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Dispelling the myths of HART-enabled devices
Even though millions of HART-enabled field devices are installed in locations around the world, myths and misconceptions about this powerful technology for control systems abound.
04/19/2005
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Users Be Aware
Intelligent data is no longer available only through the handheld communicator or a proprietary program, but can be monitored continuously 24 hours a day, 7 days a week.
Through the continuous monitoring of the HART Communication digital signal, potential control system failures can be easily detected at the device level. HART-detectable failure scenarios include in-range sensor failures, 4-20mA distortion (analog output does not equal PV measurement), incorrect setup or a device calibration mismatch (device span does not equal span on control system).
The continuous monitoring of HART data can be crucial to a plants operation. Recently one major US chemical company could have averted a three-day shutdown due to an in-range failure of a level control loop that went undetected. Investigation showed water had migrated into the level transmitter partially shorting out the analog output, resulting in erroneous level measurement signals being receive in the control room. Had the control system been monitoring the HART Communication signal it would have detected this failure within seconds by comparing the digital value of the PV versus the represented analog value. Determining a PV mismatch, the system could have alerted the operator and potentially saved over $300,000 in downtime.
By using a continuously monitored HART enabled-system, in addition to failures it is also possible to detect anomalies such as when a devices setup has been changed, a self-test run or a reset has been performed in the field, logging the information for audit trail purposes.
New control, safety and asset management systems capitalize on the intelligent information each HART-enabled device contains. HART-enabled system solutions retrieve important status and diagnostics information helping keep your plant systems safe. It is important to close the &ldquoinformation gap&rdquo that exists by using the 4-20mA analog signal without using the digital information available on every HART-enabled device. Close the gap and &ldquoSee What You Can Do&rdquo with the &ldquoPower of HART.&rdquo
| About the Author |
Ed T. Ladd, Jr., is Director of Technology Programs for the HART Communication Foundation, Austin, Texas. Upcoming articles by Ladd will provide information on applying HART technology, application notes to help you implement new HART strategies and what to expect from a HART-enabled device or host system. For more information, visit the HART Communication Foundation website.
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