Louis F. Szabo, Meriam Process TechnologiesWhat’s the difference between using an RTD sensor to measure temperature and a thermocouple? One plant found out the answer was $2 million. That was the fine imposed by the U.S. Food and Drug Administration after a plant inspection.
An RTD transmitter had been substituted for a thermocouple transmitter during plant commissioning because of its better accuracy and linearity over the expected temperature range. But that change was not documented per 21 CFR, the FDA’s guidelines for electronic records change management. The FDA caught the error and imposed the stiff fine on the manufacturer for that one instance. What can be done to prevent another expensive error such as this? With 4-20 mA field devices that are HART-enabled, the plant commissioning phase is quite different. In HART devices, the 4-20 mA analog channel is supplemented by a digital channel supporting read/write access of all device data. With HART-enabled control software, field devices are configured and calibrated after installation, which minimizes errors and commissioning time, and everything is documented to comply with FDA guidelines.
The Power of HARTReducing the commissioning time contributes to determining the return on investment for a plant. Plant operations and maintenance are also affected by the abundance of data available in every HART device. Minimizing installation, operations and maintenance costs can often justify the added capital expense of a fully-integrated HART plant in less than one year. Other key benefits in HART device and control systems include:
HART systems are simple, high-value, low-risk propositions that are easy to use and maintain.
HART systems have the ability to keep accurate records that meet the compliance and traceability requirements of the FDA and OSHA. HART systems diagnose problems in real-time and can predict maintenance cycles based on valve closures, for example, rather than those based on the calendar.HART systems can be used to optimize raw material consumption. For instance, if raw material spot pricing is high, the cost of producing a product is elevated. By keeping tighter control of raw material consumption, the product cost is optimized. HART systems can monitor faulty equipment. HART diagnostic information is returned with every message. For critical devices or safety devices, if the diagnostic information indicates a problem, action can be taken automatically or manually. For instance, a device returning a diagnostic bit can be monitored at a higher rate to gather trending information, or linked to annunciators, recorders or predictive maintenance algorithms.
In batch operations, HART systems can rescale field devices remotely as recipes change. The HART device even confirms the change to the host system to ensure a closed loop quality control system. This feature is lacking in conventional and proprietary systems. Integration of HART field devices with existing plant control, safety, and asset management software leads to increased productivity while lowering maintenance costs.
Making a Move to HART
Let us look at the popularity of the various types of field devices. According to the ARC Advisory Group (Dedham, MA) and shown in Figure 1, the worldwide installed base is 40-45 million devices. Approximately one-half are analog devices and another one-fourth are HART devices.
So, there is a pre-existing knowledge base among operator and maintenance personnel when upgrading 4-20 mA devices to add HART capability, at no additional cost. And the hardware and software tools used to communicate with HART devices, such as a handheld calibrator or plant asset management software, are designed for plant technicians and engineers.
But there is one overwhelming reason to consider HART for plant retrofits or expansions: the investment in copper wiring. Using a rule-of-thumb of $1 per foot of already installed copper wiring in conduit, and assuming 5000 devices at an average distance of 300 feet, the investment in wiring is $1.5 million. With those same wires used for analog control, you can have read/write access to all HART device data over the existing infrastructure.
Start in the Field
Implementing a HART strategy starts with the field devices. You must identify the critical areas in the process and decide whether to layer a HART communication channel over the analog channel, or combine a HART bus with other field buses. In a system consisting of thousands of devices, a relative few will be deemed critical. The rest are for monitoring the process, but are not critical. The critical devices are necessary for controlling the product quality and should have higher reliability and, potentially, accuracy. In the last five years, a SIL (safety integrity level) rating is available for process devices. In general, a higher the SIL rating leads to increased reliability for a given device. These devices may also have a higher level of diagnostics. As a result, more information regarding the health of such devices is available, but only if it is monitored.
You probably already have an inventory of field devices. Which are HART-capable or could be retrofit with HART devices? After making those determinations, identify what HART information is available and what advantages having that information can bring. It might be among the 35-40 data items in every HART device, like the serial number, calibration date, secondary measurement values, or error conditions. Or it might be a device-dependent variable, like the totalizer values in a flow meter that could be cleared between batches.
At the same time, identify which measurement functions could be combined into one device. There are HART devices with the capability, for example, of measuring temperature and pressure. This reduction in the number of field devices has initial and continuing costs savings.
Getting the Data
Having HART device data available in the field is advantageous for technicians with handheld calibrators and communicators, but bringing that data into the control room gives operators the ability to monitor and maintain alarm conditions and malfunctions. The data is also useful when creating maintenance schedules with audit trails for the devices. With integration to the control room, trips to the field and their associated costs are minimized.
There are two methods to acquire HART data from field devices: a HART multiplexer and host combination that monitors hundreds of devices, and a HART I/O module that combines an analog I/O module with a HART interface. HART’s digital communication is intended for process control. The digital signal can be slow, especially when used with old multiplexers. Where fast response times are necessary, the analog signal is used to read measurement values. Higher-speed digital buses are necessary for machinery control and in PLC applications that require millisecond response times.
Making Use of the Data
Accumulating, storing, and accessing the data of field devices require an application server running a database program known as device life-cycle management software. The program manages and documents device configurations and calibrations. Here are some key features to look for when evaluating this type of software:
Support for the complete life-cycle, from installation and commissioning, to startup and operations, to maintenance and repair.
