EN 12952-11:2007
(Main)Water-tube boilers and auxiliary installations - Part 11: Requirements for limiting devices of the boiler and accessories
Water-tube boilers and auxiliary installations - Part 11: Requirements for limiting devices of the boiler and accessories
This European Standard specifies requirements for limiters (or limiting devices) which are incorporated into safety systems for water-tube boilers as defined in EN 12952-1.
A limiter (or limiting device) can be either:
- a safety accessory as defined in the Pressure Equipment Directive, Article 1, clause 2.1.3, and needs to include the safety logic and final actuator, or
- one element of a safety system, for example, a self-monitoring water level sensor used as part of a safety accessory as defined in the Pressure Equipment Directive, Article 1, clause 2.1.3. The overall boiler protection function shall be provided in association with additional safety logic (where appropriate) and a final actuator.
The design requirements and examination of functional capability for the limiters are covered in this European Standard.
For an explanation of the extent of the limiter (or limiting device) see Figure A.1.
Wasserrohrkessel und Anlagenkomponenten - Teil 11: Anforderungen an Begrenzungseinrichtungen an Kessel und Zubehör
Diese Europäische Norm legt die Anforderungen an Begrenzer (oder Begrenzungseinrichtungen) fest, die in Sicherheitssystemen für Wasserrohrkessel nach EN 12952-1 eingebaut sind.
Ein Begrenzer (oder eine Begrenzungseinrichtung) kann entweder
ein Ausrüstungsteil mit Sicherheitsfunktion sein, wie in der Druckgeräterichtlinie, Artikel 1, 2.1.3, festgelegt, das mit einer Sicherheitskette und einem Stellglied versehen ist, oder
ein Element eines Sicherheitssystems sein, z. B. ein selbstüberwachender Wasserstandfühler als Teil eines Ausrüstungsteils mit Sicherheitsfunktion nach der Festlegung in der Druckgeräterichtlinie, Artikel 1, 2.1.3. Die Schutzfunktion für den gesamten Kessel wird mit einer zusätzlichen Sicherheitskette (wo angemessen) und
einem Stellglied abgedeckt.
Diese Europäische Norm umfasst die Anforderungen an die Ausführung und die Prüfung der Funktionssicherheit der Begrenzer.
Der Funktionsumfang des Begrenzers (oder der Begrenzungseinrichtung) ist in Bild A.1 verdeutlicht.
Chaudières à tubes d'eau et installations auxiliaires - Partie 11: Exigences pour les dispositifs de limitation de la chaudière et de ses accessoires
Vodocevni kotli in pomožne napeljave - 11. del: Zahteve za omejilne naprave kotla in opremo
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Vodocevni kotli in pomožne napeljave - 11. del: Zahteve za omejevalne naprave kotla in opremeWasserrohrkessel und Anlagekomponenten - Teil 11: Anforderungen an Begrenzungseinrichtungen an Kessel und ZubehörChaudieres a tubes d'eau et installations auxiliaires - Partie 11: Exigences pour les dispositifs de limitation de la chaudiere et de ses accessoiresWater-tube boilers and auxiliary installations - Part 11: Requirements for limiting devices of the boiler and accessories27.060.30Grelniki vode in prenosniki toploteBoilers and heat exchangersICS:Ta slovenski standard je istoveten z:EN 12952-11:2007SIST EN 12952-11:2007en,fr,de01-september-2007SIST EN 12952-11:2007SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12952-11July 2007ICS 27.040 English VersionWater-tube boilers and auxiliary installations - Part 11:Requirements for limiting devices of the boiler and accessoriesChaudières à tubes d'eau et installations auxiliaires - Partie11: Exigences pour les dispositifs de limitation de lachaudière et de ses accessoiresWasserrohrkessel und Anlagekomponenten - Teil 11:Anforderungen an Begrenzungseinrichtungen an Kesselund ZubehörThis European Standard was approved by CEN on 26 May 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12952-11:2007: ESIST EN 12952-11:2007
Limiting device.25 Annex B (informative)
Example of an examination plan.26 Annex C (informative)
Marking of limiters.28 Annex D (normative)
Immunity against electrical and electromagnetic influences —
Requirements and testing.31 Annex ZA (informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 97/23/EC.35 Bibliography.36
techniques — Voltage dips, short interruptions and voltage variations immunity tests (IEC 61000-4-11:2004) EN 61000-6-2:2005, Electromagnetic compatibility (EMC) — Part 6-2: Generic standards — Immunity for in-dustrial environments (IEC 61000-6-2:2005) EN 61508-3:2001, Functional safety of electrical/electronic/programmable electronic safety-related systems — Part 3: Software requirements (IEC 61508-3:1998 + Corrigendum 1999) 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 limiter limiting device that, on reaching a fixed value (e.g. pressure, temperature, flow, water level) is used to inter-rupt and lock-out the energy supply NOTE Limiting device comprises: a measuring or detection function and an activation function for correction, or shutdown, or shutdown and lockout, and which is used to carry out safety related functions as defined in the PED, as on its own or as part of safety (protective) system (e.g. sensors, limiters) (see also Figure 3.1). If this is achieved by multi channel systems, then all items or limit-ers for safety purposes are included within the safety (protective) system.
