MICHELL Instruments XTC 601 Binary Gas Analyzer for Hydrogen Monitoring Instruction Manual
- June 4, 2024
- MICHELL Instruments
Table of Contents
XTP/XTC 601
SIL Safety Manual
Note: Supplement to the instruction manual
l97587 Issue 1.2 September 2022
Michell Instruments
For Michell Instruments’ contact information please go to www.michell.com
© 2022 Michell Instruments
This document is the property of Michell Instruments Ltd and may not be copied
or otherwise reproduced, communicated in any way to third parties, nor stored
in any Data
Processing System without the express written authorization of Michell
Instruments Ltd.
The contents of this safety manual shall not become part of or modify any
prior or existing agreement, commitment or legal relationship. All obligations
on the part of Michell Instruments 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.
XTP & XTC SIL Safety Manual
NOTE: This product must not be modified or altered in any way. Unauthorized
change is not permitted and to do so would cause Functional Safety, as
confirmed by the
IEC61508 assessment, to be null-and-void. The design of This product is
strictly controlled and to do so would invalidate all approvals,
certifications and warranties this product
holds. Please consult Michell Instruments Ltd directly for any functionality
or service queries you may have.
Safety Guidelines
This manual relates only to the SIL aspects of this product.
For all other operation, installation & maintenance information refer to the
product manual. The user must not use this equipment for any other purpose
than that stated. Do not apply values greater than the maximum value stated.
This manual contains information relating to the SIL aspects of operating this
product. Use competent personnel using good engineering practices for all
procedures in this manual.
Qualified Personnel
This product should only be set up and used in conjunction with this documentation. Commissioning and operation of this product should only be performed by qualified personnel.
Abbreviations
The following abbreviations are used in this manual:
λ | Failure Rate |
---|---|
λD | Dangerous Failure Rate |
λDD | Dangerous Detected Failure Rate |
λDU | Dangerous Undetected Failure Rate |
λs | Safe Failure Rate |
/hr | Per Hour |
ADC | Analogue-To-Digital Converter |
DAC | Digital-To-Analogue Converter |
DC | Diagnostic Coverage |
E/E/PE | Electrical/Electronic/Programmable Electronic |
EMF | Electromotive Force |
ESC | Engineering Safety Consultants |
EUC | Equipment Under Control |
FIT | Failure in time |
FREDA | Failure Mode Effect and Diagnostics Analysis |
FMR | Failure Mode Ratio |
FS | Functional Safety |
FSM | Functional Safety Management |
HFT | Hardware Fault Tolerance |
MDT | Mean Down Time |
MTTR | Mean Time To Restoration |
NPRD | Non-Electronic Parts Reliability Data |
O2 | Oxygen |
O/C | Open Circuit |
PFD | Probability of Failure on Demand |
Average Frequency of a Dangerous Failure per Hour | |
PLC | Programmable Logic Controller |
PTI | Proof Test Interval |
QA | Quality Assurance |
RBD | Reliability Block Diagram |
S/C | Short Circuit |
SFF | Safe Failure Fraction |
SIF | Safety Instrumented Function |
SIL | Safety Integrity Level |
SR | Safety Related |
Tp | Proof Test Interval |
INTRODUCTION
1.1 General
This manual refers only to:
XTP601 Oxygen Transmitter.
XTP601 Oxygen Analyzer.
XTC601 Binary Gas Analyzer.
XTC601 Binary Gas Transmitter.
There are derivatives of each model as shown in the below table:
Analyzer Name | Type |
---|---|
XTP601-GP1 | General purpose analyzer with display |
XTP601-GP2 | General purpose analyzer with flame arrestors |
XTP601-EX1 | Hazardous area analyzer with display |
XTC601-GP1 | General purpose analyzer with display |
XTC601-GP2 | General purpose analyzer with flame arrestors |
XTC601-EX1 | Hazardous area analyzer with display |
1.2 Required documentation
This document only applies in conjunction with the following documentation:
Analyzer Name | Type | Document No. |
---|---|---|
XTP601 | Process Oxygen Analyzer User’s Manual (UK) | 97313 |
XTP601 | Binary Gas Analyzer User’s Manual (UK) | 97400 |
NOTE: For each type, there are manuals with the same content translated
into other languages.
