glossary Dangerous failure Failure with the potential to bring the safety instrumented system into a dangerous or non functional status Fail safe The capability of a control to maintain the safe state of the controlled device e g machine process or to bring the device to a safe state even when faults failures occur Failure Fault Failur
7. valve Converter that converts mechanical or other non electrical variables into electrical signals Safety Manual Operating Instructions 06 2012 A5E03433511 05 Siemens AG Subject to changes without prior notice Industry Sector ID A5E03433511 Sensors and Communication 76181 KARLSRUHE GERMANY Siemens AG 2011 2012 www siemens com processanalytics
8. with loop powering capability e g a loop calibrator to the analog output 1 Note the current measuring instrument used for this test shall provide an accuracy of 0 1 or better 8 Set at least the following currents in succession 4 0 mA 20 0 mA and a current value within this interval to the analog output The measured current shall not deviate more than 0 5 from the set current Restore the loop to full operation 10 Remove the bypass from the safety PLC and restore to normal operation Safety Manual Operating Instructions 06 2012 A5E03433511 05 19 Device specific Safety Instructions 3 7 See also 20 Safety characteristics The safety characteristics necessary for use of the system are listed in the SIL declaration of conformity These values apply under the following conditions The SITRANS SL is only used in safety related systems with a low demand mode for the safety function When external sensors for process temperature and process pressure are used they have to be considered as part of the Safety related system Purging of sensors must be considered as part of the Safety related system The safety related parameters settings see chapter Settings Page 16 have been entered by local operation and checked before starting safety instrumented operation The SITRANS SL is blocked against unintentional and unauthorized changes operation All used materials are compatible with process co
9. 1 1 05 21 List of abbreviations Abbreviation O2 Full term Oxygen molecular formula Meaning Chemical element with atomic number 8 and represented by the symbol O Its name derives from the Greek roots acid literally sharp referring to the sour taste of acids and yev producer literally begetter because at the time of naming it was mistakenly thought that all acids required oxygen in their composition At standard temperature and pressure two atoms of the element bind to form dioxygen a colorless odorless tasteless diatomic gas with the formula O In case of SITRANS SL A measuring component PFD Probability of Failure on Demand Probability of dangerous failures of a safety function on demand PFDavc Probability of Failure on Demand AVERAGE Average probability of dangerous failures of a safety function on demand PLC Programmable Logic Controller A digital computer used for automation of industrial processes such as machinery control in factories SFF Safe Failure Fraction Proportion of safe failures Proportion of failures without the potential to bring the safety instrumented system into a dangerous or impermissible functional status SIF Safety Instrumented Function Function to be implemented by a safety related system or an external risk reduction facility which is intended to achieve or maintain a safe state for the process with respect
10. SITRANS SL In situ Laser Gas Analyzer Safety Manual Supplement to Operating Instructions Continuous Gas Analysis SIEMENS SIEMENS Continuous Gas Analysis In situ Laser Gas Analyzers Safety Manual Operating Instructions Supplement to SITRANS SL Operating Instructions 06 2012 A5E0343351 1 05 Introduction General description of functional safety Device specific Safety Instructions List of abbreviations Bb O IN Legal information Warning notice system This manual contains notices you have to observe in order to ensure your personal safety as well as to prevent damage to property The notices referring to your personal safety are highlighted in the manual by a safety alert symbol notices referring only to property damage have no safety alert symbol These notices shown below are graded according to the degree of danger indicates that death or severe personal injury will result if proper precautions are not taken WARNING indicates that death or severe personal injury may result if proper precautions are not taken CAUTION with a safety alert symbol indicates that minor personal injury can result if proper precautions are not taken CAUTION without a safety alert symbol indicates that property damage can result if proper precautions are not taken NOTICE indicates that an unintended result or situation can occur if the relevant information is no