Figure 1 — Protective devices and safety accessories according to Directive 97/23/EC (PED) 3.2 actuating element component which produces changes in other electrical circuits or volume flows (e.g. fuel, air) as a result of the effect of changes in signal NOTE For example, a gas shut off valve is not an actuating element. 3.3 fail-safe limiter is fail-safe if it possesses the capability of remaining in a safe condition or transferring immediately to another safe condition in the event of certain faults occurring 3.4 self-monitoring regular and automatic determination that all chosen components of a safety system are capable of functioning as required SIST EN 12952-11:2007
necessary facilities 3.6 diversity provision of different means of performing the required function, e.g. other physical principles or other ways of solving the same problem 3.7 complex electronics assemblies which use electronic components with more than one functional output 3.8 safety shut-down process which is effected immediately following the detection of a fault within the limiter or caused by exceeding the threshold of the process value limit resulting in a defined state with deactivated terminals of the safety
output(s) 3.9 lock-out safety shut-down condition of the limiter, such that a restart can only be accomplished by a manual reset of the limiter or by a manual reset of the safety logic and by no other means. This will be achieved by a
competent operator taking account of the physical situation 3.10 sensor transducer which, on reaching a defined limit value, outputs a signal and/or cuts out and only reverses the output signal in the event of a specific change in the performance quantity (e.g. pressure, temperature, flow, level) NOTE Sensors are used for signalling or for triggering control processes. SIST EN 12952-11:2007
General 4.1.1 The requirements set out below shall be followed to ensure uniform assessment of different devices. A limiter shall be such that a single fault in any related part shall not lead to a loss of the safety function. This shall be achieved by fault avoidance techniques such as self-monitoring with redundancy, diversity or a com-bination of these methods. Fault assessment for the electrical components shall be in accordance with 4.4. The fault assessment chart, see Figure 2 shall also be applied for faults in hydraulic, pneumatic and
mechanical components. NOTE The various elements of limiters are given in Annex A. An example of an examination plan is given in Annex B. 4.1.2 Limiters shall function independently of each other and of controls unless their safety function cannot be affected by other such functions. Manual resetting can be realised as a part of the limiter or as a part of the safety logic. Instructions shall be delivered together with the limiter including necessary precautions for a safe installation of it. 4.2
Materials and design 4.2.1 The use of materials with significant differences in their electrochemical potential shall be avoided in order to prevent corrosion which could affect the function of the limiter. 4.2.2 Care shall be taken that if magnetic materials are chosen, they do not adversely affect the working of the limiter. 4.2.3 Parts of the limiter shall be designed to comply with the applicable European Standards. 4.2.4 Limiters shall be capable of withstanding the thermal, mechanical, chemical and electrical loads that can occur during operation. 4.2.5 Limiters shall be designed such that changes in critical circuit component values (such as those
affecting timing) within the component manufacturer's declared worst case tolerances, including the long term stability, shall result in the system continuing to function in accordance with this standard. Compliance shall be checked by worst case analysis. 4.2.6 Limiters using complex electronics For limiters using complex electronics the following requirements apply additionally: • General Systematic errors (built into the design) shall be avoided and random faults (component faults) shall be
controlled by techniques such as self-monitoring with redundancy, diversity or a combination of these methods. • Fault avoidance and fault tolerance The design of the software and hardware shall be based on the functional analysis of the limiter resulting in a structured design explicitly incorporating the control flow, data flow and time related functions required by the application. In the case of custom-chips special attention is required with regard to measures taken to
minimise systematic errors. Software shall be designed using EN 61508-3 to a SIL level (Safety Integrity Level) as determined by analysis according to EN 50156-1. SIST EN 12952-11:2007
Electrical equipment 4.3.1 All wiring and electrical equipment in connection with the limiter shall be adequately protected against the ingress of moisture and the effect of temperature (see [2], [3]). 4.3.2 The function of the limiter and the associated electrical circuit responsible for shutting down and
locking out the heat supply system shall not be affected by other electrical circuits in their proximity. Screened