This document contains SIL-related data that will be required when using the
XTP601 & XTC601 products in safety-instrumented systems.
It is aimed at system planners, constructors, service and maintenance
engineers and personnel who will commission the device.
SAFETY INSTRUCTIONS
These products are intended for use in safety applications.
All safety instructions relate exclusively to the analog output signal
(4–20mA). The products are certified to SIL2 (IEC 61508). The product’s
software is certified SIL2
(IEC61508). The use of these products integrated in to safety-related systems
is therefore possible.
Definition: Safety-instrumented system
A safety-instrumented system executes the safety functions that are required
to achieve or maintain a safe status in a system. It consists of a sensor,
logic unit/control system
, and final controlling element. A Safety Instrumented System (SIS) could be
made of an analyzer (e.g. XTP 02 Concentration), a Safety rated logic Solver
(e.g. safety relay or safety-rated PLC) and a final element (e.g. valve, or
alarm with defined response). Definition: Safety function
The defined function is executed by a safety-instrumented system with the
objective of achieving or maintaining a safe system considering a defined
dangerous occurrence.
Example: XTP O2 concentration above or below a defined threshold.
2.1 Safety Integrity Level (SIL)
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 in a
safety function. The higher the SIL of the safety-instrumented system, the
higher the probability that the required safety function will work.
The achievable SIL is determined by the following safety characteristics:
- Average probability of dangerous failure of a safety function in case of demand (PFDAvG)
- Hardware fault tolerance (HFT)
- Safe failure fraction (SFF)
Description: 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 (PFDAvG). The table deals with “Low demand mode”, i.e. the safety function is required a maximum of once per year on average.
SIL level | PFDavg |
---|---|
SIL 4 | 10–4 > PFDavg ≧ 10–5 |
SIL 3 | 10–3 > PFDavg ≧ 10–4 |
SIL 2 | 10–2 > PFDavg ≧ 10–3 |
SIL 1 | 10–1 > PFDavg ≧ 10–2 |
Table 1 Safety Integrity Level
The “average probability of dangerous failures of the entire safety-
instrumented system” (PFDAvG) is normally spilt between the entire SIL
system.
The following table shows the achievable Safety Integrity Level (SIL) for the entire safety instrumented system for type B systems depending on the proportion of safe failures (SFF) and the hardware fault tolerance (HFT). XTP and XTC units are considered Type B due to their complexity. Type B systems also include sensors and positioners actuators with complex components, e.g. microprocessors (see also IEC 61508, Section 2).
SFF | HFT |
---|---|
0 | 1 |
<60% | Not allowed |
60 to 90% | SIL1 |
90 to 99% | SIL2 |
>99% | SIL3 |
Table 2 Safety Integrity Level
DEVICE-SPECIFIC SAFETY INSTRUCTIONS
3.1 Applications
The Hardware assessment of the XTP601 & XTC601 shall provide the safety
instrumentation engineer with the required failure data as per IEC 61508.
The hardware of XTP601 & XTC601 satisfies the requirements in terms of
functional safety to SIL 2 in accordance with IEC 61508. The XTP601 & XTC601
is usable in safety
applications to monitor limits.
3.2 Safety Function
The XTP601 & XTC601 are mainly used for user-defined threshold monitoring.
The XTP601 Process Oxygen Analyzer was assessed against the following safety
function:
-
Ability to detect oxygen presence within another gas stream and generate a 4–20mA output.
The XTC601 Binary Gas Analyzer was assessed against the following safety function: -
Ability to detect target gas in another gas stream and generate a 4–20mA output.
Warning
See the “Settings” and “Safety characteristics” sections for the binding
settings and conditions. These conditions must be met to fulfill the safety
function. When the safety function has been executed, safety-instrumented
systems with no self-locking function should be brought to a monitored or
otherwise safe status within the Mean Time To Repair (MTTR). The MTTR is 168
hours. For full product information refer to User Manuals 97313 & 97400.
