Acondition monitoring program collects data from a machine while it’s operating and detects changes in the machine that may cause a component to fail. By flagging problems at an early stage, the program tells the user when to perform maintenance, thus preventing unexpected shutdowns. Such programs cut downtime and parts inventory, boost productivity, improve quality, and ultimately, increase profits.

Before attempting to start a condition monitoring program in your plant, identify what you want to achieve, such as increase machine uptime, prevent failure of machines that are crucial to a major operation, protect workers from the consequences of machine failure, and enhance product quality.

Then conduct a comprehensive survey of your equipment. Review the operating characteristics and repair history of all machinery in your plant, including production and maintenance records.

If you have several similar machines, check the nameplate data on each one. Its components may have been replaced without updating the machine drawings or records. Document the equipment as it exists — not as it was originally installed.

Next, review each machine’s function and duty cycle, plus its probability of failure and the consequences of an unexpected shutdown. This will give a good indication of the type of monitoring required — either periodic or continuous.

Periodic monitoring. Machines that perform secondary or support-type functions generally require only periodic data collection. Examples include slurry pumps in cement plants, condensate pumps in power plants, and auxiliary fans. These devices are usually small (less than 50 hp) and often perform redundant functions. For example, when several pumps perform the same function, one can shut down while others continue to operate, or a standby unit replaces the failed one.

Periodic monitoring is usually adequate for machines that operate reliably or give advance signs of deterioration. The interval between measurements depends on the machine’s failure history. For example, a machine that normally breaks down within minutes after the first sign of trouble needs more frequent measurements than one that takes several hours or even days.

For this type of application, choose a simple vibration detecting pen or a handheld data collector with diagnostic functions (cost $800 to $10,000). An operator can easily take such a device almost anywhere in a plant.

Though the equipment cost for periodic monitoring is relatively low, the ongoing cost can be high (depending on the number of monitoring points and measurement frequency) because this method is labor-intensive.

Hand-held devices are not advisable in some cases, either because monitoring points are inaccessible (50 ft off the ground in a grain elevator) or in dangerous areas (near exposed rotating equipment or in toxic environments). For such cases, a better choice may be a simple online data acquisition system that monitors data periodically. Such systems cost $500 to $1,000 per measurement point.

Continuous monitoring. Prime candidates for continuous monitoring include machines that run 24 hours a day, perform functions that are crucial to a major operation, have high failure consequences, are expensive to maintain, or could pose a risk to personnel safety. Examples include machines used in continuous processes, such as paper manufacturing or chemical processing, where a service interruption could ruin an entire production run. Those with high failure consequences include power plant boilers, turbine generators, and equipment located in hazardous environments. Also consider machines that experience frequent failures because of a tough operating environment — common in mines, cement plants, and fertilizer plants.

If it’s absolutely necessary to prevent a machine from breaking down, select a device that continuously collects machine data such as vibration, temperature, and flow, then compares the data to alarm criteria and alerts the operator (to take corrective action) if any data reaches these criteria. Here, the cost can range up to $1,500 per measurement point.

Continuous monitoring requires a larger investment for on-line data acquisition and analysis equipment plus installation. Once a continuous monitoring system has been installed, however, the on-going cost is relatively low because the system functions automatically with little or no operator assistance.

Monitoring multiple parameters

With either type of data collection — periodic or continuous — the best way to ensure trouble-free machine operation is to integrate the measurement of several machine parameters in the monitoring system. For example, a complex paper-making machine may require measuring motor temperature, bearing temperature and vibration, and gearbox vibration — all at various points within the machine. Such an integrated approach increases the probability of detecting a malfunction at an early stage, so operators can diagnose the problem, prescribe an operational or maintenance cure, and perform the required correction before a failure occurs.

One company, KNP Paper in the Netherlands, keeps track of bearing and gear conditions in a large paper-making machine that operates 24 hr/day, Figure 1. In this machine, moisture-laden paper passes over a series of rolls that gradually reduce its water content. Roll size and temperatures vary within three main sections of the machine, as do bearing loads and speeds. Therefore, the company installed accelerometers and thermocouples to monitor vibration and temperature at several key points in each section. All sensors are linked to a computer that analyzes the data and detects conditions such as imbalance, misalignment, and bearing and gear defects. Identifying such defects at an early stage lets the company schedule timely maintenance and avoid unexpected shutdowns.

Outside help

Many companies don’t have the expertise or the resources to start a condition monitoring program alone. If internal resources are limited, or you’re uncertain where to begin, call on an outside source for help — either a manufacturer of condition monitoring equipment, an independent consultant, or a supplier of remote condition monitoring services. These sources offer services such as analyzing your needs and making system recommendations, preparing a cost-benefit analysis, training, and even implementing a monitoring program.

It’s important, though, to establish your goals and budget for the program before you call in an outside expert, and to communicate these clearly. By doing so, you’re more likely to achieve the expected benefits while preventing misunderstandings.

To find a good outside source, remember that experience is the key. Choose a company that:

• Takes a comprehensive approach to condition monitoring.
• Is knowledgeable about current technology in monitoring equipment.
• Is familiar with the type of machinery and plant processes used in your industry and is able to tailor a program to your particular needs.

Carefully evaluating the company’s success rate, references, and reputation will help ensure that you choose the right one for the job. Ultimately, the company’s experience and capabilities are more important than the type of company or its size.

Monitoring equipment manufacturers. Companies that manufacture condition monitoring equipment are usually a good source of information and assistance, especially if you’re just starting a program.