cables shall be used where necessary (see [2], [3]). 4.3.3 Electrical components within units directly attached to the boiler shall be capable of withstanding a temperature environment resulting from surrounding temperatures of up to 70 °C. Components within units not directly attached to the boiler shall be capable of withstanding an ambient temperature of up to 55 °C. Any equipment that is in contact with parts carrying steam or hot water shall be capable of withstanding the
temperature of those parts. 4.3.4 Devices shall have, as a minimum, a protection rating to IP 54 in accordance with EN 60529. When units are installed inside an enclosure or control box, the IP rating required for the box shall be considered adequate. 4.3.5 All mechanical output contacts of the device shall be of the snap action type. Semi-conductor switches shall have similar characteristics. 4.3.6 The limiter shall tolerate electrical and electromagnetical influences as defined in Annex D. 4.4
Fault assessment 4.4.1 General The limiter, excluding the stored programme section, shall be so constructed that the fault assessment analysis
results in termination. Power failure, breaks in connecting cables and short circuits shall also be considered and
included in the fault assessment analysis. 4.4.2 Fault models and exclusions 4.4.2.1 General With fault assessment in accordance with Figure 2, it shall be assumed that certain faults do not occur. Such assumptions are justified by describing the failure mechanism as well as by stating the conditions
relating to design, construction, environment etc. for the conductors, components and equipment. Faults which shall be taken into account are based on in EN 298:2003, Annex A with consideration of the following faults which may be excluded without further justification: 4.4.2.2 Conductor-to-conductor short circuit fault This fault may be excluded if: a) cables and conductors as specified in EN 50156-1 are used; b) components are encapsulated so that they are moisture resistant or, if they are hermetically sealed and they are capable of withstanding the test specified in EN 50156-1; c) the clearance between live parts shall be designed according to overvoltage category III and pollution degree 3 and the creepage distance shall be designed according to pollution degree 3 but at least for the nominal voltage of 63 V as specified in EN 60664-1; SIST EN 12952-11:2007
multiplied by a safety factor of 0,6. Fault exclusion shall also be permissible if the prospective short circuit
current is less than the nominal current for the contact element concerned. Where contact elements are
connected in series, the contact element with the lowest overcurrent strength shall be the deciding factor. Reed contacts shall not be used. 4.4.2.6 Mechanical failure of switching devices This fault may be excluded if the switching devices are type tested to demonstrate they shall still be operative after at least 250 000 switching cycles under conditions similar to operating conditions. Contactors and relays shall, in addition, be capable of a mechanical endurance of 3 000 000 switching cycles, except for pressure limiters, see Table 2. NOTE The term "conditions similar to operating conditions" covers chemical and climatic influences as well as
electrical and mechanical stresses. 4.4.2.7 Faults in components for safe isolation Faults in components which are provided for safe isolation of electrical circuits (e.g. power circuits and
telecommunications circuits) in accordance with EN 61140 may be excluded. These include: a) inter-winding short circuits in transformers (e.g. primary-secondary). Transformers shall comply with the electrical and mechanical requirements of EN 60742. Except that transformers with working voltages up to 200 V, insulation between windings and insulation against the core shall be designed for a test voltage of 2 kV rms. Transformers shall as a minimum be short-circuit proof. Displacement of windings, turns and connection lines shall be prevented, e.g. by vacuum
impregnation or encapsulation; b) transient voltage of switching devices like relays, contactors or auxiliary contacts between contacts and between coil and contacts. The insulation between contacts or between coil and contact shall be designed for nominal voltages Ub up to 200 V for a test voltage of 2 kV rms and at nominal voltages 200 V < Ub < 500 V for a test voltage of 3,75 kV rms. By special design features (e.g. caps, ribs, encapsulation, banding) at contacts and coils, safe isolation shall also be guaranteed against faults such as spring breakage; c) short-circuiting of isolating distances in optocouplers. SIST EN 12952-11:2007
Marking The limiters shall be marked with the following: manufacturer´s name and/or trademark; year of manufacture; maximum/minimum allowable design limits; unique type reference. NOTE Other markings may be added by the limiter manufacturer or placed in the operating instructions, see
Annex C. SIST EN 12952-11:2007
Key 1 reassessment Figure 2 — Fault assessment chart for limiters excluding the stored programme section SIST EN 12952-11:2007
Components This limiter shall consist of one or more units needed to provide the necessary safety function. The limiter shall comprise of the following elements where applicable: sensor, protection tube or external chamber (see NOTE), timing element, testing devices and other associated equipment up to the terminals of the switching output contacts as shown in Annex A. NOTE Protection tubes and external chambers may be considered to be part of the boiler and in these cases it will be necessary for the limiter manufacturer and the boiler manufacturer to agree on the design and manufacturing
