The three types of preventive maintenance

“Preventive maintenance” gets used as if it were a single thing, but it’s actually three distinct mechanisms that respond to three different ways equipment wears out. Picking the wrong one for a given piece of equipment is the most common cause of two opposite problems that coexist in almost every facility: over-maintained machines, and machines that break down between inspections.

Here’s what the three are, when to use each, and how to set them up.

1. Time-based

The classic: every three months, every year. It’s the easiest to plan and the easiest to audit, because the calendar is an objective fact.

When it makes sense. When deterioration happens whether or not the equipment is in use: rust and corrosion, aging of gaskets and elastomers, degradation of oils and lubricants, consumables expiring, and anything a standard or the manufacturer specifies in months.

How to set it up. The checklist template is linked to the asset, its model, or an entire family, and you define the frequency in days or months. From there preventive maintenance generates the work orders on its own, with technician and date assigned, checking beforehand whether the day is a holiday and whether that person is available.

A single asset can have several periods at once, each with its own record of when it was last carried out: the monthly check is one thing and the annual one with component replacement is another, and neither replaces the other.

Its limit. It treats equipment that works very differently the same way. Two identical machines installed on the same day can have very different service hours, and the calendar doesn’t know that.

2. Meter-based

Here the trigger isn’t the date: it’s accumulated use.

When it makes sense. When wear depends on how much the equipment works: mileage on a fleet, running hours on a motor or compressor, cycles on an automatic door or an autoclave, units produced on a line.

How it works. The asset carries a counter with its unit. You define a limit — the units that maintenance task or component is expected to last — and a warning percentage.

When a technician logs a reading, the system adds it to the accumulated total, calculates what percentage of the limit has been consumed and, if it crosses the threshold, automatically generates the preventive work order, with its asset, its location, and the checklist template that matches that equipment.

Its limit. It depends on someone taking the reading. If the counter is read once a year, the alert arrives a year late. That’s why it’s usually combined with a reading round scheduled by time: time-based preventive maintenance goes and measures, and the measurement triggers meter-based preventive maintenance.

3. Condition-based

What most people call predictive. You intervene when a measurement indicates the equipment is degrading, not when the calendar says so and not when it has already failed.

When it makes sense. On critical equipment whose failure gives warning: vibration in rotating machinery, temperature at connections and bearings, electrical consumption, oil analysis, differential pressure across filters.

How to get started, and this is the important part. You don’t need sensors. Checklists support fields with a minimum and maximum value, so a reading outside range gets logged as an anomaly on the spot. A monthly round with a thermometer and a portable meter already produces a time series, and a time series lets you see a trend.

Continuous sensing speeds that up; it doesn’t create it.

Its two real requirements. First, the baseline: the threshold doesn’t come from a catalog, it comes from how that piece of equipment behaves at that facility, so you have to start by measuring equipment that’s working well. Second, the anomaly has to turn into an incident with an owner and a date; if it gets logged and nothing happens, the technician stops logging it.

There’s more detail in predictive maintenance: how to get started.

How to choose for each piece of equipment

The question that settles it almost every time: what does this equipment’s deterioration depend on?

It depends on…	Mechanism
The passage of time	Time-based
How much it works	Meter-based
Its condition, and it warns before failing	Condition-based
A standard or the manufacturer	Time-based, at the frequency they set

Normally you combine them. A compressor might have an annual time-based check — gaskets and oil — a filter change by running hours, and vibration monitoring by condition. All three coexist on the same asset.

A fourth trigger that isn’t technical

There’s one variable that decides more money than vibration ever will: how much you’ve already spent repairing that machine.

You can log an asset’s replacement cost and a warning percentage, and the system notifies you when accumulated repair spending crosses it. It doesn’t generate a work order — replacing a piece of equipment is a business decision, not a task — but it puts the number in front of you right when it’s time to look at it.

What makes any of the three actually work

Configuring by family. Checklists resolve in a cascade — asset, model, subfamily, family — so two hundred identical machines get configured once.

Recording it in the field. The app works without coverage and queues up actions, because maintenance happens in basements and machine rooms. If the technician writes it down on paper, the values come out rounded and the series loses precision exactly where it matters.

Reviewing the plan. With the history in front of you, the reports show which equipment fails between checks — raise the frequency — and which has gone several cycles without a single anomaly — probably has too many visits. Both situations cost money.

If there’s a regulatory obligation

Worth knowing before you go looking for it in the menu: legally required maintenance isn’t a module. It’s done with the time-based mechanism, linking the checklist a standard requires and its frequency, and the proof comes from the order history, the completed checklists, and the documentation with its dates.

The software records and demonstrates; the company is the one that complies with the standard.

Where to start

With the critical assets, deciding for each one which of the three mechanisms applies. It’s an afternoon’s conversation with whoever knows the equipment, and it’s the one that most determines whether the plan is going to work.

If you want to see it set up on your own equipment, you can request a demo.