11. ation This document deals with the SITRANS SL in situ laser gas analyzer exclusively as part of a safety function This document is valid only in conjunction with one of the following documents No Designation Order no 1 SITRANS SL Operating Instructions A5E01132948 English A5E01132949 German A5E01132951 French A5E01132952 Italian A5E01132953 Spanish Safety Manual Operating Instructions 06 2012 A5E03433511 05 Introduction 1 5 History 1 5 History The following table shows the released versions and the changes in the documentation compared to each preceding edition Edition Remark 01 First edition 02 2011 02 Introduction of CO as new measuring component 06 2011 03 Update of Certificate of Conformity 08 2011 04 Recalculation of safety function tolerance 10 2011 05 Proven in use for SITRANS SL O2 06 2012 1 6 Further information Information The contents of these instructions shall not become part of or modify any prior or existing agreement commitment or legal relationship All obligations on the part of Siemens AG are contained in the respective sales contract which also contains the complete and solely applicable warranty conditions Any statements contained herein do not create new warranties or modify the existing warranty The content reflects the technical status at the time of printing We reserve the right for technical changes in the course of fu
12. cks Page 18 If the device detects a failure by diagnosis the system must be brought to a safe state and the device shall be repaired within the Mean Time To Restoration MTTR The base of this PFD calculation is a MTTR of 72 hours Certificate of Conformity SITRANS SL Functional Safety http support automation siemens com WW view en 10806991 134200 Safety Manual Operating Instructions 06 2012 A5E0343351 1 05 Device specitic Safety Instructions 3 3 Application restrictions Installation and configuration of the SITRANS SL must be completed following the instructions detailed in the Operating Instructions of the device 1 All application limitations and restrictions described in that manual must be observed 3 3 1 Temperature and pressure Safety recommendations for process temperature and process pressure Process temperature and process pressure measurements have an influence on the concentration measurement by SITRANS SL and thus must be considered upon installation of the analyzer The measurement of temperature and pressure must reflect the process conditions at the measurement point Otherwise the error in concentration measurement increases If the process conditions for temperature and pressure can not assumed to be constant external sensors for temperature and pressure are highly recommended SITRANS SL provides two analog input channels 4 to 20 mA for external temperature and pressure signals Any exter
13. e A resource is no longer capable of executing a required function Fault Undesired state of a resource indicated by the incapability of executing a required function Fault tolerance Fault tolerance n means that a device can execute the intended task even when n faults exist The device fails to execute the intended function in case of n 1 faults Final controlling element Converter that converts electrical signals into mechanical or other non electrical variables Low Demand Mode The frequency of demands for operation made on a safety related system is not more than one per year and not more than twice the proof test frequency Risk The combination of the probability of a damage occurring and its magnitude Safety Manual Operating Instructions 06 2012 A5E03433511 05 23 Glossary Safety function Defined function executed by a safety instrumented system with the objective of achieving or maintaining a safe system status which takes into account a defined occurrence of dangerous failures Example Monitoring of user defined limit values Safety instrumented system Sensor 24 A safety instrumented system excludes the safety functions that are required to achieve or maintain a safe status in a system It consists of a sensor a logic unit control system and a final controlling element Example A safety instrumented system is made up of an analyzer e g to measure an O2 concentration a PLC and a control
14. e tie ee eee 13 3 2 Safety NGOM ind a 13 3 3 Application restrictions civic a A ad Dd 15 3 3 1 Temperature AO pressure cidad ences A A ana tada De ataa adana da sd 15 3 3 2 abino ULA PANE E L A t 15 3 4 EMO td da dd 16 3 5 Behavior incase Of TAUnS cocina ARA A Aaa aaa 17 3 6 Maintenance and Check arane ano aA E aida 18 3 7 Safety Characteristics iii did abad 20 4 ListOPADDTEViatiONS A a li n 21 Glossa VGA A A a aan 23 Safety Manual Operating Instructions 06 2012 A5E03433511 05 3 Table of contents Safety Manual 4 Operating Instructions 06 2012 A5E03433511 05 Introduction 1 1 1 1 2 Safety Manual Purpose of this document This document contains all information and safety instructions required when using the SITRANS SL in situ gas analyzer in safety instrumented systems It addresses system planners constructors service and maintenance engineers and any personnel commissioning and operating the device Device description SITRANS SL is a gas analyzer employing single line molecular absorption spectroscopy A diode laser emits a beam of infrared light which passes through the process gas and is detected by a receiver unit The wavelength of the laser diode output is tuned to a gas specific absorption line The laser continuously scans this single absorption line with a very high spectral resolution The degree of absorption and the line shape are used for the evaluation The measurement is free of cross i