requirements to ensure that the limiter system performs as intended. Examples of water level sensor are: float level switch, electrode probe, conductivity sensor. 5.2
Design 5.2.1 General Chambers, connecting pipes and protection tubes shall be designed so that they: allow free movement in the tube to equalise with the water level in the boiler; can be cleaned and inspected; prevent the build up of sludge in the tubes/chambers. 5.2.2 Internal protection tubes 5.2.2.1 Openings on the protection tube, which are necessary to ensure level equalisation, shall have a minimum diameter of 20 mm or equivalent area but not greater than one-third of the clear bore of the
protection tube, except where specific type approval permits other dimensions. 5.2.2.2 The openings shall be positioned at the lowest point of the bottom and at the highest practicable point of the protection tube. 5.2.3 External chambers 5.2.3.1 The pipe connections to external chambers shall not be less than 20 mm clear bore. It shall be possible to blow down the chambers and connecting pipes to ensure that they do not become blocked. Where applicable, blowdown systems should be fitted with a timing element which prevents the blow down period exceeding a predetermined maximum safe time and monitors the complete move next of the relevant valves and the function of the limiter output contact. 5.2.3.2 If isolating valves are fitted on the connecting pipes to external chambers, an interlock system shall be installed to shut off the heat supply when valves are not fully open. 5.2.3.3 The drain connection of the chamber shall be 15 mm minimum clear bore. 5.2.3.4 Chambers shall be considered as being an integral part of the boiler and need not be blown down if: a) connecting pipes are 100 mm minimum clear bore on the water side and 40 mm minimum clear bore on the steam side and b) connection pipes are less than one metre long and c) there are no isolating valves fitted on the connecting pipes. SIST EN 12952-11:2007
Floating devices 5.3.1 The float shall be guided and shall be able to move freely. 5.3.2 As the actuating force is small, it shall be converted to a positive movement with a minimum of friction. 5.3.3 Mechanical transfer shall be performed in such a way that no sticking can occur. 5.3.4 The magnets shall be protected against the influence of the boiler water (e.g. suspended magnetic particles) by positioning them above the highest operational water level or by the use of an additional shield. 5.3.5 The magnetic materials shall be selected with regard to the temperature and operating conditions, such that the magnetic properties of the materials will not decrease by more than 3 % over a 10 year period. It shall be possible to prove by means of testing equipment integral with the water limiter system, that the mag-netic interaction remains adequate to operate the switch. 5.3.6 Stray magnetic fields shall not adversely influence the magnetic transfer. 5.3.7 The test force for float devices at 15 °C shall be no greater than the total weight of the float and the parts attached to it. 5.4
Level electrode devices 5.4.1 The level electrodes shall be designed, positioned installed and protected in such a way that their proper functioning is not affected by: a) foam and turbulence from the boiler water; b) dirt build up; c) mechanical influences during operation (e.g. vibration); d) positional changes relative to the protection tube and or to other electrodes which could result in a short circuit. 5.4.2 Unless the manufacturers fault assessment shows that an equivalent degree of safety is maintained: the minimum air distance between measuring electrodes to earth and to each other inside the pressure part shall be 14 mm; level electrode devices shall be installed vertically or at inclinations of up to 45° from the vertical. 5.4.3 Devices that are used to support or restrict movement of the electrode shall be included in the exami-nation of functional capability (see 5.5). 5.4.4 The maximum operating voltage of electrodes shall be 50 V a.c. rms without a d.c. component which could cause significant polarisation effects. If galvanic isolation from the main supply is required, it shall be provided by a safety transformer in accordance with EN 60742, meeting the requirements of class of
protection II (double insulation). 5.4.5 The earth return connection shall be as close as possible to the electrode. 5.4.6 The manufacturer of the limiter shall define the limits of application with respect to the water
conductivity. SIST EN 12952-11:2007
insulation resistance caused for example, by dirt build up on the insulator or internal leakage of the electrode, the system shall go into a safe state. 5.4.8 Only one low water limiter shall be permitted to be installed within the protection tube or an external chamber. It is acceptable, however, to install additional electrodes for control and other alarm functions. 5.5
Examination of functional capability The examination of the functional capability of the limiter shall be in accordance with the procedures given in
Table 1.
