Do micro-stops count as downtime?

Micro-stops are downtime: the machine stopped, and every minute of it costs output. Standard OEE definitions book them as a performance loss instead of an availability loss, because reasons are logged only for stops longer than a cutoff of a few minutes. The cutoff moves the loss from one factor to the other, and OEE stays the same either way.

Operators shouldn’t classify a 30-second stop; a rule should. This guide, for plant managers and the operators who classify stops, works one shift both ways, sets the cutoff from a week of stops and covers the settings that decide which stops anyone sees.

What is a micro-stop?#

Vorne’s OEE primer lists the usual causes: misfeeds, material jams, obstructed product flow, incorrect settings, misaligned or blocked sensors and periodic quick cleaning.^[1] It also notes that most companies don’t track these stops accurately, and that the underlying problems are often chronic: same problem, different day.^[1]

A micro-stop is still a stop. The machine record counts it in full whether or not anyone gives it a reason, as the glossary entry for downtime puts it.

Where the line sits#

No standard fixes the duration. Each plant draws its own line, and published sources differ by more than a factor of seven.

The line matters more than its exact value. In that bottling study, micro downtime under 15 minutes covered 57% of the inefficiency on the least efficient line the authors analyzed.^[3] Short stops are rarely a rounding error.

Do micro-stops count as downtime?#

Yes, on the machine’s record. A machine that sits still for 40 seconds produced nothing for 40 seconds. The open question is which bucket of your OEE calculation that time lands in, and that depends on how you book it.

You have two choices:

• Book it as downtime. The stop counts against availability. A rule gives it one reason, such as Short downtime, so nobody has to.
• Book it as running time. The stop never reaches the downtime record. The parts it cost still go missing, so the loss shows up in performance instead.

Vorne’s definitions follow the second choice. Availability covers stops long enough that a reason is worth tracking, and performance covers slow cycles and small stops.^[2] Vorne lists idling and minor stops as one of the six big losses, and as a performance loss.^[1]

What is OEE? maps all six losses to their factors.

Where micro-stops show up in OEE#

The cutoff decides which factor carries a micro-stop. It never decides whether the loss counts. OEE reduces to good output measured in ideal time over planned time:^[2]

Run time appears nowhere in that formula. Moving a stop from running time to downtime lowers availability and raises performance by exactly the same factor.

The number holds, but the story changes. Under the first booking, a supervisor reads 84.6% performance and concludes the line runs slow. It doesn’t: it runs at 95% of rated speed between 90 interruptions.

A stop record lets you split the performance loss. The 20,805 cartons are 346.75 minutes of output at 1 second each, so performance lost 410 − 346.75 = 63.25 minutes under the first booking.

Of those, 45 are micro-stops and 18.25 are slow cycles. A faster speed setting recovers the 18.25; it does nothing for the 45. Those 45 minutes are 2,700 cartons at the rated speed.

Should operators classify a 30-second stop?#

No. A 30-second stop has a cause, but asking the operator for it every time costs more than the answer is worth. In the cartoner shift, 92 stops would each ask for a reason: one about every five minutes, mostly from the person who cleared the jam seconds ago.

Classify by duration instead. Auto-classification is a rule that puts a reason on a stop without anyone choosing it; the glossary defines auto-classification the way IoTFlows uses it. With a short-stop rule, the operator in that shift explains two stops, and the rule labels 90.

You still need the causes of micro-stops. Get them by studying one machine for one shift, not by asking about every stop on every machine. Reduce micro-stops covers the study. The reason-code guide’s starter list shows which codes a rule assigns and which an operator picks.

How do you set the short-stop cutoff?#

Set it from a week of real stops, not from a number someone quotes. Stop durations on most machines split into two groups: a large pile of short, routine stops and a thinner spread of longer ones. The cutoff belongs where the pile ends.

1. Record every stop for a week

   Use a machine signal, not a log sheet, so stops of a few seconds are in the data. One week covers each shift and the usual product mix.

2. Count the stops by length

   Bucket them: under 30 seconds, 30 to 60 seconds, 1 to 2 minutes, 2 to 5, 5 to 15 and over 15. Count stops, not minutes, because the cutoff is about how many questions you ask.

3. Find where the count drops

   In the case packer week, 450 of 478 stops are under 2 minutes, and only 14 fall between 2 and 5. The drop at 2 minutes is the edge of routine jam-clearing.

4. Set the cutoff at the drop

   Put the cutoff where routine stops end. Every stop under it gets one automatic reason, and every stop over it asks the operator.

5. Check the cutoff after a month

   If operators still classify dozens of stops a shift, the cutoff sits inside the pile. If the short-stop code’s total climbs on one machine, study that machine.

Choose a shorter cutoff when stops are rare and each one is worth explaining, such as on an operator-loaded CNC mill. Choose a longer one on a high-speed automatic line, such as a packaging line, where dozens of short jams a shift are normal and the operator has no time to answer for each.

Label short stops or convert them to running time?#

Once you have a cutoff, decide what happens to the stops under it. You can label them as downtime or convert them to running time.

Default to labeling. The stops stay in the record under one reason, so a machine whose short-stop total doubles still stands out on the downtime Pareto.

Convert to running time only when the pause belongs to the cycle and counting it buries the record. A stamping press between strokes is the usual case: the gaps between strokes would otherwise fill a shift with hundreds of one-minute rows. Remember what a converted threshold says: anything under it is not worth reporting, including a jam one minute shorter than the cutoff.

Settings that decide which stops you see#

Four other settings sit near the cutoff and get confused with it. Only two of them change the numbers.

A status color is a display choice. A 4-minute stop is 4 minutes of downtime whether the machine showed green, orange or red.

An alert decides who walks over, not what the report says. Tune each one for its own job, and don’t move the cutoff to make a screen look calmer.

Reduce micro-stops#

Micro-stops respond to the same method as any other loss, measured by count instead of minutes.

• Count stops per hour. The cartoner’s 90 stops in 7.5 planned hours is 12 an hour. Compare machines and weeks on that rate, since a longer shift has more stops.
• Look at when they happen. A cluster after each changeover sends you to the setup. A rise late in the shift sends you to material supply or cleaning.
• Study one machine at a time. Pick the machine with the most stops per hour, watch it for one shift and tally each cause by hand. Chronic causes repeat, so one shift of tallies shows which ones lead.
• Fix one cause, then measure. Compare stops per hour for a week before and after. At 30 seconds each, cutting 12 stops an hour to 6 returns 3 minutes every hour.

Track micro-stops automatically#

A SenseAi on the outside of the machine decides running or stopped every second on the device, with no PLC connection, so a 30-second stop is in the record with its start and end time. Calibration sets how long a reading must stay across a threshold before the state flips, which keeps a 4-second idle between cycles from becoming a stop, as what the sensor decides explains.

The short downtimes rule labels every stop under each machine’s cutoff, 5 minutes by default, or converts it to running time. Continuous processes add a downtime filter for in-cycle pauses.

Status colors change the screen without changing a number. Datwyler’s injection molding plant runs the short-downtime rule beside the shift-start and shift-end rules, and operators and supervisors classify the rest, as its customer story describes.