Machine Health Monitoring provides efficient methods by reducing downtime and preserving assets. Vibration monitoring will enable preventive maintenance on almost any type of machine. It could be done by recurrent control or real time analysis. Condition monitoring involves fixing sensors to mechanical parts of the machines in order to track failures and malfunctions.
|Components Monitored||Possible Faults||Frequency Range|
|Support structure||Imbalance, external vibrations, oil-whirl||DC 0 Hz – 100 Hz|
|Shaft, gear, slide-bearing||Imbalance, hunting mesh, misalignment, looseness||DC 0 Hz – 1’000 Hz|
|Gear, bearing||Mesh faults, gear pitting, shocks||100 – 10’000 Hz|
|Bearing, motor||Acoustic vibrations||10’000 – 100’000 Hz|
Low frequency monitoring (from DC 0 Hz to 1000 Hz) includes:
• Hunting tooth detection
• Low speed fan monitoring in cooling towers
• Low speed agitators in industries
• Geophysical measurement equipment
Explanation of the System
MHM will be set up according to the type of faults to analyze, by measuring frequency ranges. In general, spectrum analysis is used to identify the different vibration frequencies.
MHM requires reliable sensors, resistant to possibly high temperature and repetitive shocks. The system must be able to operate in wet and corrosive environments (e.g. in a cooling tower). Furthermore, the sensors must last as long as the component analyzed.
Monitoring at low frequencies implies two major requirements. First of all, the noise produced by the sensor must be as low as possible: the least amount of electronic noise generated, the quicker a fault is detected. As an example, specific CNC machines require sensors with a noise level between 75 and 90 dB, operating at a low frequency (DC 0 Hz – 1’000 Hz). Secondly, a high voltage output is key to set a sufficient threshold.
The vibration sensors are accommodated for this application, particularly the VS1000 series. The good ranges of measurement would be ±2g, ±5g and ±10g. The VS1002 sensor’s property is its very low noise level of 7 µg/√Hz – equivalent to class C at 90 dB. The VS1000 sensors have a non-linearity of 0.1% (typ. full scale), a linear frequency response from DC 0 Hz to 2500 Hz at ±5% FS, up to 7000 Hz at -3 dB. A maximum shock resistance of 6000g ensure a strong survivability of the sensors.