15. he application specific measuring error under reference condition is 2 of the full scale value For the calculation of the measuring error of the influencing variables and external sensors contact SIEMENS support providing the operating conditions of the measurement point Safety accuracy of the SITRANS SL the maximum effect of a single failure on the measured value which is classified to have no effect The diagnostics function responds within 10 seconds in the worst case scenario A WARNING The mandatory settings and conditions are listed in the Settings Page 16 and Safety characteristics Page 20 sections These conditions must be adhered to in order to fulfill the safety function Safety Manual Operating Instructions 06 2012 A5E03433511 05 13 Device specitic Safety Instructions See also 14 The system component is of type B For detailed information on values and hardware firmware versions refer to the manufacturer declaration for the product Declaration of Conformity Functional Safety according to IEC 61508 and IEC 61511 The combination of sensor automation system and final controlling element forms a safety related system that performs a safety function The emphasis of this description is on the sensor For information on requirements for the automation system or final controlling element refer to the corresponding standards and the extended list of proof tests in Maintenance and che
16. ial number of the original device shall be mentioned The serial number can be found on the nameplate Reference Addresses of the responsible repair center contact partners spare parts lists etc can be obtained from the SITRANS SL Operating instructions sections A 4 and A 5 as well as from the following web address See also web http support automation siemens com Safety Manual Operating Instructions 06 2012 A5E03433511 05 17 Device specific Safety Instructions 3 6 Maintenance and checks Checking the analyzer functions We strongly recommend to check the function capability of the SITRANS SL at regular intervals This can be achieved by use of the verification kit Details of the verification procedure the equipment and the time intervals are described in the operating instructions chapters 9 and 11 Functional safety proof test You should regularly check the safety function of the entire safety circuit according to IEC 61508 61511 The test interval is determined during calculation of each individual safety circuit in a system PFDave The recommended testing interval depends largely on the application but should not exceed one year To detect dangerous faults the SITRANS SL analog output and analog input shall be checked with the following tests Table 3 1 Proof test part 1 Step Action 1 Bypass the safety PLC or take another appropriate action to avoid a fa
17. lse trip 2 Generate or simulate an alarm condition to force the SITRANS SL analyzer to exceed the low alarm current output limit and verify the analog current value e g by disconnecting pressure temperature input 3 Restore the loop to full operation 4 Remove the bypass from the safety PLC and restore to normal operation Table 3 2 Proof test part 2 Step Action 1 Bypass the safety PLC or take another appropriate action to avoid a false trip 2 Carry out an instrument verification according to section 9 1 of the operating instructions 1 3 Restore the loop to full operation 4 Remove the bypass from the safety PLC and restore to normal operation Safety Manual 18 Operating Instructions 06 2012 A5E03433511 05 Device specitic Safety Instructions Table 3 3 Proof test part 3 only required if external sensors are used Step Action 1 Bypass the safety PLC or take another appropriate action to avoid a false trip 2 Select analog input test for Analog Temperature using LUI local user interface 3 Connect a calibrated current source e g a loop calibrator to the analog input O for temperature Note the current measuring instrument used for this test shall provide an accuracy of 0 1 or better 4 Apply at least the following currents in succession 4 0 mA 20 0 mA and a current value within this interval to the analog input The indicated measured values mA shall not deviate more than 0 5 from