A.1 Environmental influences Check operation of the water level limiter under the following conditions, either by certified test document review, simulation, on a test boiler or in any combination.
— power supply variation test; — power supply interruption test; — frequency variation test; — EMC immunity test; — ambient temperature test; — IP rating. Annex D EN 50156-1 A.2 Test of independent function-ing When common components are shared, a failure of the second limiter or the control circuit(s) shall be simulated. The safety function of the
limiter shall not be affected. A.3 Thermal cycle test The whole limiter assembly shall be subjected to at least 100 thermal cy-cles at full pressure by the manufacturer.
During each cycle, the limiter shall be shown to operate to the manufac-turer's specification at the lowest temperature and highest temperature, allowing sufficient soak time at both these conditions.
In the case of electrode devices, immediately after completing the cyclic test, the insulation resistance of all insulated parts of the electrode shall be measured. No steam leak shall be
permitted.
The resistance shall be more than 10 MΩ at test voltage of 500 V d.c. under room conditions. A.4 Final performance test This shall consist of a comprehensive series of measurements and observations of the characteristics and performance of the water level limiter to demonstrate that no unacceptable deterioration has occurred as a result of previous tests. Tests shall be done at ambient temperature at normal voltages and subsequently with the worst combination of supply voltages. In the case of electrode devices, the water level limiter shall be checked for correct operation within the maximum and minimum water conductivities as specified by the manufacturer. The water level limiter shall
initiate alarm signals when the level drops below the low water level at for each of the max. and min. water conductivities. SIST EN 12952-11:2007
DEVICES
B.1 Testing of internal faults Failure of each critical component shall be simulated and a check shall be made to show that the water level limiter goes to a safe state in accordance with the relevant fault assessment charts. By way of examples "Internal Faults" are: a) short circuit or interruptions in components such as in resistors,
capacitors, discrete and integrated semi-conductor elements etc.; b) faulty oscillations of electrical circuits; c) non-opening or non-closing of electromagnetic components, such as
contactors, relays etc.; d) short circuits or interruptions in control circuits, such as broken wires,
earth fault and conductor-to-conductor short circuit etc.; e) software errors; f) systematic hardware faults in integrated circuit components. Compliance with 4.4. B.2 Insulation resistance test A check shall be made of the resistance between all insulated parts of the limiter circuits, which includes contacts of switches, relays or contactors for isolation functions. The resistance shall be more than 10 MΩ at test voltage of 500 V d.c. under room conditions. B.3 Test for maximum operating
voltage Electrode shall be subjected to maximum voltage. 50 V a.c. rms maximum. C FLOATING DEVICES
C.1 Durability test on electrome-chanical switches Electromechanical switches shall be life tested to at least 100 000 opera-tions at full rated temperature and full rated electrical load. At least one sample shall be with the maximum rated a.c. inductive load, and another with the maximum rated d.c. load. The electromechanical switches shall still be
functional at the end of
the test cycle. C.2 Test for free movement of the float The difference in diameter between the outside of the float and the inside of the chamber or guide tube shall be checked. The difference shall not be less than 10 mm. C.3 Test for positive movement of the float A check shall be made to ensure that the mechanical parts which are subjected to wear shall be shown to work for a minimum of 250 000 operations within the full range of the mechanical movement. The limiter shall not mal-function during the test
cycle. SIST EN 12952-11:2007
Fault detection 5.6.1 The limiter shall be tested automatically and periodically during use to ensure that the safety is not impaired by at least one of the following methods: a) incorporating a self testing device; b) lowering or increasing the water level; c) sinking or raising the float device. 5.6.2 The safety shutdown signal shall be initiated if the test sequence fails. 5.6.3 Manual functional testing of the limiters shall be possible at any time under any operating conditions, e.g. by simulation where appropriate. The result of the test shall be clearly indicated to the boiler operator. 6 Special requirements for pressure limiters 6.1
