Analog+HART I/O

Improving batch process efficiency with dramatic cost savings
through the use of HART protocol-enable I/O.

HART protocol originated in the late 1980s and remains a key tool for improving plant operations.  Traditional applications of the protocol have included plant asset management, commissioning and periodic maintenance activities.  Control applications were typically limited to large-scale distributed control systems.  This was primarily due to the fact that integrating HART data into the control system required a separate HART data collection system that was run in tandem with the primary analog acquisition system.  Implementation of these systems can be costly due to the additional hardware and cabling requirements.

 An emerging industry trend is the integration of HART capability into the analog acquisition system.  This eliminates the need for external hardware and provides full access to HART data via the control system network.  Integrated HART I/O for programmable controllers is a logical evolution of the technology.  Spectrum Controls has recently introduced a pair of I/O modules for the Allen-Bradley ControlLogix PLC that incorporate analog input and output capability as well as the ability to read and write HART data to field instruments over the existing wiring system.

Kraft Foods (Beaver Dam, WI) has been using HART protocol-enabled instrumentation for 6 years.  “We have used HART primarily for maintenance and commissioning of our systems” says Steven Stippich, Plant Engineer.  Normally, Kraft only had access to this data if it was deemed critical.   Kraft would then implement a multiplexer system and interface it to the PLC using a communications adapter.   “HART I/O provides a seamless interface to our HART enabled instruments when compared to other PLC interface solutions.”

The cost savings associated with HART I/O is dramatic.  A typical multiplexer installation requires additional wiring and panel space to accommodate the connections to the multiplexer and the bridge wiring between the multiplexer and the analog I/O.  A communications bridge module is necessary to tie the multiplexer data into the PLC backplane.   Steven indicates: “Installation is as simple as installing a standard analog module. It does not require extra panel space or wiring,” says Stippich.   The overall savings per HART I/O point is over 600% and similar to standard analog acquisition costs.

Kraft’s first implementation of this technology was used to measuring the volume before and after a solids separation system in their dairy processing facility.  This is similar to a large centrifuge.  The system includes Spectrum Controls’ HART-enabled analog I/O modules for the Allen-Bradley ControlLogix PLC.  The I/O is interfaced to an Endress + Hauser Promass 63 mass flow meter.

 The I/O measures the traditional analog current loop value and polls the flow meter, using HART communications, and provides variables including flow rate, density, temperature and totalized volume.   These measurements can then be used to calculate the efficiency of the separator.

 An added benefit to the system is that the HART data is now available to the operator from their workstation via the PLC’s Ethernet network.  Plant Asset Management software can monitor device health and troubleshooting may be performed real-time without leaving the operator workstation.  HART-enabled I/O has allowed Kraft a simple, cost-effective and flexible solution to control and monitor their processes