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MHC Instrument Standard Mode

Standard Mode signal processing is designed for monitoring rotating machinery operating at speeds down to 35rpm. A key feature of Standard Mode is that there is no need to enter any details relating to the components being monitored such as bearing geometry or shaft speed. Simply mount the sensor on the machine and switch on the instrument; it couldn't be simpler or quicker.

Standard Mode
- typical stages to bearing failure - see also figure below.

Stage 1 - good condition

dB Level ratings at their lowest level for the machine and speed
Distress reading less than 10 (typically less than 5 is very good)

Stage 2 - first signs of a possible problem - a few isolated impacts

dBLevel at their lowest readings for this machine and speed
Distress readings now increased values of 10 and above on some occasions

Stage 3 - an established problem - lots of impacts and roughness

dBLevel still low but increasing
Distress constantly 10 and above

Stage 4 - continuous degradation - increasing frictional activity

dBLevels increase
Distress readings fluctuate

Stage 5 - the approach to final failure

dBLevel increasing at an accelerated rate
Distress mostly 10 and below.

The incoming AE signals are processed in terms of the two parameters Distress® which is a measure of the transient activity on the detected signal (the clicks and crunches) and dB Level is a measure of the overall signal level. Characteristics of these two parameters are as follows:


Distress mode provides an early warning of problems with rotating machinery vibration. It is very sensitive and can even detect poor lubrication at an early stage and acting upon an increased Distress® reading can cure the problem before significant damage has occurred.
  • Most rotating machinery in very good condition has a Distress® reading of 5 or less. If it's more than 10, the machine is usually considered to be Suspect
  • Hence 'Suspect' rotating machines can be identified without previous measurements
  • It is important not to over-react to a high Distress® and prematurely strip down a machine
  • Distress® readings may reduce as final failure approaches and dB Level dramatically increases as illustrated on the figure below

Above: Example of MHC-Memo Pro AE trends on the main bearing of a rock crusher whilst crushing

dB Level 

dB Level is a measure of the mean energy level of the high frequency AE signal. The reading depends on machinery condition as well as machine type, size and speed etc. dB Level readings must therefore be used comparatively - compare with that on other identical machines or with previous readings taken on the same machine (at the same speed - see second graph below)
  • The trend of dB Level with time provides an indication of the rate of deterioration through to final failure
  • In general dB Level is not seen as sensitive to the early stages of a problem as the distress parameter, but dB Level provides a better indication of the approach of final failure

DB level

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