This article is for plant managers, production managers, continuous improvement leads and maintenance managers whose machines run, do not stop, and still produce less than planned. It covers the least visible OEE loss: speed loss, when a machine runs below its reference rate.
- A running machine can produce well below its reference rate.
- This speed loss appears in no downtime log.
- Slow running and micro-stops have different causes and actions.
- Only part-by-part measurement makes the speed gap visible.
A running machine is not necessarily a machine running at rate
On the shop floor, a running machine is seen as a healthy machine. No warning light, no alarm, no intervention. Yet if it produces 80 parts where it should produce 100 in the same time (fictitious example), it loses the equivalent of one fifth of its run time. This loss shows up in no downtime log, because there was no stop.
In the OEE calculation, it lands in the performance rate: the ratio between what was produced during run time and what could have been produced at the reference rate. That reference rate still has to be right. If it has been lowered over the years to match reality, speed loss disappears from the calculation without disappearing from the shop floor.
Deliberate or suffered reduced speed
Not all speed reductions are equal. Two situations must be distinguished.
- Deliberate reduced speed. A setting for a difficult product, a sensitive raw material, a quality instruction, a setter who slows down after a series of incidents. The decision may be legitimate, but it must be recorded, with its reason and planned duration. Otherwise the temporary slowdown becomes the norm.
- Suffered reduced speed. Component wear, fouling, irregular upstream supply, downstream saturation, one operator covering two stations. The machine cannot do better, and nobody decided it.
In both cases the rule is the same: the reference rate remains the machine’s nominal rate for the product concerned, and the gap is measured. A deliberately reduced rate is justified by a reason; it is not hidden in the standard.
Slow running and micro-stops: two different losses
Both losses weigh on the performance rate and are often confused. Yet they are neither detected nor treated the same way.
| Criterion | Micro-stops | Slow running |
|---|---|---|
| What happens | The machine stops for a few seconds or minutes, then restarts | The machine does not stop, but its cycle gets longer |
| Signal to watch | No output over a short period | Time between two parts above the reference cycle time |
| Shop floor visibility | Low: too short to be noted | Very low: nothing can be seen |
| Typical causes | Jams, poorly set sensors, occasional feed faults | Wear, cautious settings, upstream or downstream constraints, settings never reviewed |
| Typical actions | Cause Pareto, adjustments, reliability work | Settings review, maintenance, line balancing |
A line can have few micro-stops and a lot of speed loss, or the reverse. Lumping them into one category leads to poorly targeted action plans.
How to detect speed loss
- Set the reference rate per product, from the manufacturer’s data or the best sustained rate observed, and document it.
- Measure every cycle or every part automatically, to compare actual time with reference time continuously, not only at the end of the shift.
- Separate stops, including short ones, from run time, to isolate the speed gap while the machine is running.
- Compare by product, by shift and by period: a slowdown that appears only on one shift or one product immediately points the analysis.
- Track the trend: a slow drift in rate over several weeks often signals wear or fouling.
For example (fictitious figures, for illustration only), a press with a 20-second reference cycle runs at 23 seconds on the night shift, since a setting change that was never reversed. No stop is recorded, but that shift loses about 13% of its possible output during run time. Once the gap is visible, the fix takes a few minutes.
Common causes and actions
- Settings never reviewed. Speeds lowered during an incident and never raised again. Action: periodic review of settings against the reference rate, with a written reason for every gap that is kept.
- Wear and fouling. Belts, tools, guides, nozzles. Action: compare rate drift with maintenance interventions and adjust preventive frequency.
- Upstream or downstream constraints. Irregular supply, saturated conveyor, slower downstream machine. Action: look at the whole line, not the isolated machine, and address the real constraint.
- Material and product. Difficult batches, new part numbers. Action: one reference rate per product and gap tracking per batch.
- Organisation. Operator shared between several machines, waiting for inspection. Action: compare gaps by shift and review staffing.
Measure so the loss stops being invisible
Speed loss only becomes visible with continuous, part-by-part measurement. TEEPTRAK provides it with a module wired into the electrical cabinet and a sensor at the line, about one hour of installation per machine, with no connection to the PLC. OEE is available within 48 hours, separating stops, micro-stops and speed gap. Teams see when a machine runs below its reference rate and can link the gap to a product, a shift or an intervention. TEEPTRAK is deployed in more than 700 plants in over 30 countries.
Further reading
- The 6 big losses: what your manual log doesn’t see
- Eliminating Micro-Stops: Pareto, Top 3 Root Causes, and Targeted SMED Project
- Injection molding presses: tracking downtime and cycle time drift in real time
FAQ
Can the reference rate be lowered to match reality? Not without a documented technical reason. The reference rate must reflect what the machine can do on that product. Lowering it removes the loss from the calculation, not from the shop floor.
Is a deliberate slowdown a loss? Yes in OEE terms, because the machine produces below its reference rate. It may be justified, but it must be recorded with its reason, so it can be reviewed and lifted as soon as possible.
What is the difference between slow running and a micro-stop? A micro-stop is a short interruption: the machine produces nothing for a few seconds or minutes. Slow running is a longer cycle without interruption. Both weigh on the performance rate, but their causes and actions differ.
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