3.3 Settings
After installation and commissioning (refer to User Manuals), the following
parameter settings should be made for the safety function:
Safety parameters
Function|
---|---
Analog Output| Select 4–20mA (NAMUR)
Protection against configuration changes
After configuration, the menu access codes of XTP601 & XTC601 shall be changed
so that the device is protected against unauthorized changes and operation.
Checking the safety function after installation After installation a safety
function test must be carried out.
Using reference gas, i.e. N2 , 4mA must be measured at the analog output.
For the test of the safety function, it is fundamental to use a second
reference gas with a defined proportion of oxygen. The results of the
measurement must be within a range
of ±5% (full span) of the expected result.
3.4 In case of faults
Fault
The procedure in case of faults is described in the User Manuals.
Repair
The defective product should be sent to a Michell Instruments Service
Department with details of the fault and the cause. When ordering a
replacement product, please specify the serial number of the original product.
The serial number can be found on the nameplate. Information regarding the
location of Michell Instruments Service centres can be found at the following
web address: www.michell.com
3.5 Maintenance/Calibration
We recommend that the functioning of the XTP601 & XTC601 is checked at regular
intervals of one year.
Check at least the following: Test the basic functionality of the XTP601 &
XTC601 as described in the User Manual.
Checking safety
You should regularly check the safety function of the entire safety circuit in
line with IEC 61508/61511.
The testing intervals are determined during the circulation of each individual
safety circuit in a system. The recommended prove interval depends on the
application but it
should be at least once a year. To detect dangerous undetected faults, the
XTP601 & XTC601 analog output shall be checked with the following test:
To execute the safety proof test both tests (1 and 2) must be performed. Proof
test 1 consists of the steps described in the table below.
Step | Action |
---|---|
1 | Bypass the safety PLC or take other appropriate action to avoid a false |
trip.
2| Generate or simulate an alarm condition to force the product to go to the
high alarm current output and verify that the analog current reaches that
value.
3| Generate or simulate an alarm condition to force the product to go to the
low alarm current output and verify that the analog current reaches that
value.
4| Restore the loop to full operation.
5| Remove the bypass from the safety PLC or otherwise restore normal
operation.
Proof test 2 consists of the steps described in the table below.
Step | Action |
---|---|
1 | Bypass the safety PLC or take other appropriate action to avoid a false |
trip.
2| Perform Proof Test 1.
3| Perform a 2-point calibration of the product.
4| Perform a reference measuring with at least one measuring point between min
and max concentration. You must use a calibration gas with a well-known gas
concentration. The expected result must have a tolerance of not more than 5%.
5| Restore the loop to full operation.
6| Remove the bypass from the safety PLC or otherwise restore normal
operation.
This test will detect more than 90% of possible “du” failures in the product.
Should faults be detected, the product should not be used until completely
rectified.
3.6 Safety Characteristics
The safety characteristics necessary for use of the system are listed in the
SIL declaration of conformity (see Appendix A.1). These values apply under the
following conditions:
- The XTP601 & XTC601 are only used in safety-related systems with a low demand mode for the safety function.
- The safety-related parameters/settings (see “Settings” section) have been entered by local operation and checked before commencing safety instrumented operation.
- The XTP601 & XTC601 is blocked against unwanted and unauthorized changes/ operation.
- The maximum operating temperature is +40°C for the XTC601 and +55°C for the XTP601.
- All used materials are compatible with process conditions.
- The MTTR after a device fault is 168 hours.
- The logic solver (PLC) must be configured to detect over range (>21mA) and under range (<3.6mA) failure of the XTP601 & XTC601 (Fail High and Fail Low) and will recognize these as internal failures of the products and not cause a spurious trip.
Also see the Settings section of this manual and Appendix below.
Appendix A
A.1 SIL Declaration of Conformity
ENGINEERING SAFETY CONSULTANTS
The Global Provider of Functional Safety Expense and Technical Consultancy
Random Hardware Reliability and Systematic Assessment Certificate
Functional Safety of Safety-Related Programmable Electronic Systems
The Michell Instruments UK Ltd, XTP601 Process Oxygen Analyser & XTC601 Binary
Gas Analyser have been assessed and are considered capable for use in a low-
demand Safety Function up to (and including) SIL 2 capability with regards to
systematic, random hardware failures and architectural constraints.
