Process Instrumentation Diagnostics & Communication Interfaces

There are various technologies that are available that help plant automation personnel to obtain diagnostic data which inform the type of maintenance to be undertaken. For example, using Distributed Control System (DCS), PC software tools, or handheld communicators, plant automation professionals can diagnose the health of an instrumentation device while it is in the line. Digital controllers incorporate preset system mechanisms for maintenance diagnostic to provide alerts if there are problems with instruments, electronics and hardware as well as valve performances. In this article we look some of the key tools or software used in plant for process diagnostics as well as for communication interfaces.

HART Technology

HART which is an acronym standing for Highway Addressable Remote Transmitter is a standard way in which instruments digitally communicate with one another over the same two wires used to convey 4-20 mA analog instrument signal. To put it in another way, HART is a hybrid communication standard, with one variable (channel) of information communicated by the analog value of a 4-20 mA DC signal and another channel for digital communication whereby several other variables could be communicated using pulses of current to represent binary bit values of 0 and 1. Those digital current pulses are superimposed upon the analog DC current signals, such that the same two wires carry both analog and digital data simultaneously.

A HART-enabled transmitter is able to send and receive digital data as AC signals (current pulses in sending mode, voltage pulses in receiving mode) superimposed on the same two wires carrying the 4-20 mA analog signal and DC power. A computer device equipped with a HART modem, the required configuration software and an appropriate device description for that specific instrument may communicate with the HART transmitter if connected in parallel with the transmitter’s loop power terminals. A typical connection would look like the one below:

Alternatively HART-based handheld field communicators can be used instead of a PC. HART communicators are battery-powered, portable devices specifically for configuring HART-enabled field instruments. Like PC, they need to be updated with device description files to be able to communicate with the latest models of HART-enabled field instruments.

With HART technology you can access the following features:

• Diagnostic data may be transmitted by the field device (self-test results, out-of-limit alarms, preventing maintenance alerts, and so forth).
• Field instruments may be re-ranged remotely through the use of HART communicators.
• Plant technicians may use HART communicators to force field instruments into different mode (manual) for diagnostic purposes like forcing a transmitter to output a fixed current so as to check calibration of other loop components, manually stroking a valve equipped with a HART-capable positioner.
• Field instruments may be programmed with identification data such as tag numbers corresponding to plant-wide instrument loop documentation.
• You can diagnose the health of a valve remotely via HART, which enable predictive maintenance without disrupting the process.
• Lastly, HART-based handheld field communicator when connected to the digital valve controllers enables user-configured alerts and alarms, providing notification of current status and potential valve and instrument problems, including travel deviation, travel limit and cycle count accumulation.

Related article: Features of HART Communication Protocol

AMS Device Manager

This platform allows easy access to powerful device diagnostics for configuration, calibration and documentation of the operating characteristics of HART and Foundation Fieldbus FIELDVUE digital valves.

ValveLink Software

This is a software package that communicates with HART and Foundation Fieldbus FIELDVUE Digital valve controllers. Using this software, instrument engineers, maintenance technicians or operators can fix problems before they affect the process.

ValveLink Software enables the evaluation of control valves while they are fully operationally before failure without disrupting the process.

With this ValveLink Software, you can remotely configure and monitor valves as well as monitor the valve performance and health in real-time.

ValveLink SNAP-ON provides integration with AMS Device Manager to perform tasks. Integration with AMS Device Manager provides the ability to communicate with FIELDVUE digital valve positioner via DeltaV, HART multiplexers, HART Modems, PROVOX, etc.

DeltaV DCS

A Delta V Distributed Control System (DCS) is a control system developed to protect and enhance the plant performance. The safety integrity is provided by continuously monitoring sensors, logic solvers and final elements, with faults diagnosed before they cause process failures. In other words, it is an automation system built to simplify the operation complexity and lower the project risk.

FIELDVUE Instruments

Plant personnel utilizing FIELDVUE performance diagnostics, can monitor valve operation online/remotely to evaluate the performance and reliability.

Valve Type & Characterization Devices

These are electronic devices that attempt to produce valve characterization by electronically shaping the I/P positioner input signal ahead of the positioner to recalibrate the input 4-20 mA signal, utilizing a pre-programmed table to produce the desired valve characteristics

You may also read:

• NAMUR NE 107 Standard for Modern Instrumentation Diagnostics
• Electro-Pneumatic Valve Positioners: Function & Features
• Volume Booster: Function, Operation & Application
• Valve Positioners: Function & Types
• Programmable Automation Controllers (PACs) – Features & Applications
• How Controllers are used in Industrial Automation Systems