Manufacturing & OperationsGlossary

What Is Downtime Tracking?

Also known as: machine downtime tracking, downtime reason codes, stoppage tracking

Definition

Downtime tracking is the systematic recording of when a machine or line stops, for how long and for what reason, so that planned and unplanned stoppages can be measured, categorized and reduced.

Downtime Tracking Explained

A stop is recorded with a start time, end time, machine and a reason code. Machine signals (run, idle, fault) give accurate timestamps. Operators or technicians add the reason, such as no material, changeover, tool break, mechanical failure or waiting on quality. A short, well-designed list of reason codes is critical: dozens of codes produce an unused list, and the code Other becomes the biggest bucket.

Downtime is the availability component of OEE. Analyzing it with a Pareto chart shows the few causes responsible for most lost hours. It also splits planned stops (changeovers, scheduled maintenance, breaks) from unplanned ones, which need different responses: SMED for changeovers, maintenance strategy for breakdowns, material staging for starvation.

ERP-based data collection can capture indirect labor or machine down transactions, but dense machine data usually comes from an MES, a machine monitoring system using MTConnect or OPC UA, or PLC counters. The data is also used by maintenance modules to compute MTBF and MTTR and trigger work orders.

Why It Matters

You cannot reduce losses you do not measure, and manual estimates usually understate them.
Reason-coded stops direct improvement effort to the biggest cause rather than the loudest complaint.
It supplies the availability figure for OEE and the failure data for MTBF and MTTR.
It supports capacity decisions: spare hours may be hiding in downtime, avoiding premature machine purchases.

In Practice

A machining cell reports 62 percent availability. Reason-coded data over four weeks shows 35 percent of lost time is waiting for material, 30 percent is changeover, 20 percent is tool breakage and the rest is a mix. The team stages material at the cell and standardizes tool presets, raising availability toward the high 70s without any new equipment purchase.

Frequently Asked Questions

What are common downtime reason codes?

Changeover, no material, no operator, tooling, mechanical or electrical breakdown, waiting for quality, planned maintenance and break. Keep the list short and review it regularly.

Can downtime be tracked without sensors?

Yes, with operator entries on a terminal, but accuracy depends on discipline. Machine signals give precise timing; operators add the reason.

How does it relate to OEE?

Downtime determines availability, one of the three OEE factors alongside performance and quality.

Related Terms

OEE (Overall Equipment Effectiveness)

OEE (Overall Equipment Effectiveness) is a manufacturing metric that multiplies Availability, Performance, and Quality into a single percentage showing how much of scheduled production time an asset spends making good parts at its rated speed.

MTBF (Mean Time Between Failures)

MTBF (Mean Time Between Failures) is the average operating time a repairable asset runs between consecutive failures, calculated as total operating time divided by the number of failures in that period. It measures reliability, not expected lifetime.

MTTR (Mean Time To Repair)

MTTR (Mean Time To Repair) is the average time required to restore a failed asset to full operating condition, calculated as total repair time divided by the number of repairs. It measures maintainability rather than reliability.

SMED (Single-Minute Exchange of Die)

SMED (Single-Minute Exchange of Die) is a structured method developed by Shigeo Shingo for reducing equipment changeover time to under ten minutes, primarily by converting setup steps that require the machine stopped into steps performed while it still runs.

TPM (Total Productive Maintenance)

TPM (Total Productive Maintenance) is a company-wide approach to equipment reliability that shifts routine care to operators, builds structured planned maintenance, and targets the elimination of breakdowns, speed loss, and defects caused by equipment condition.

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Downtime Reason Code Hierarchy Reference

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A starter list of downtime reason codes arranged in a hierarchy, mapped to the six big losses and to planned or unplanned status.

Download:

Level 1 group	Level 2 reason	Big loss	Planned or unplanned	Example
Equipment failure	Mechanical breakdown	Breakdowns	Unplanned	Broken drive belt on conveyor
Equipment failure	Electrical fault	Breakdowns	Unplanned	Contactor failure on a spindle motor
Equipment failure	Controls or software fault	Breakdowns	Unplanned	PLC fault that needs reset and restart
Equipment failure	Tool breakage	Breakdowns	Unplanned	Broken end mill mid cycle
Setup and changeover	Product changeover	Setup and adjustments	Planned	Switch from part A to part B
Setup and changeover	Tooling change	Setup and adjustments	Planned	Fixture swap
Setup and changeover	First off approval wait	Setup and adjustments	Unplanned	Waiting for quality to approve the first piece
Setup and changeover	Adjustment after setup	Setup and adjustments	Unplanned	Re-zeroing offsets after a trial part
Material	Material shortage	Breakdowns	Unplanned	Bar stock not delivered to the cell
Material	Wrong or incorrect material	Breakdowns	Unplanned	Wrong lot staged
Material	Material jam or feed fault	Small stops	Unplanned	Part jam at the feeder
Minor stoppage	Sensor blocked or misread	Small stops	Unplanned	Dust on a photo eye
Minor stoppage	Cleaning during run	Small stops	Unplanned	Chip clearing
Minor stoppage	Operator intervention	Small stops	Unplanned	Manual reset of an alarm
Speed	Running below rated speed	Reduced speed	Unplanned	Feed rate reduced to avoid chatter
Speed	Worn equipment	Reduced speed	Unplanned	Machine run slower to hold tolerance
Quality	Startup rejects	Startup rejects	Unplanned	Scrap until the process warms up
Quality	Production rejects	Production rejects	Unplanned	Out of tolerance part found at inspection
Quality	Rework	Production rejects	Unplanned	Part sent for secondary operation
People	No operator available	Breakdowns	Unplanned	Operator pulled to another line
People	Shift change handover	Setup and adjustments	Planned	Scheduled handover time
Planned stop	Scheduled maintenance	Not a loss in OEE	Planned	Preventive maintenance slot
Planned stop	Break or meal	Not a loss in OEE	Planned	Scheduled break
Planned stop	No demand or no order	Not a loss in OEE	Planned	Nothing scheduled
Utilities	Power or air supply loss	Breakdowns	Unplanned	Compressed air pressure drop

Keep the list short enough that operators can pick a reason in a few seconds. Whether a reason counts against OEE depends on your planned time rules, so confirm before you load the codes into a system.

Review your downtime code set

Optional review of your reason code list and how stops flow into reports.

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