The assessment was based on the assumptions, data provided, and
recommendations given in:
-
Engineering Safety Consultants Ltd Report: H215_FM001 rev. 4.
The products were assessed against the following failure modes: -
XTP601: Ability to detect oxygen presence within another gas stream and generate a 420mA output;
-
XTC601: Ability to detect target gas in another gas stream and generate a 4-20mA output.
The assessment was carried out to determine compliance with IEC 61508 (2010 Edition) with regards to: -
Random Hardware Failure (Predicted PFD as shown in Table below) with a Mean Down Time (MDT) of 168 hours, a Proof Test Interval (PTI) of one year (8760 hours), a Proof Test Coverage of 95% or 90% and an Overhaul Interval of 10 years (87600 hours);
-
Random Hardware Failure with Achieved PFH:
o XTP601 = 5.4E-08
o XTC601 = 3.9E-08 -
Random Hardware Failure with Achieved DD:
o XTP601 = 7.4E-07
o XTC601 = 7.0E-07 -
Random Hardware Failure with Achieved DU:
o XTP601 = 5.4E-08
o XTC601 = 3.9E-08 -
Architectural Constraint (Type B, SFF >90%, <99%), HFT = 0;
-
Systematic SIL 2 capability against IEC 61508 (2010 Edition) Parts 1, 2 and 3.
Device| Proof Test
Coverage
(PTC)| PFD Target
(20% of SIL
2 band)| AchievedPFD| Estimated
Achieved
PFD| SFF| Type| Estimated
Achieved
SIL (Arch)| Estimated
Overall SIL
Capability
---|---|---|---|---|---|---|---|---
XTP601| 95%| 2.E-03| 4.E-04| 2| 94%| B| 2| 2
90%| 5.E-04| 2| 2| 2
XTC601| 95%| 2.E-03| 3.E-04| 2| 96%| B| 2| 2
90%| 4.E-04| 2| 2| 2
IMPORTANT: It should be noted that this assessment does not include confirmation of the response time of the device. For response times (along with any relevant assumptions) reference should be made to the Safety Manual of each device and the total SIF response time MUST be compared against the process safety time for the specific application.
Managing Director: Simon Burwood
Member of IEC 61508 (MT61808-1-2) & IEC 61511 (MT61511) Maintenance Committees
Assessment Date: February 2020
Renewal Date: August 2022, valid to August 2024
Certificate: H215_CT001 rev. 3
A.2 Engineering Safety Consultants Limited. London, UK Test Report extract
2.1 General
This report provides a Prior Use Assessment of the Michell Instruments UK Ltd,
XTP601 Process Oxygen Analyzer and XTC601 Binary Gas Analyzer, as defined in
the Prior
Use requirements in IEC 61511 (2nd Edition) Clause 11.5.3 and 11.5.4 [2]
including an estimation of Probability of Failure on Demand (PFD), Safe
Failure Fraction (SFF) and a review of the systematic capability as supporting
evidence for avoidance and minimization of systematic failures.
A Failure Mode Effects and Diagnostics Analysis (FMEDA) was conducted on the
XTP601 & XTC601 to estimate the random hardware failure rate in order to
assess suitability for use in a safety function with regards to the PFD and
the architectural requirements in terms of Hardware Fault Tolerance (HFT) and
SFF, using the approach detailed in Route
1H in IEC 61508-2 [1].
2.2 Hardware Reliability Verification
These devices will form part of the sensor element sub-system of a Safety
Instrumented Function (SIF) and thus an assessment was conducted to
demonstrate its capabilities in
terms of PFD. The remaining sensing, logic solver and final element sub-
systems were excluded from the assessment, in order to allow for their PFD
contributions, the devices
were assessed against 20% of Safety Integrity Level (SIL) 2 PFD band (e.g. SIL
2 band modified to 2.0E-03).
