Has LEDPOINT® PRS been performance tested by independent laboratories?
LEDPOINT® PRS has been subjected to in-depth performance testing and environmental evaluation by Shell Global Solutions, Micropack Ltd. and SIRA. This has included environmental performance and extended time stability testing as well as basic performance testing. These tests have confirmed the suitability of LEDPOINT® PRS for use in hazardous area environments in both offshore and onshore installations.
Back>> Is LEDPOINT® PRS affected by use in high shock and/or vibration environments?
It is true that early models of LEDPOINT® PRS were affected by shocks caused by de-scaling needle guns being used immediately adjacent to installed units. Whilst these were extreme circumstances the cause was investigated and found to be caused by a passive component shock susceptibility. No vibration susceptibility was found. This component has now been replaced so that now LEDPOINT® PRS units are effectively immune from the effects of both shock and vibration. It is worth noting that the optical components and gas cell assembly were not affected by shocks which were applied in testing at levels that would have been expected to cause failure of the optical source in bulb based optical sensors. A video showing LEDPOINT® PRS operating whilst being subjected to continuous shock applications can be downloaded here w
Back>> How does LEDPOINT® PRS perform in environments with high humidity, mist and fog or when rapid changes of temperature occur?
LEDPOINT® PRS output is unaffected when used in high humidity, mist or foggy conditions at constant temperature. This has been proven in tests conducted in environments up to 99% relative humidity. However in common with all infra-red sensors, either designs with direct focusing optics or with the less satisfactory labyrinthine optical system, the LEDPOINT® PRS output can be affected by condensation caused by rapid environmental temperature changes. It is generally accepted that the most extreme level of rate of temperature rise that is seen in real installations worldwide is 0.33 o C/minute. In common with other professional infra-red based sensors LEDPOINT® PRS is able to function satisfactorily in such environmental conditions which are certainly more extreme than found in UKCS installations. Operation in thick mist conditions and jet washing is shown in video footage on a CD available from AMGas on request or which can be downloaded here.
Back>> Has LEDPOINT® PRS been tested or used in sea salt containing environments?
Yes, LEDPOINT® PRS has both been tested and used in salt mist conditions. Laboratory testing to IEC 68-2-11/BS2011 has been successfully carried out by BRE. LEDPOINT®PRS has also been used extensively in UKCS offshore locations with no adverse effects due to salt deposition or corrosion seen in over four million hours of exposure.
Back>> Over what temperature range will LEDPOINT®PRS
operate ?
Standard LEDPOINT®PRS units are calibrated for operation over the temperature range -20 o C to + 45 o C. Options extend this range to -40 o C to + 45 o C for our low temperature LT variant and to -20 o C to + 70 o C for our high temperature HT variant.
Back>> What is the recommended maintenance interval for LEDPOINT® PRS?
LEDPOINT®PRS units th emselves are self checking and report faults back to the control card so that sensor maintenance is not required. This is supported by field results which have shown, within allowable measurement uncertainty, no change in LEDPOINT®PRS calibration after 3 years field use. However the LEDPOINT®PRS will be part of a larger system which includes cables, connectors etc. which may change with time depending on age, condition and the specific environment. Hence system checking will be required. We recommend starting checking at 6-month intervals and extending this past 12 months as specific site experience is obtained. Note that this is in contrast to any installation, which uses sensors, optical or catalytic, with sinter filters whose functionality cannot be proven without applying a check gas due to the uncertainty of when the sinter filter will be blocked and hence this leads to a fail unsafe situation. In such installations checking at 3-month intervals seems prudent.
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I understand LEDPOINT®PRS gives error reporting to the control card. How does this work?
Yes, LEDPOINT® PRS provides true, fail safe error signalling to the Pellistor control card. The sensor control electronics continually monitor the unit operation and if a fault is detected an output signal approximately equivalent to -100% LEL is generated. The control card will pickup this signal and displays it as a fault, depending on the control card used. In particular, as LEDPOINT® PRS does not contain any sinter filter to impede gas access, it is able to monitor the sensor signals to detect any beam blockage that may have occurred and then signal to the control card that the unit optics need cleaning. In this mode if a gas event occurs this will over-ride the beam block signal and transmit the appropriate gas level reading. It should be noted that any sinter containing sensor cannot give a meaningful beam block indication because it is impossible to confirm whether the sinter is blocked or clear without applying a test gas.
Back>> Does LEDPOINT®PRS respond to narcotic levels of higher hydrocarbons?
Unlike Pellistors LEDPOINT® PRS has a greater response to higher hydrocarbons than to methane. Consequently a standard LEDPOINT® PRS calibrated for methane can give early warning of concentrations of condensate down to narcotic levels if the control card is appropriately set-up. LEDPOINT®PRS actually is more responsive to higher hydrocarbons than any other optical sensor because of the use of an LED light source with specifically tailored spectral characteristics.
Back>> Why has AMGas used an LED light source rather than the more usual filament bulb?
LEDPOINT® PRS has been designed to optimise sensor operational reliability. It was for this reason that LED (light emitting diode) light sources were developed by AMGas for use in the sensor rather than use a filament bulb/thermal light source as found in most optical based sensing products. As well as being inherently more reliable than filament sources LED's do not suffer from the universal filament source problem of unpredictable, catastrophic failure. Accelerated life test measurements on AMGas LED sources have proven an MTBF of in excess of 30 years to half brightness at which point any sensor containing this LED would still be working within specification.
Back>> I want to calculate my system SIL rating, is there any data on LEDPOINT®PRS sensors that can be used and is this based on offshore use?
LEDPOINT® PRS reliability has been assessed based on field use data, component accelerated life testing and generic MIL HBK 217F forecasts. This data gives an un-revealed failure rate of at most 0.033 per annum. This worst-case failure rate has then been used to calculate the unit PFD (probability of failure on demand) based on IEC61508 and then comparing this result with that of a sinter containing sensor (optical or catalytic). These calculations show that in order for the sensor to contribute 10% to a SIL2 system reliability budget, in a 2oo3 (2 out of 3) configuration, then a sinter containing sensor would require checking every 4 weeks whereas LEDPOINT® PRS only needs checking once per annum.
Back>> Can AMGas provide installation support or assist in sensor installation?
AMGas provide telephone support for any installation problems on 0044 (0) 1767 600 590 . We also can carry out offshore system surveys prior to installation to define exact component needs, sensor location definition and advice on infrastructure issues. AMGas also offers an installation service where our team of offshore trained engineers will install LEDPOINT® PRS sensors and check out your system infrastructure with the objective of providing a "Drift free Sensing Solution".
Back>> The LEDPOINT® PRS has "ia" (intrinsically safe) certification so do I need to use it with safety barriers?
No, safety barriers are not needed simply remove the failed Pellistor and replace it with a LEDPOINT® PRS . This is because only part of the unit drive circuitry is "ia" certified, these circuits are powered through safety barriers contained in the LEDPOINT® PRS upper body. This upper body area contains circuits, which are encapsulated and safety certified "m". These "m" circuits interface to the installation Pellistor power and signal wires, which will be connected through an Exe junction box and terminals. "m" certification units are certified for use in Zone 1 and 2 areas, as are units with Exd certification.
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