Equipment Health Index: Definition

What Is an Equipment Health Index?

An equipment health index (EHI) is a calculated score that reflects the current physical condition of a machine. Rather than requiring a technician to interpret multiple separate readings, an EHI collapses vibration data, temperature trends, lubrication analysis, and other diagnostic inputs into a single number.

Most EHI scales run from 0 to 100, where 100 represents an asset in perfect condition and lower scores indicate increasing levels of degradation or fault risk. Some systems use color-coded thresholds: green for healthy, yellow for watch, and red for critical.

The value of an EHI is that it gives a maintenance manager or reliability engineer an immediate read on asset condition without needing to review individual sensor graphs. When the score drops, it is a signal to investigate and act.

How Is an Equipment Health Index Calculated?

Calculating an EHI involves three steps: data collection, scoring, and aggregation.

Step 1: Data Collection

Sensors collect real-time readings from the asset. Depending on the machine type, this includes vibration amplitude, bearing temperature, motor current, lubrication particle count, shaft alignment, or acoustic emission levels.

Step 2: Parameter Scoring

Each parameter is compared to its normal operating range or baseline. A reading within the normal range scores well. A reading approaching or exceeding the alarm limit scores poorly. The scoring function is typically non-linear: small deviations matter less than readings near the failure threshold.

Step 3: Weighted Aggregation

The individual parameter scores are combined using weights that reflect each parameter's contribution to failure risk for that asset type. For a centrifugal pump, vibration and bearing temperature might carry the highest weights. For a gearbox, lubrication condition might be weighted more heavily. The result is the equipment health index.

Key Parameters Used in an Equipment Health Index

The parameters that feed an EHI depend on the asset class. These are the most commonly used inputs across industrial rotating equipment:

Equipment Health Index vs OEE: Key Differences

The equipment health index and overall equipment effectiveness (OEE) are both essential metrics, but they measure different things and serve different purposes.

A machine can have a declining EHI while still showing acceptable OEE scores. That is exactly the scenario where the EHI provides value: it warns you before the failure that will eventually drive OEE down.

How to Use Equipment Health Index in a Maintenance Strategy

The EHI is most useful when it drives specific actions, not just awareness. Here is how maintenance teams use it in practice:

Set Thresholds and Alerts

Define action thresholds for each asset or asset class. A common approach uses three bands: healthy (70 to 100), watch (40 to 69), and critical (below 40). When the EHI crosses into the watch band, the system generates a notification. When it enters critical, it triggers a high-priority work order.

Prioritize Work Orders by EHI

When multiple assets need attention, maintenance planners can rank work orders by EHI score rather than by failure date alone. Assets with the lowest EHI and the highest criticality ranking get scheduled first.

Track EHI Trends Over Time

A single EHI reading shows current condition. A trend over weeks or months shows the rate of degradation. A fast-declining EHI on a critical asset is a more urgent signal than a slow decline on a non-critical one.

Connect EHI to Predictive Maintenance Interventions

EHI integrates directly with predictive maintenance programs. The index gives the maintenance team a clear, defensible trigger for scheduling proactive repairs rather than waiting for a fixed calendar date or an actual failure.

Benefits of Tracking Equipment Health Index

• Earlier fault detection: Declining EHI scores surface developing problems before symptoms become visible.
• Reduced unplanned downtime: Proactive interventions triggered by EHI thresholds prevent the sudden failures that cause production stoppages.
• Smarter maintenance scheduling: Teams schedule repairs based on actual condition, not arbitrary time intervals.
• Better resource allocation: Focus technician time on assets that actually need attention.
• Audit trail for asset decisions: EHI history provides documented evidence to support replace-or-repair decisions.

Equipment Health Index in Condition Monitoring Platforms

Modern condition monitoring platforms calculate EHI automatically from connected sensors, updating the score in real time as new readings come in. The score is typically displayed on an asset condition management dashboard alongside trending charts, alarm history, and open work orders.

Asset performance management (APM) systems go a step further, using EHI scores as inputs to reliability models that estimate remaining useful life and forecast failure probability across an entire asset fleet.

For teams that monitor equipment monitoring data across multiple sites, EHI makes it practical to manage hundreds of assets by exception: only investigate those with falling scores.

Frequently Asked Questions

The Bottom Line

An equipment health index turns complex, multi-parameter sensor data into one clear signal: is this machine healthy or not? For maintenance teams managing large fleets of rotating equipment, that simplicity is operationally powerful. A falling EHI score tells you which asset to prioritize, how urgently to act, and whether the trend is worsening. Combined with a condition monitoring platform that calculates and tracks EHI automatically, it gives maintenance and reliability engineers the early warning system they need to prevent failures before they happen.