1 July 2007

Computerized plant maintenance

Predictive maintenance prevents failures from happening at a bad time and fixes them before they cause damage


  • Preventive maintenance means all actions to avoid failures.
  • Enable improved uptime and reducing expenses is the point.
  • Compiling and analyzing data over time results in accurate decisions.
  • PM is worthy automation technology-for process, batch, and discrete.
By Joseph Patton

The foundation for preventive maintenance information is the equipment records.    

Somewhere, there is probably a small organization that still has records on paper, but the vast majority of equipment records should be in electronic databases. 

The benefit obtained from computerizing maintenance records is much greater than the relatively small cost. There should be a current data file for every significant piece of equipment, both fixed and movable.

The equipment database provides information for many purposes beyond predictive maintenance (PM), and includes considerations for configuration management, documentation, employee skill requirements, energy consumption, financials, new equipment design, parts requirements, procurement, safety, and warranty recovery. Essential data items include:

  • Equipment identification number
  • Equipment name
  • Equipment product/family/group/class
  • Supplier(s)
  • OEM and supplier model numbers
  • Geographic location
  • System process location
  • Criticality
  • Responsible user
  • Installation date
  • Warranty end date
  • Original comprehensive cost
  • Current value
  • Safety precautions
  • Use per day
  • Use meter reading (latest plus history)
  • PM interval(s)
  • Last PM date and meter
  • Next PM due date and meter
  • PM average time, personnel, and parts

The data for new equipment goes to the computer database immediately. The original purchase order and shipping documents can be the source, with other data elements added as they are fixed. It is important to remember there are probably three stages of configuration:

  1. As designed
  2. As built
  3. As maintained

The as-maintained database is the major challenge to keep continually current. One needs to update the master equipment data as an intuitive and real-time element of the maintenance system. If pieces of paper are used, often, they are forgotten and become obliterated with grease, and the data may not get into the single master location on the computer. 

Part number revisions are especially necessary for the rapid reordering of correct parts. A characteristic of good information systems is data should only need single entry and all related data fields will update automatically. Many maintenance applications today are web-based so one can access them from anywhere a computer (or even a personal digital assistant or enabled cell phone) can connect to the Internet.

Investment in data entry 

When the first IBM personal computer (PC) came out, it cost $8,500, and a separate 10 MB disk drive was as large as the base central-processing unit. Today, that capability would costs less than $500. 

Attitudes toward maintenance use of computers have also changed. The Information Systems departments struggled to keep strict control of all computers and software in their companies, and maintenance was usually very low on the priority list for assistance. 

Now, maintenance organizations have much greater say over what they need and how it should come. Computerized maintenance management systems (CMMS) are now commonplace.  

Internet search of just the Plant Maintenance Resource Center finds 320 different software vendors who claim to provide systems for maintenance. PM capabilities are a major element of most CMMS offerings.

Computers are only one component of the information system capability. Data entry is a challenge because big fingers often do not handle delicate electronic keypads well. Do note deciphering the handwriting of many maintenance people may be an even more difficult challenge. 

Much PM information is printed on paper since the paper is familiar and easily carried on a clipboard or stuffed into a pocket. Electronic personal digital assistants (PDAs), Blackberry two-way pagers, voice recognition, bar codes, and other technologies are coming to the maintenance teams, often with wireless communications. 

A relatively small investment in data entry technology can gain immediate reporting, faster response to discovered problems, accurate numbers gathered on the site, less travel, knowledge of what parts are in stock to repair deficiencies, and many other benefits.

Record info accurately 

All work to be done-and what actually is done-on equipment should be recorded on a work order so the data can be electronically transferred to all applicable using programs.

The ability to analyze work order data is critical to guide setting of optimum PM intervals and to detect problems related to too little or too much PM. All the metrics listed earlier can be set in the computer so they routinely undergo analysis and reporting without additional human effort.

Printed information is more useful for some PM personnel who do not easily make the transition to electronic PDAs. Laptop computers can contain all the above information for electronic viewing, but pieces of paper are often easier to carry and handle in difficult surroundings.

A major challenge is to train, coach, and discipline all PM people to record the information accurately at the time of action. A helpful technique is to show maintenance personnel how their accurate reporting results in knowledge and guidance to improve PM and other maintenance operations.

Fixed interval scheduling

Using the data entered into the equipment database for the PM intervals the computer program can quickly determine the next date or meter reading at which PM will be required. To do this, the logic algorithm divides the use per day into the PM interval. For example, a truck driven 65 miles per day divided into an interval of 7,500 miles produces an interval of 115 days. 

The program next considers the conversion between workdays and calendar days. This could be seven-fifths if Monday through Friday is the normal workweek and the truck sits idle on Saturday and Sunday. The interval would be 168 calendar days if the six holidays were included. 

The computer then converts the Gregorian calculation into Julian calendar dates so, for example, Monday, 7 June is the 159th day of 2004. Adding that 159 + the interval of 168 = 327 as the due date for the next PM. That calendar day is Monday, 22 November 2004.

Inspections and PMs based on the number of shifts are adjustable using a PM interval of shifts, and then the number of shifts per day can be one, two, or three.

