Quick and flexible mounting of vibration sensors
Magnets are a convenient solution for portable vibration measurements where the sensor needs to be moved quickly between multiple measurement points. However, the choice of magnet and contact surface has a significant impact on frequency response, repeatability and measurement quality.
Magnets for vibration measurement
For handheld vibration measurements, magnets are the most convenient way to mount the vibration sensor. It allows you to move the sensor between different measurement points without drilling, gluing or establishing permanent studs.
This makes magnet mounting particularly suitable for route-based condition monitoring, troubleshooting and periodic control measurements on motors, pumps, gears and fans.
When do magnets make sense?
Magnets are a great solution when:
- you perform vibration measurement with handheld measuring equipment
- The sensor must be moved between many measuring points
- No permanent mounting of sensors on the machine is desired
For permanent installations and for measurements where high-frequency content is important, a fixed stud mount is usually the best solution because it provides the most rigid mechanical coupling and the widest frequency response.
Flat face magnets
Flat face magnets are intended for flat and even surfaces. They provide a quick, semi-Permanent connection between sensor and machine surface and is often the obvious choice for flat bearing housings, motor flanges and machined machine surfaces. Hansford lists this type as suitable for flat surfaces and operating temperatures up to 120°C.
Pole piece magnets
Pole piece magnets are designed for curved or curved surfaces. The special contact shape provides better mechanical contact on e.g. tubular or rounded machine parts, where a standard flat magnet does not have a full contact surface. Hansford describes them as a semi-Permanent solution for curved surfaces, also up to 120°C.
Frequency response - why does the magnet matter?
The mounting method has a direct impact on the measured vibration. When an accelerometer is mounted with a magnet, the connection between sensor and machine becomes differently rigid. This lowers the overall mechanical resonance of the sensor + magnet + surface and thus reduces the usable upper frequency response. As a result, high frequencies are damped earlier and the measurement may be less representative of early bearing damage, gear failure or other high-frequency phenomena.
Hansford writes that stud mounting is the preferred method because it provides the widest frequency response, while magnets provide the lowest frequency response among the common mounting methods.
In practice, this means:
- Stud mounting is best for high-frequency analysis
- Glue/pad typically lies between stud and magnet
- Magnet Good for portable measurements, but more limited at the top end of the frequency range
Several sources also point out that magnet mounting requires particular caution when analysing in the higher frequency range and that data above approx. 1,000 Hz should be considered carefully because the extra mass and less rigid coupling of the magnet can significantly affect the measurement result.
Magnet selection - why we recommend flat magnets
When vibration sensors are mounted with a magnet, the contact surface of the magnet has a major impact on the measurement quality. At TME Solutions, we therefore recommend that you always use flat magnet (flat face magnet) to handheld measuring equipment when possible, or a quick connection point.
A flat magnet gives it Largest contact surface between sensor and machine, which creates a more rigid mechanical connection. The stiffer the coupling between sensor and measuring point, the better the sensor's frequency response, and the more representative the measurement becomes.
In practice, this means:
- Better transfer of vibrations from the machine to the sensor
- Higher usable frequency in the measurement
- More stable and repeatable measurements
- Better ability to identify faults such as bearing damage and gear problems
Therefore, a flat magnet will almost always give Better measurement quality than a pole piece magnet, if the measurement point is flat.