Components The limiter shall consist of one or more units needed to provide the necessary safety function. The limiter shall comprise of the following units where applicable: connecting piping, body, sensor, external chamber, timing
element, testing devices and other associated equipment up to the terminals of the switching output contacts as shown in Annex A. 6.2
Additional fault assessment requirements In addition to the requirements in 4.4, it may be assumed that failure of the component shall not occur where a mechanical component of the pressure limiter has been designed for a dynamic load and has been
successfully tested for 2 000 000 cycles over its full range of mechanical movement. 6.3
Design 6.3.1 The limiter shall be capable of withstanding an overload of at least 1,5 times its maximum adjustable pressure without detriment to its accuracy. The manufacturer may state a higher overload pressure. 6.3.2 The adjustment of the set pressure shall only be possible by means of a tool. Any adjustment shall be capable of being secured so that it does not alter due to any environmental influence, e.g. vibration. The set pressure shall be indicated on a scale. 6.3.3 It shall not be possible to adjust the set pressure to such an extent that the limiter loses its function (e.g. by the spring becoming coil-bound). 6.3.4 Connecting pipes for the limiter on steam boilers shall be connected to the steam space of the boiler. If necessary the limiter shall be protected from the steam temperature by a water seal. For fully flooded hot water generators the limiter shall be connected to the supply pipe before the first shut-off valve. If isolating valves are fitted on the connecting pipes, an interlock system shall be installed to shut off the heat supply when valves are not fully open. 6.3.5 If there is the possibility of sludge build-up in the connecting pipe it shall be possible to purge the pipe. Such purging shall not remove the water seal or introduce dirt into the water seal. 6.3.6 The limiter body shall be installed vertically so that dirt does not enter the limiter. SIST EN 12952-11:2007
Electrical equipment Electrical equipment shall conform to the relevant clauses of EN 60730-1 (see Table 3). 6.5
Examination of functional capability 6.5.1 The deviation from the set pressure when type tested as specified in 6.5.2 to 6.5.6 shall not exceed the higher of: ± (2 % of the span + 1 % of the full scale) or
± 0,04 bar. The span is the difference between the lowest and the highest set pressure indicated on the scale. Full scale means the highest set pressure indicated on the scale. 6.5.2 The test required for the test procedure shall be in accordance with Table 2 and Figure 3. Table 2 — Test procedure Clause reference Adjust-ment Number of cycles Pressure Tempe- rature Upper Switching Point (USP) high pressure limiter Lower Switch-ing Point (LSP) low pressure limiter Requirements in accordance with 6.5.1 20 °C USP 1 LSP 1 6.5.4 Lowest value Minimum 1 Switchingpressure 70 °C USP 2 LSP 2 Compare USP 1/USP 2or LSP 1/LSP 2 20 °C USP 3 LSP 3 6.5.5 Highest value Minimum 1 Switching pressure 70 °C USP 4 LSP 4 Compare USP 3/ USP 4 or LSP 3/LSP 4 Minimum 1 Switching pressure 20 °C USP 5 LSP 5 6.5.6 Lowest value 100 Maximum overload 20 °C USP 6 LSP 6 Compare
USP 5/ USP 6 or LSP 5/LSP 6 6.2
Mid point of the span 2 × 106 To give full mechanical movement20 °C — — No
mechanical damage
Key 1 pressure 2 falling 3 rising pressure USP is the Upper Switching Point (relevant for the high pressure limiter)
LSP is the Lower Switching Point (relevant for the low pressure limiter) Figure 3— Switching point for pressure limiter 6.5.3 The repeatability shall be within the limits stated in 6.5.1 when the tests detailed in 6.5.4, 6.5.5 and 6.5.6 are carried out using air as the test medium. The pressure shall not be changed at a rate faster than the span of the limiter in one minute. 6.5.4 The set pressure shall be adjusted to the lower end of the set pressure scale and the switching pres-sure measured at an ambient temperature of 20 °C. The ambient temperature shall be raised to 70 °C and the switching pressure measured. 6.5.5 The test in 6.5.4 shall be repeated with the set pressure at the upper end of the set pressure scale. 6.5.6 The set pressure shall be adjusted to the lower end of the set pressure scale and the switching pres-sure measured at an ambient temperature of 20 °C. The pressure shall be changed 100 times f
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