Support for all HART or conventional field devices so you can continue to purchase the best devices, regardless of manufacturer.p>The ability to track, record and maintain all activity with field devices, so you have an audit trail for corporate and agency compliance.
Support for open standards like SQL for accessing database information and OPC for exchanging process control data.
Integration with a maintenance, repair and overhaul (MRO) system to schedule work, needed resources, and paperwork such as work orders.
Integration with handheld calibrators and communicators to eliminate “clipboard” commissioning and maintenance. This can reduce labor costs by as much as 50%.Of course, the software should have the ability to grow as your plant adds product lines and as manufacturers introduce new field devices.
Getting the System Up and Running
In a plant with device life-cycle management software, HART devices are installed in an unconfigured or preconfigured state. An unconfigured state minimizes human errors for installations. Once communication is established, non-configurable data, like serial number and firmware revision, are uploaded from the devices, and user-configurable data, like zero and span, are downloaded to the devices. Preconfigured devices must be validated prior to commissioning the system. The configuration is compared with the configuration data specified by the engineers and documented.
This streamlined installation procedure is especially useful when duplicating a production line. The line can be duplicated right down to the device configurations, and that data can be downloaded to the field devices. This can cut the commissioning time in half.Because the configuration of HART devices is extremely flexible to allow for the best fit, they are complex to configure. The ultimate configuration of options needs a close review to ensure the devices will handle operating conditions properly and fail conditions predictably.
There is an 80/20 rule in a plant’s startup and continuing costs over its lifetime: 80% of the total costs are associated with operations and maintenance, and 20% of the total costs are associated with installation and commissioning. The benefits of integrating HART field devices with device life-cycle management software are even more apparent over the life of the plant.
The greatest impact is less labor for the repetitive tasks of configuration and calibration checks. These can be performed remotely from the control room or maintenance shop and may not require a visit to the field device, which may be in a difficult to reach or hazardous location.,
Maintenance schedules become more predictive as device life-cycle management software tracks historical data of the devices. Examining trends of equipment performance and scheduling repairs before a problem occurs leads to less downtime. But it is necessary to change the maintenance mindset from being driven by the calendar to being driven by device information. Analyzing the data takes training of operators and technicians, plus a commitment by management to follow through the preventive or predictive maintenance needed.
Troubleshooting problems can be done remotely. When a device requires field troubleshooting by a technician, they will have performed remote diagnostics already. And when a device needs replacement, its configuration can be cloned into a new one. Many field devices are installed for years. Device replacement from stored configurations appears straightforward. However, devices having the same model numbers from the 1990s and today have different firmware as HART has evolved from Revision 4 through Revision 6, and manufacturers have added features and capabilities. As a result, the old configuration will result in a “device mismatch” with the new device. Meriam Process Technologies has an automap feature with field device revision independence that automatically maps the old configuration to the new device. The user maintains the ability to update devices, but downtime is minimized.
Automapping extends to replacing conventional field devices with intelligent ones, and replacing one manufacturer’s device with a similar device from another manufacturer, especially important for device failures and unexpected shutdowns.
To comply with the FDA’s guidelines for electronic records and electronic signatures, referred to as 21 CFR Part 11, pharmaceutical plants must document the initial configuration of field devices, and track and document subsequent configuration changes. If you do not have an audit trail of changes and inspectors find you in non-compliance, you will be subject to stiff fines.
Compliance to the FDA guidelines can be accomplished with device life-cycle management software. It is an enabling technology that provides the necessary documentation and security for 21 CFR Part 11. It issues birth certificates when devices are put online, and issues death certificates when devices are retired. The audit trail lists all changes in configuration and calibration to field devices. There are levels of security that are password protected, so that only qualified and authorized technicians work on devices. Password protection also ensures authenticity of signatures for calibration signoff.
Technicians use handheld terminals to calibrate and configure HART field devices. Compliance with 21 CFR Part 11 is coordinated by the device life-cycle management software. Once the handheld terminal is registered with the software, scheduled MRO tasks are downloaded to it.
Figure 2 outlines the next steps taken with handheld terminals in the field. In this case, a user login, procedure signoff, and checker signoff are shown. In addition to calibration changes, any necessary configuration changes are recorded by the handheld terminal. After all tasks are performed, electronic records and signatures are logged into the device management software. A history of each device, from birth to death, is compiled for further review and audit.
Full Integration into Plant
There is a wealth of information about plant operations in the database created by device management software. Sharing that information with an MRO system has already been discussed, but that is only the beginning. Figure 3 shows how a common database with open standards can link all the software tools of the plant, integrating operations and maintenance with enterprise tools. This leads to efficiencies for data backup and device ordering, for example.
The various software tools and efficiencies are described as:
Device management system – Configures and calibrates field devices. Tracks and documents changes.
Valve management – Software that exercises valves, tracks closures, and gets valve signatures.
Plant automation system – The actual control system. Acts as supervisor, watches for device failures and error flags.
MRO software – Communicates with business management software, issues work orders and purchase orders.
Engineering tools – Software used by engineers to design control systems. HMI (human-machine interface) – Operator interface to the monitoring and control software.
Batch historian – Keeps recipes constant and tracks changes.
Integrating HART device management software into the enterprise realizes benefits for plant operators, technicians, engineers, and managers. In a fully integrated HART plant, operators communicate with field devices to upload and download parameters and commission devices, technicians communicate with field devices for calibration and troubleshooting, either remotely or locally, and all of this is documented for company policy, government agencies, and legal requirements. HART integration pays for itself with productivity gains, maintenance savings, and avoiding fines for non-compliance.