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MHC Acoustic Emission System


MHC (Machine Health Checker) technology has been a valuable tool for Maintenance personnel since it was launched in 1993. The MHC product range from Holroyd includes portable instruments, DIN rail modules and industry-leading smart sensors. The underlying technology is unique in many ways:

  • The AE sensor design uses a novel, very stable and reproducible transducer arrangement. This is the crucial first step in making an effective measurement and a practical monitoring technology - garbage in - garbage out!
  • Signal conditioning circuitry has a wide dynamic range, faithfully processing every signal level. With MHC products there's no need for gain adjustments (either directly or indirectly by entering rotational speed or shaft diameter). This simplifies set-up and eliminates the possibility of erroneous out of range measurements
  • Next the signals are processed in proprietary Standard mode or Super Slo mode to extract pertinent features for early detection of failure. These instantly recognise the existence of problems and directly trends its further deterioration (aircraft engines - remember?). In particular the Distress® parameter in Standard mode and the Extent® parameter in Super Slo mode have a common alert level across a very wide range of machine types and speeds
  • Signal processing is designed to favour the diffuse field rather than the direct arrival signals (i.e. the echo is boosted relative to the initial wave front). As a result, MHC measurements are effectively independent of sensor positioning or orientation. This simplifies sensor mounting onto the machine, whether temporarily or permanently. Easy and simple is a good first step!


It is these unique features, which are incorporated in all MHC products, that gives them their unprecedented capability; simpler, quicker and highly effective. As a result MHC products make an ideal front-line CM tool.

         RP 8           RP 31           RP 14



What does an AE sensor or instrument detect?

When monitoring rotating machinery, AE sensors are able to detect a wide variety of processes of which the most commonly encountered ones are:
  • Friction (e.g. from localised and momentary metal to metal sliding)
  • Impacts (e.g. as rolling elements pass over surface irregularities)
  • Crushing of particulates (e.g. from either dust ingress or wear debris)
The high sensitivity of the AE sensor and the time domain nature of MHC signal processing means that even a single isolated microscopic event can be detected.

The machine faults that give rise to these processes are as follows:
  • Lubrication issues (inadequate viscosity, insufficient volume, presence of particulates)
  • Wear processes (fatigue of surfaces in rolling contact, increased tolerances)
  • Adverse operation (excessive loads, under/over speed & temperature)
  • Poor installation (misaligned/loose/distorted components)
  • Product build-up (out of balance, reduced clearances, increased friction)
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