A vibration sensor bolted to the wrong spot can look perfectly healthy while a bearing is failing, or alarm all day because it sits on a flexing cover. Placement decides how much of a fault signal ever reaches the sensor, and no analytics layer can recover a signal that was never captured. This guide shows where to put each sensor type on motors, pumps, gearboxes, air handlers, and chillers in commercial buildings, and how Oxmaint maintenance software records every mount point so readings stay comparable year after year.
PdM Sensor Placement Guide: Where to Put Every Sensor Type
Predictive maintenance only works when the sensor sees the fault. Mount close to the bearing, on solid metal, in a repeatable position, and document it so the next technician puts the next sensor in the same place.
Why placement matters more than sensor brand
Vibration energy weakens and changes character each time it crosses a joint, gasket, or thin panel. The shorter and stiffer the path from the defect to the sensor, the more of the original signal you keep.
Six placement rules that apply to every asset
Manufacturer guides and standards such as ISO 20816, the successor to the ISO 10816 series, agree on the same basics: measure on bearing supports or structural parts that respond to the machine's forces.
- Mount on the bearing housingBearings are where most rotating faults start. Put the sensor as close to the bearing centerline or load zone as the guarding allows.
- Keep the path short and solidFewer joints between the defect and the sensor means less signal loss and fewer reflections.
- Avoid thin or flexible surfacesSheet metal covers, fan shrouds, and guards ring at their own frequencies and corrupt the reading.
- Use clean, flat bare metalPaint, rust, grease, and curved surfaces weaken contact. Prepare the surface before every mount.
- Pick one orientation and keep itConsistent axes across similar assets make fleet comparison possible and trends trustworthy.
- Document the exact spotA photo, a position label, and the mount type stored on the asset record let anyone repeat the install.
Mount point map by asset type
Use this as a starting map for common commercial building equipment. Confirm details against the manufacturer's drawings, and never drill or modify pressure-retaining parts without OEM approval.
| Asset | Primary mount points | Sensor types | Placement notes |
|---|---|---|---|
| Electric motor | Drive end and non-drive end bearing housings | Vibration, temperature | Smaller motors may need only the drive end. Avoid the cooling fan shroud. |
| End-suction or inline pump | Motor bearings, pump inboard and outboard bearing housings | Vibration, temperature, pressure | Add an axial position at the thrust bearing when thrust load or misalignment is a concern. |
| Vertical pump | Upper and lower motor bearings, pump bearing area, column or casing | Vibration, temperature | Casing and base readings help catch looseness and resonance in the support structure. |
| Belt-driven fan or AHU | Both fan shaft pillow block bearings, motor bearings | Vibration, temperature, current | Place on the bearing housing, not the fan casing. Belt wear shows up as a change in running speed signature. |
| Direct-drive fan or FCU motor | Motor drive end, fan side bearing | Vibration, current | Low-cost units often justify a single sensor at the most accessible bearing. |
| Gearbox | Input shaft bearing, output shaft bearing, housing near the gear mesh | Vibration, temperature, oil condition | Position the sensor to shorten the path from the gear mesh and bearings. Multi-stage boxes need more than one point. |
| Cooling tower fan drive | Motor bearings, gearbox housing, fan shaft support | Vibration, temperature | Wet, corrosive conditions call for sealed sensors and corrosion-resistant mounting hardware. |
| Chiller compressor and motor | Compressor bearing housings, motor bearings, gear housing where fitted | Vibration, temperature, current, pressure | Agree mount points with the chiller OEM. Pair vibration with process data for a fuller picture. |
Where each sensor type belongs
Each sensor answers a different question. Place it where that question is best answered, rather than putting every sensor in the same location.
Choosing the mounting method
The mount is part of the measurement. A loose or compliant mount filters out the higher frequencies where early bearing faults appear.
| Method | Strength | Limit | Best used for |
|---|---|---|---|
| Threaded stud | Best contact and frequency response | Needs a drilled and tapped hole | Permanent installs on critical assets |
| Epoxy-bonded stud pad | Strong contact without drilling | Needs cure time and a prepared surface | Most wireless sensor deployments |
| Adhesive on the sensor base | Fast and low cost | Surface must be flat and smooth | Standard motors and housings |
| Magnet | Quick to move and test | Reduced high-frequency response, can shift over time | Route-based checks and trials |
| Fin clamp | Reaches the motor case between cooling fins | Must make direct contact with the case | Finned motors with guarded bearings |
Good placement versus common shortcuts
Shortcuts that waste sensors
- Mounting on the fan shroud because it is easy to reach
- Placing the sensor on a painted or rusty surface
- Using a different spot on each identical pump
- Putting one sensor on the baseplate and expecting bearing alerts
- Moving sensors during repairs without recording the change
- Skipping the axial position on thrust-loaded pumps
Practices that protect the signal
- Opening a guard or adding a mounting pad to reach the bearing
- Grinding to bare, flat metal and cleaning before bonding
- Using one standard layout for each asset class
- Pairing a structure reading with each bearing reading
- Updating the asset record whenever a sensor is moved
- Adding the axial point where thrust or misalignment matters
Orientation: radial, vertical, and axial positions
Three-axis sensors reduce the need to align a particular axis with the machine's motion, but a consistent position still matters for comparison.