It is important the inspection or PM data be easily changeable. As much as possible, it should happen automatically by the computer program. Many systems record the actual odometer reading at every fuel stop, end of shift, and other maintenance, so the meter reading is continually up to date. 

Other less often viewed equipment can have PM scheduled more on predicted dates. That meter information can be divided by the number of days to update the use per day continually, which then updates the next due date. When an inspection or PM is done and the work order closed, these data automatically revise the date last done, which again, in turn, revises the date next due.

Ability should be included in the computer program, probably through function keys or a mouse click, to display the screen view to change data and rapidly jump to the desired field, make the change, and then close the program.

Personnel should maintain transaction logs of changes to PM intervals for analysis that may indicate opportunity for improvement. The challenge here is with an interactive computer system, one can easily change data such as PM intervals, but one will not maintain or remember previous data and any trends unless the human analyst recalls past changes. Computerized data has a much better memory than the biased data a human mind will or can remember.


Equipment can "call home" 

Instruments that measure equipment characteristics are beginning to connect directly to the maintenance computer. Microprocessors and sensors allow vibration readings, pressure differentials, temperatures, and other nondestructive test data to input for analysis. 

Presently, these readings primarily activate alarm enunciators or recorders for individual analysis. There are, of course, process control systems in use today with the capability of signaling the need for more careful inspection and preventive maintenance. 

These devices are certainly cost effective for high-value equipment such as turbines and compressors. Progress is happening in this area of intelligent device management so all kinds of electrical, electronic, hydraulic, mechanical, and optical equipment can "call home" if it begins to experience deficiencies. 

Trend analysis for condition monitoring may also use computer records.

Computerized PM scheduling

The maintenance planner will normally sit down about mid-week and schedule all inspections and PMs for the following week. An HMI screen makes this easy. The planner simply enters the designation of the organization he wishes to plan for, and the ending date of the time period. That date would normally be the Saturday of the following week. 

The computer displays the PMs due, line-by-line, ranked with the highest priority (lowest number) first. The planner has the option of saying yes or no to doing that PM simply by keying a "Y" (New Line is Y by default) or "N" if the work order should not go out at this time. 

A work order will normally come up for every inspection, calibration, or PM that is to be due. The program can automatically reserve a work order number for each selected PM and will do a programmed switch to the work order screen when decisions on all jobs are final. 

The equipment and description data can automatically flow into the work order by the PM scheduling program with the information pulled from the equipment records.

Resource coordination

The maintenance planner should take the list of inspection and PM work orders to the production manager and determine when equipment can be available for the desired maintenance. 

Given those constraints, the work orders can now be dispatched for specific dates, times, and even personnel. It is often useful to schedule PM for the first job of the day since that gets the maintenance mechanic off to a good start, usually on a cold machine, without having to disrupt production in the middle of a shift.

When the work order is processing, the computer can automatically check inventory and make sure necessary parts are available in the employee's stock or at the stockroom that supports him. If parts are not available, a message should so indicate and print out a list for the stockroom of what parts are out and needed. 

The planner should have the ability to override the computer program edits and to decide to do the PM even though the parts are not available. If the parts are available, they should print straight to the work order copy that will go to the employee and also on either a copy of that same work order or a separate pick list that prints for the stockroom.

If the stockroom has its own printer, then the pick list can print there. At the same time, the computer should transfer those PM parts from the "on hand" inventory to "on reserve," linked to that specific work order. When the maintenance person picks up the parts, a computer program should transfer the parts from "on reserve" to that specific work order. 

Then finally, when the work is complete, the parts transfer to the specific equipment of which they are soon to be a part. Necessary cost accounting happens at the same time. Unfortunately, not all work happens on time, so an electronic monitor or paper report is necessary. 

Capabilities should be in the programming to indicate any other active work orders that should happen at the same time. Modifications, for example, can wait until other necessary work so everything can happen at once for efficiency's sake. 

A variation on the same theme is to ensure emergency work orders will check to see if any preventive maintenance work orders might also happen simultaneously. Accomplishing all work at one period of downtime is usually more effective than doing smaller tasks on several occasions.

Preventive maintenance procedures may be stored in the computer and printed at the same time as when the work order goes out. Most computers have standard software for word processing capability so one can enter and revise procedures. 

While paperwork from a computer system should be at a minimum, a printed procedure checklist the inspector can sign helps assure responsible accomplishment of the tasks. Single-point control over procedures is a big help, especially on critical equipment. The risk of pulling an obsolete procedure from someone's file drawer is less. 

If all items on a procedure cannot happen on one shift, the document can pass along to the next shift supervisor or sit for action the following day. When completed, the work order would close out, and related information is entered automatically onto history records for later analysis.

Safety inspections and legally required checks can stay in the computer records for most organizations without any need to retain paper copies. If those paper records must, for some legal reason, be in hardcopy, then they should be in microfilm form or as electronic images rather than in bulky paper form.

Humans are still more effective than computers at tasks, which are complex and aren't repetitive. Computers are a major assist to humans when tasks require accurate historical information and which happen over and over. Computer power and intelligent software greatly enhance the ability to accurately plan, schedule, and control PMs.


Joseph D. Patton, Jr. (jDPatton@PattonConsultants.com) is an ISA Life Senior and CEO of Patton Consultants. He is a registered PE. His book, Preventive Maintenance, is a source for this feature article.