Asset management software (AMS) has become more powerful than ever for improving predictive, condition-based, or reliability-centered maintenance. It can also extend the reach of computerized maintenance management systems (CMMS). The latest packages can analyze fluctuations and trends, alerting operators to problems before they happen.

But even the best AMS will be worthless without the accurate, real-time data provided by smart instruments. This article examines recent developments in instrumentation, as well as HART and fieldbus interfaces that can help you get the most from today's AMS programs.

As smart instruments and AMS continue to transform plant maintenance, the days of reactive maintenance programs are clearly numbered. Even preventive maintenance, where work is performed whether it's needed or not, is proving to be wasteful.

According to recent studies by Fisher Controls and Honeywell, up to 75 percent of valve repairs are unnecessary. At $2,000 to $3,000 per valve, per year, that's a lot of drain for any large manufacturing plant.

Preventive maintenance (PM) sometimes causes problems because it can introduce infant mortality into what was once a perfectly functioning device. In other words, it was working fine until you fixed it.

Reactive maintenance is worse. When a system fails, it often takes the process down with it. Maintenance personnel have to scurry to fix or replace a flowmeter, valve, pump, or loop controller. Meanwhile, operations people and plant management stand around, watch the clock, frown at the revenue being lost every minute the line is down and think dark thoughts about the competence of their maintenance crew.

It should come as no surprise that the hot topics among maintenance folk today are RCM, predictive maintenance and condition-based maintenance. Today's AMS programs enlist smart field instrumentation, sensors, diagnostic instruments and software to detect small problems before they become big problems.

The theory behind all this new technology is that most field devicesmotors, valves, pumps, flowmeters and so oncan provide some warning that a failure is imminent. Motors draw too much power, actuators use too much air, valves stick, pumps vibrate and flowmeters clog. Smart instruments can detect the symptoms.

Here's a perfect example: "One of my clients has several hydrolyzers that operate at 535 F at about 905 psig," says John Ross, control engineer for Lockwood Greene Engineers, an E&C firm in Spartanburg, S.C. "The bottom products, water and glycerin, are let down with a single control valve which, as you might expect, takes a beating. The valves would often fail catastrophically even though they were being totally rebuilt during annual scheduled shutdowns."

Ross is describing a typical PM scenario, where valves are rebuilt whether they need it or not, and then fail anyway. "I recommended the company install 'smart' positioners, and log the performance data sent back on HART. They are now able to predict an impending failure and switch valves before the suspect valve body is damaged."

This practice is transforming the face of maintenance: using smart instruments to gather data about equipment, feeding that data to maintenance software that can find pending problems and fixing systems before they break.

You may already have hundreds of smart instruments in your plant. HART has been around for 10 years, and nearly every valve, positioner, flowmeter and 4-20 mA transmitter you've installed since then probably has a HART interface. If you have commissioned a field instrument with a handheld device, you probably used a HART programmer. In that case, you already have much of what you need to do condition-based maintenance.

Wade Howarth, automation manager at Cargill Health and Food Technologies, Eddyville, Iowa, has 3,000 instruments at his plant, and 1,500 of them have HART interfaces. "We installed an AMS from Emerson Process Management, and immediately discovered problems on 30 valves," says Howarth. "Problems included air leaks, crimped air lines, feedback linkages and liquids in the termination blocks. We found out why we had such excessive nitrogen costs."

In case you are not familiar with HART, here's a quick summary: a HART transmitter imposes a digital signal on its 4-20 mA process output. The digital signal contains a host of information about the field device, such as status, alarms, signal strength, diagnostic information and data quality. Devices such as valve positioners can provide data related to valve hunting, stiction and wear.

Gaining access to the information contained in a HART device is easy. If you have a modern process control system (i.e. one that was installed in the past 10 years) it may already have HART software. If not, the vendor probably has it by now, and you can install it. The vendor probably also has the software you'll need to analyze the HART data and look for problems.

If your control vendor can't help, you can still obtain the information easily. Because the digital information is riding on the 4-20 mA signal, you can extract it with a HART modem or multiplexer, and read it into any PC. Hardware and software for using HART information is readily availablesee www.hartcomm.org for more information.

Fieldbus is not as widely used as HART, but it is coming on strong, particularly in new plants. Fieldbus can be considerably more expensive than HART, but it has more capabilities, particularly in equipment diagnostics.