Radial horizontal
The workhorse position for most bearings. It shows imbalance, looseness, and many bearing defects, and it is the usual choice when only one position is possible.Radial vertical
Useful on foot-mounted machines where stiffness differs by direction, and for catching soft foot and base issues.Axial
Highlights misalignment and thrust bearing wear. Place it at the bearing that carries thrust, such as the pump inboard bearing.Commissioning timeline for each sensor
A disciplined install takes minutes more than a rushed one and saves months of confusing data.
- Survey the assetLocate bearings, guards, access limits, and heat or moisture exposure.
- Pick and label the pointChoose the mount position and give it a standard name such as pump inboard.
- Prepare the surfaceRemove paint and rust, flatten, degrease, and let solvents dry.
- Mount and secureBond or fasten per the sensor maker, route cables clear of hot and moving parts.
- Capture a baselineRecord readings at normal load right after install, ideally on a known healthy machine.
- Record in the asset fileStore the photo, point name, mount type, and baseline against the asset.
Give every sensor point a record
Store mount locations, photos, baselines, and inspection history against each asset so a sensor swap never breaks your trend.
Setting baselines and alarm limits after placement
Raw numbers only become decisions when compared with something. Your own history on a correctly placed sensor is the most reliable reference.
Start with the standard
ISO 20816 gives severity guidance by machine class and support type, which is a sensible first alarm reference before you have history.Move to your own trend
After several weeks at normal load, set warning and alarm levels relative to each machine's baseline rather than a generic number.Compare identical assets
Consistent placement lets you compare pump A with pump B. A machine that drifts from its twin deserves a look.Tie alerts to action
Each alarm level should map to a defined response, such as inspect, retest, or raise a corrective work order.Placement mistakes and the symptoms they cause
| Mistake | Symptom in the data | Fix |
|---|---|---|
| Sensor on a cover or shroud | Noisy readings, false alarms, unexplained peaks | Relocate to the bearing housing or a rigid pad |
| Loose or aged adhesive | Readings slowly fall with no change in condition | Re-bond and re-baseline, add a mount check to routes |
| Different positions on identical assets | Fleet comparison shows odd outliers | Adopt a standard layout per asset class |
| Too far from the bearing | Early faults appear late or not at all | Move closer, add a mounting block if needed |
| Cable strain or heat exposure | Dropouts and intermittent data | Reroute cables and secure with clamps |
| Sensor moved without notice | Step change in trend after maintenance | Log every move and reset the baseline |
KPIs that show whether placement is working
How Oxmaint supports a sensor-based maintenance program
Oxmaint is maintenance management software. It does not replace your sensor hardware or analytics, but it keeps the assets, inspections, and follow-up work organized around them.
Asset hierarchy
Keep motors, pumps, fans, and chillers in one structure so every sensor point sits under the right parent asset.Inspection checklists
Add mount checks, cable checks, and visual surface checks to routine rounds on mobile.Corrective work orders
Turn a confirmed condition alert into a tracked work order with an assigned technician and due date.Preventive maintenance scheduling
Schedule lubrication, alignment, and sensor verification on fixed intervals alongside condition-based triggers.Equipment history
Link repairs and part changes to each asset so a trend shift can be explained by a recorded event.Reporting
Review alert response, backlog, and recurring failures by asset class and building.Site conditions that change the mount plan
The right spot on a drawing is not always the right spot on a rooftop in July or in a damp plant room. Check the environment before you commit to a position.
Heat and hot surfaces
Check the sensor's temperature rating against compressor housings, steam-heated equipment, and sun-baked rooftop units. Adhesives soften when they run hot, so confirm the bond rating too.Moisture and corrosion
Cooling towers, pump rooms, and exposed rooftop equipment need sealed sensors, protected cable entries, and stainless or coated hardware to avoid slow failures.Guards and access
If a guard blocks the bearing, modify it properly or add a mounting pad outside it. A poor spot chosen only for convenience produces weak data for years.Wireless signal and enclosures
Metal enclosures and dense plant rooms can weaken radio links. Test the signal at the chosen point before bonding the sensor, and note any gateway location on the asset record.Which assets deserve sensors first
A sensor on every motor is rarely justified. Rank assets by consequence of failure, then spend your placement effort where an early warning changes the outcome.
Critical and shared
Chillers, main chilled and heating water pumps, large air handlers, and fans that serve many occupants. Use the full mount layout and capture baselines carefully.Important with a backup
Duty and standby pump pairs and redundant fans. One or two positions per machine are often enough, and comparing the pair adds value.Low consequence
Small fan coil units and minor exhaust fans can stay on routine inspections and preventive tasks rather than permanent sensors.Sensor placement FAQs
How many vibration sensors does a pump and motor need?
Four radial positions, one at each bearing, is a common full layout, with an axial point at the thrust bearing when needed. Critical assets justify all points, while minor ones may use one or two.
Can I mount a sensor on the motor fan cover?
Avoid it. Covers and shrouds flex and resonate, which distorts the signal. Use the bearing housing or the motor case near the bearing instead.
Does it matter which axis the sensor faces?
Three-axis sensors do not need a particular axis aligned, but consistent placement across similar assets still matters for trending and comparison.
How do I keep placement consistent across technicians?
Store a photo and position label on each asset record. Oxmaint asset records give every installer the same reference.
Where should a building start with condition monitoring?
Start with critical pumps, large fans, and chillers where failure disrupts occupants. Book a demo to plan the asset structure.
Make every sensor reading trustworthy
Connect sensor points, inspections, and corrective work in one maintenance system built around your assets.