18. nal sensor for temperature and pressure must meet the requirements for SIL 1 with a maximum total tolerance safety function of 5 To calculate the error in the concentration measurement which is caused by an error of process temperature and or process pressure measurement contact SIEMENS support providing the operating conditions of the measurement point and the total tolerance safety function of the external sensors 3 3 2 Purging Safety Recommendations for Purging Purging of sensors is always required for applications with oxygen as gas to be measured In this case the sensors require continuous purging using nitrogen For detailed information refer to respective chapters in the user manual Upon installation of the analyzer the use of an external monitoring system must be considered This system must be designed to constantly monitor the purging flow and to ensure that all possible faults are signalled to the Safety PLC Safety Manual Operating Instructions 06 2012 A5E03433511 05 15 Device specific Safety Instructions 3 4 Settings After assembly and commissioning in line with the device manual the following parameter settings shall be made when the devices is used as part of a SIF Safety parameters Enter the following parameter via SITRANS SL LUI setup menu Function Action Temperature correction Set source for temperature compensation Pressure correction Set source for pressure compensation
19. nditions The MTTR after a device fault is 72 hours The logic solver PLC has to be configured to detect low range lt 3 6 mA failure of the SITRANS SL fail low and will recognize these as internal failure of the devices and not cause a spurious trip Certificate of Conformity SITRANS SL Functional Safety http support automation siemens com WW view en 10806991 134200 Safety Manual Operating Instructions 06 2012 A5E0343351 1 05 List of abbreviations List of abbreviations Abbreviations Abbreviation Full term Meaning gt Greater than Mathematical sign for inequality lt Less than Mathematical sign for inequality Percent Mathematical sign for the hundredth part of a whole CO Carbon monixide or A colorless odorless and tasteless gas which is highly toxic to carbonous oxide humans and animals in higher quantities It consists of one carbon molecular formula atom and one oxygen atom connected by a triple bond that consists of two covalent bonds as well as one dative covalent bond In case of SITRANS SL A measuring component DC Diagnostic Coverage Parameter which describes the ratio of the failure rate of detected dangerous failures to the failure rate of all dangerous failures FIT Failure In Time Frequency of failures of the protective function FMEDA Failure Modes Effects and Method to determine out of an overall failure rate of a system the Diagnostic Coverage Anal
20. nterferences since the quasi monochromatic laser light is absorbed very selectively by only one specific line in the scanned spectral range The field design of the SITRANS SL in situ gas analyzer consists of a transmitter unit and a receiver unit The light which is not absorbed by the sample is detected in the receiver The concentration of the gas component is determined from the absorption The individual dependencies of concentration pressure and temperature are application specific An internal reference cell is used to constantly check the stability of the spectrometer thus assuring a continuous self calibration of the analyzer The self calibration of the analyzer is therefore valid for the time period specified in the technical data without the necessity for external recalibration using calibration gases Operating Instructions 06 2012 A5E0343351 1 05 Introduction 1 3 Device variants 1 3 Device variants The following table lists all available SITRANS SL gas analyzer 4 to 20 mA variants which meet the specific safety requirements of IEC 61508 IEC 61511 Product number MLFB Measured component SIL level Assessment type 7MB6221 xAxOx xxxx Oxygen 02 SIL 1 IEC 61508 IEC 61511 FMEDA incl proven in use 7MB6221 xJx0x xxxx Carbon monoxide CO SIL 1 IEC 61508 Hardware assessment FMEDA The term SITRANS SL is used in the following text for all above mentioned devices 1 4 Additional document
21. rther development References If further information on an aspect described here is referenced to the corresponding reference will always be found at the end of a section under See also Safety Manual Operating Instructions 06 2012 A5E0343351 1 05 7 Introduction 1 6 Further information Safety Manual 8 Operating Instructions 06 2012 A5E03433511 05 General description of functional safety 2 2 1 Safety instrumented system This chapter describes the functional safety in general and not specific to a device The devices in the examples are selected as representative examples System description The sensor analyzer logic unit control system and final controlling element combine to form a safety instrumented system which executes a safety function m Le Measured value AS Automation system Final controlling element Shutdown signal Transmitter Analyzer sensor Figure 2 1 Safety related system Functional principle The transmitter generates a process related measured value that is transferred to the automation system The automation system monitors this measured value If the measured value exceeds the range of the high or low limit the automation system generates a shutdown signal for the connected final controlling element which switches the associated valve to the specified safety position Safety Manual Operating Instructions 06 2012 A5E03433511 05 General description of functional safety
