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Problem statement:

MSP flue gas (O2) Analyzers Control Unit power supply modules frequent failures and

subsequent breakdown of the analyzers.

Make: AMETEK, USA

Model: WDG-IV, Thermox series

Introduction:

The WDG-IV, Thermox series analyzers mounts directly on the combustion process and are

designed for direct measurement in high temperature flue gas applications such as fired heaters

and furnaces, but are equally at home on boilers and other lower temperature applications.

The analyzers are provided with separate Control Unit (Series 2000) for display, Analog output,

and alarms generation & for diagnosis purpose.

Corrective Actions taken

In MSP there are 04nos of AMETEK O2 analyzers. There were frequent failures of powersupply modules 90253VE (P/N 80438SE) Control Unit and subsequent breakdown of theanalyzer. To rectify the same new module was inserted and which worked for few days. After

inserting new power supply modules it was found that Control unit enclosure is getting

overheated, which we suspected was causing the failure of the electronics. Physically on the

electronics no burn & discolor was observed. There are transorbs, installed both on the80438SE/90253VE power supply board and the 80439SE backplane board which are over

voltage protection devices, which can be damaged by a failed power supply over voltagecondition. If these are damaged, they can cause an increased load on the power supply. But,physically transorbs on both the 80438SE power supply board and the 80439SE backplane board

were found ok and no discolor or burn was observed. It is to be noted that Analyzer Control unit

was at air conditioned shelter having temperature: 23-25deg C.

Since, we were running out of stock of spare power supply modules .It is reported to OEM,

Ametek, USA for their help in solving the issue .We had pointed out to M/s Ametek thatoverheating of the module is responsible for the frequent failure. In addition we also pointed out

that the reason for overheating of the module is due to the presence of electrolytic capacitors

very close to the heat sink, the heat was apparently causing them to dry out and fail and becomes

electrically "leaky" over time.

Ametek, USA in their replies informed us the same, which were in line with our observations

that close proximity of electrolytic capacitors with heat sinks are responsible of this kind offrequent failures. In addition Ametek informed that, later in 2009 they had modified power

supply modules in new models of analyzers to do away with the heating issue.

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As, in our case it was old power supply module as analyzer was shipped in February, 2006 &

commissioned in 2006. This frequent power supply failure had happened from October 2010 i.e.

after 4 years of running.(Later on, 2009, Ametek in their design added a cooling fan in the new

modules to dissipate the heat around electrolytic capacitors For an efficient power supply

modules it has to run cooler. The addition of the fan also helps to reduce the power supply

temperature, which results in longer power supply life). The typical life of an electrolytic

capacitor is about 7 years. The normal voltage range is 15.0 to 15.3 volts, maximum 15.8 volts,

although 14.8 volts is not too low to allow the analyzer to operate. If the voltage is under 14.8

volts, there could be too much load, such as could be caused by burned Transorbs.

Since , we were having 17.3 volts, so, around 5 to 6 power supply modules were rectified in-

house by installing new (Al Electrolytic Cap 105C 35V 330uF, Unit Price 68.64Rs& Al

Electrolytic Cap 105C 35V 1000uF, Unit Price 87.62 Rs). These power supply modules are

working very efficiently till now without any problem. The price per unit of a new Power

supply modules Rs. 1, 40, 000.00 as per earlier purchase order.

Picture of Power supply modules