Duplicated temperature monitoring in single unit

An Emerson Process Management - Rosemount Measurement product story

Edited by the Engineeringtalk editorial team Jun 27, 2000

Fisher-Rosemount has introduced the latest version of the Model 3244MV Multivariable Temperature Transmitter to achieve duplicated temperature monitoring in one overall housing

To ensure plant safety, and product quality, reliable temperature measurement is essential.

Because of occasional failures of the sensing element itself, it is often a plant requirement to have duplicated temperature monitoring systems, with a logic system to choose the valid reading.

Fisher-Rosemount has introduced the latest version of their Model 3244MV Multivariable Temperature Transmitter to achieve this duplication in one overall housing, at minimal extra cost compared to a standard unit.

The 3244MV has the facility for accepting two sensor inputs into the one transmitter, which can then be used to provide a variety of enhanced features.

The 4-20mA analogue output is derived from the first sensor.

If for any reason the transmitter electronics identifies a sensor failure, then the "Hot Back Up" feature sets the transmitter to seamlessly switch to sensor two - with no upset to the analogue signal.

A warning message will be displayed, and communicated via the HART, FOUNDATION fieldbus or Profibus PA protocols, that sensor 1 has failed, so enabling maintenance to be scheduled, and more importantly, the process to keep running.

Initial tests have shown that for a 5% increase in cost, compared to a traditional single element sensor, the temperature point failure risk is reduced by 48%, giving users vastly increased plant availability.

The Sensor Drift Alert feature of the 3244MV aids in the prediction of sensor failure and should be used when measuring the same process temperature, such as with a duplex element sensor.

The transmitter will compare the output of the two sensors, the differential of which should be close to zero (+/- tolerances on sensors).

The user can set the maximum allowable temperature difference (drift) between the two sensors.

When the transmitter detects a temperature difference greater than the specified maximum, a warning message will be displayed and communicated again via the HART, FOUNDATION fieldbus or Profibus PA protocol.

With two sensor inputs, the transmitter can also be configured to output the Differential temperature between the two sensors, or alternatively the average temperature of the two sensors.

The individually sensed temperature from each sensor is also available as a digital output using the HART, FOUNDATION fieldbus or Profibus PA protocols.

The intelligent electronics which use surface mount technology and a digital ASIC for highest reliability, can also be configured to work on a combination of the enhanced options detailed above.

For critical applications such as safety interlocks and control loops, the output can be set to provide the average of the two measurements and send an alert if the temperature difference exceeds the set maximum differential.

If for any reason the transmitter detects a sensor failure, an alert will be sent and the primary variable will hold the measurement of the working sensor.