The analysis was based on the assumption that repairs would be carried out
with a Mean Down Time (MDT) of 168 hours, a Proof Test Interval (PTI) of one
year (8760
hours) and capable of revealing 100% of undetected failures.
The XTP601 Process Oxygen Analyzer was assessed against the following safety
function:
-
Ability to detect oxygen presence within another gas stream and generate a 4–20mA output.
The XTC601 Binary Gas Analyzer was assessed against the following safety function: -
Ability to detect target gas in another gas stream and generate a 4–20mA output.
Table 3 shows a summary of the results of the XTP601 & XTC601 based on the data provided and the assumptions given in this report. The full set of results for the hardware reliability verification is presented in Table 4.
Device| PFD Target (20%
of SIL2 band)| PFD achieved| PFD achieved
(SIL)| SFF| Type| Achieved SIL (Architecture HFT =0)|
Overall achieved
SIL
---|---|---|---|---|---|---|---
XTP601| 2.E-03| 4.E-04| 2| 94%| B| 2| 2
XTC601| 2.E-03| 3.E-04| 2| 96%| B| 2| 2
Table 3 SIL Results Summary
APPENDIX A
Device Reference | XTP601 & XTC601 |
---|---|
Function Specification | XTP601 Oxygen Transmitter XTC601 Binary Gas Analyzer |
Software Configuration/Settings | As per customer order |
Verson ion | Firmware for XTP601: 36217 V1.09 Firmware for XTC601: 37701 V1.06 |
Hardware Diagram version | XTP601: 80895/C V2.0 XTC601: 81003/C V1.0 |
Hardware Configuration/Settings | As per customer order |
Failure Mode(s) Definition | Dangerous detected |
rate per hour
Dangerous undetected| dangerous undetected failure rate per hour
Safe| safe (or spurious) failure rate per hour
Estimated failure rate| XTP601 7.0E-07, XTC601 5.9E-07
Dangerous Undetected Failures (ADU)| XTP601 5.41E-08, XTC601 3.87E-08 (FIT/hr)
Dangerous Detected Failures (ADD)| XTP601 7.39E-07, XTC601 7.00E-07 (FIT/hr)
Safe Failures (AS)| XTP601 & XTC601 1.57E-07 (FIT/hr)
Probability of Failure on Demand (PFD)| XTP601 3.6E-04, XTC601 2.9E-04
Safe Failure Fraction (SFF)| XTP601 94% XTC601 96%
Hardware Fault Tolerance (HFT)| 0
Classification (Type A or Type B)| B
Demand (Low demand or High Demand)| Low
Proof Testing Procedures| See section 3.5
Installation| Refer to User Manual 97313 (XTP) & 97400 (XTC)
Average lifetime of device (yrs)| 5
Environmental Profile| Max +50°C. 80%rh>31°C/50%>+50°C
Systematic/Proven in Use Safety Integrity Level| 2
Assumptions| Refer to User Manual
General Notes and applicable regulations| This product complies with
applicable standards and clauses of EU ATEX, EMC, PED Directives. Refer to the
EU Declaration supplied with each product for full details of the latest
versions.
Testing requirements| See section 3.5
Table 4 Verification Results
NOTES……….
ENGINEERING SAFETY CONSULTANTS LTD
2nd Floor, Exchequer Court, 33 St. Mary Axe,
London, EC3A 8AA UK
Telephone/Fax: +44 (0)20 8542 2807
E-Mail:info@esc.uk.net Web:
www.esc.uk.net
Registered in England and Wales: 7006868
Registered Office: 33 St. Mary Axe, London, EC3A 8AA
www.ProcessSensing.com
http://www.michell.com
Documents / Resources
|
MICHELL Instruments XTC 601 Binary Gas Analyzer for Hydrogen
Monitoring
[pdf] Instruction Manual
XTC 601 Binary Gas Analyzer for Hydrogen Monitoring, XTC 601, Binary Gas
Analyzer for Hydrogen Monitoring, Hydrogen Monitoring, Gas Analyzer, Analyzer
---|---
References
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- Functional Safety Expertise | Engineering Safety Consultants
- Michell Instruments, Dew Point, Humidity and Oxygen Specialists
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