Video and Audio clips
  • Quickly identify and isolate expensive gas leaks
  • How to attach MHC sensors
  • The effect of adequate lubrication
 
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Video and Audio Clips

Seven examples are given below covering video and audio clips. The first four cover video clips for the application of MHC Technology and the final three are audio clips illustrating the signal from a good, damaged and poorly lubricated bearing. 




Quickly identify and isolate expensive gas leaks.
 

MHC instruments can be fitted with a special microphonic sensor specifically adapted to detect ultrasonic noise generated by gas leaks.  

That is not just compressed air but any industrial gas including steam and refrigerant.  The leak does not have to be large or even vented directly to atmosphere.  We can detect it allowing maintenance to be planned and professionally executed. 

 
How to attach MHC sensors.

In this example, a portable sensor is used along with coated steel mounting pad permanently fixed to the machine. The sensor has a magnetic head to ensure a firm attachment to the pad.  Grease is used for a good acoustic coupling between the pad and sensor.  Various designs are available for unusually wet, humid or hot applications.

Sensors can be also fixed permanently for monitoring critical applications or where failure mode can be rapid. 

 
The effect of adequate lubrication.  

Have a look at this clip but also a similar Audio clip in the column below.  Both illustrate how the AE signal changes with adequate lubrication.  

The bearing starts dry, no oil film and lots of small impacts. Both Distress® and dB Level indicate something is wrong. When oil is added the readings settle but only after the oil film has become stable. Distress® eventually indicated that no long term damage has occurred and adequate lubrication has fixed the problem. 

 

How to take measurements

MHC Technology is easy to apply and provides useful data from day 1. This example was taken at a water works.  A maintenance engineer has approached a pump unit and wished to examine the motor and aerator bearings. A full set of readings was available within 1-2 minutes of first arriving at the site.

In this instance Distress® levels were all below the warning level of 10 (actually below 5 on this unit) and no further action was necessary.  The unit continued to run trouble free until the next scheduled maintenance period.


A reason for the solid success of the MHC range is the clarity of the detected signals (a direct consequence of the unique sensor design and signal processing). MHC products exclusively detect activity in the vicinity of 100kHz and dramatically filter out background noise and vibrations. The trick is then to very rapidly demodulate the amplified sensor signals. The carrier signal is stripped away from it's amplitude modulations which occur at audio frequencies. The effect is to produce an audio signal which is very sensitive to fault signals (such as impacts and friction), yet insensitive to everyday noises and vibrations. 
 
This method gives a much clearer sound than listening directly at audio frequencies. It also has the added benefit of sounding 'right' (i.e. not like electronically generated pings). Engineers tell us that they can intuitively tell what's happening from the headphones signal. Of course there is a tendency for different people to interpret the same sounds differently. This is where the advanced signal processing of Distress® and dB Level values comes into its own.


This is how the AE signal changes when a dry bearing is properly lubricated.

Dry bearings have little or no oil film. Hydrodynamic lubrication or an oil wedge cannot form and there is frequent metal/metal contact both with the races and the cage.

Once sufficient oil is applied (half way through the track) , an oil film rapidly  forms with a vast improvement in expected bearing life. 
The sound of a damaged bearing.  

For whatever reason bearing damage has occurred. Common reasons are fatigue, poor lubrication, overheating or overload.

Both rollers and the race (especially the inner race) have been damaged as can be seen in the photograph. 
The sound of a good bearing. 

This is the sound that is most commonly heard, the quiet swish of a well lubricated bearing performing to design.  Most bearings are like this.

MHC technology lets you rapidly identify those that are not so that action can be planned and taken to fix or replace. 
   

 
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