22. t taken into account If more than one degree of danger is present the warning notice representing the highest degree of danger will be used A notice warning of injury to persons with a safety alert symbol may also include a warning relating to property damage Qualified Personnel The product system described in this documentation may be operated only by personnel qualified for the specific task in accordance with the relevant documentation in particular its warning notices and safety instructions Qualified personnel are those who based on their training and experience are capable of identifying risks and avoiding potential hazards when working with these products systems Proper use of Siemens products Trademarks Note the following WARNING Siemens products may only be used for the applications described in the catalog and in the relevant technical documentation If products and components from other manufacturers are used these must be recommended or approved by Siemens Proper transport storage installation assembly commissioning operation and maintenance are required to ensure that the products operate safely and without any problems The permissible ambient conditions must be complied with The information in the relevant documentation must be observed All names identified by are registered trademarks of Siemens AG The remaining trademarks in this publication may be trademarks whose use b
23. y third parties for their own purposes could violate the rights of the owner Disclaimer of Liability We have reviewed the contents of this publication to ensure consistency with the hardware and software described Since variance cannot be precluded entirely we cannot guarantee full consistency However the information in this publication is reviewed regularly and any necessary corrections are included in subsequent editions Siemens AG Order number A5E03433511 Copyright Siemens AG Industry Sector 06 2012 Technical data subject to change 2011 2012 Postfach 48 48 All rights reserved 90026 NURNBERG GERMANY Table of contents 1 aaa a aE E ETEO E A A A Ae eats ok eae 5 1 1 Purpose of this document isis it 5 1 2 Device GESCHIPLION ii ida tidad 5 1 3 DEVICE VAMO AA E N a 6 1 4 Additional docuMentatiON ooonnocccnnnncccinonaccccnnononccn ano n cnn E aran rana 6 1 5 O E se heedi a dateeisgedcce ci ae ddcdh i lddeece A agdacged dadeweud dadivensandeeubagdee 7 1 6 Furth SrAnfOrmiatlon tsiscecctsceczecieiascdeelGuadtecesueczeddaczedis vaadtceiSadcnechhida dt 7 2 General description of functional Safety ooonnnccccnnnncccnnnnocnnnnnnnnnnonnnnnnnnnnnnnr cnn nn rre 9 2 1 S fety instrumented System ea ics seers tapes daete Se A aida 9 2 2 Safety integrity level snae a ii id N ANE AA 10 3 Device specific Safety Instructions ooonmocccnninicinnnncncnnnnncccnnnnncnrnnnnnnc nn nece 13 3 1 APPlCAIONS E EE E E A cat suave E ANE at
24. ysis proportion of failures without the potential to bring the safety instrumented system into a dangerous or impermissible functional status SFF and the diagnostic coverage DC according to the requirements to IEC 61508 HFT Hardware Fault Tolerance Capability of a function unit to continue execution of a required function in the presence of faults or deviations IEC International Electrotechnical An international standards organization dealing with electrical Commission electronic and related technologies 1 0 Input Output 1 O refers to the communication between an information processing system such as a computer and the outside world such as a human or another information processing system Inputs are the signals or data received by the system and outputs are the signals or data sent from it LUI Local User Interface User interface for access to Siemens Process analyzers and instruments mA Milliampere A unit of electrical current MLFB Maschinenlesbare German for Fabrikatebezeichnung Machine readable product identification a product code MTBF Mean Time Between Failures Average period between two failures MTTR Mean Time To Repair Average period between the occurrence of a fault on a device or system and its repair NAMUR Normenarbeitsgemeinschaft f r NAMUR is an international user association of automation Mess und Regeltechnik technology in process industries Safety Manual Operating Instructions 06 2012 A5E034335
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