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RESULTS

• Eliminated lightning-induced shutdowns over a three year period

• Improved signal reliability under heavy EMI conditions

• Increased production availability

APPLICATION

Thermal reactor within a sulfur recovery unit where lightning-induced

transients are prevalent

CUSTOMER

Refinery in North America

CHALLENGE

A North American refinery produces valuable light ends, hydrogen sulfide

(H2S), and ammonia. They had been experiencing multiple trips of their

sulfur recovery unit due to high readings (spikes) from grounded

thermocouples and temperature transmitters . These transmitters were

used as safety interlocks in the thermal reactor. Upon investigation, the

root cause pointed toward EMI/lightning induced transients transmitted

either from the grounded thermocouples or field wiring to the field

mounted temperature transmitters. The net result was nuisance interlock

trips, shutdowns and loss of production.

SOLUTION

The refinery installed two Rosemount 644H Smart Head Mount

Temperature Transmitters and the unit has not suffered any lightning

induced shutdowns in over three years.

The Rosemount 644H incorporates a unique diagnostic algorithm

designed to reduce or eliminate the effects of electrical transients, which

can be induced via high voltage process equipment or lightning. The

software solution that is available in every new 644H is called “Open

Sensor Holdoff.” The Open Sensor Holdoff option, at the normal setting,

enables the Rosemount 644H to be more robust under heavy EMI

conditions. This is accomplished by having the transmitter perform

additional verification of the open sensor status prior to activating the

transmitter alarm. If the additional verification shows that the open sensor

condition is not valid, the transmitter will not go into alarm. This software

diagnostic allows the 644 to maintain a good output through most

electrical storms and transients without impacting operations and safety.