Condition Based Maintenance – Monitoring Tools


I keep getting updates on new products used in the maintenance field through various online subscriptions.

Here is a link that shows the us of Ultrasound devices in the condition based maintenance strategy. I am not trying to sell the product, but am just trying to propagate the techniques involved. Please connect to the link given below and learn more.


Look, Listen and Feel – in Condition Based Maintenance

Hi all,

With due respect to all the gadget geeks and proponents of high-tech equipment to carry out condition based maintenance; the age-old classic forms of observations as indicated below are still valid in the field of condition based maintenance; probably as the first information report function.

Look ………. Listen ………. Feel!

The basics of good maintenance start from the careful, systematic, periodic inspection of equipment and system elements – the first step. Recording of observations is the second step. Analysis of the observations by a maintenance team leader would be the third step.

Essential Safety Precautions for the Look / Listen / Feel Work

Wear all essential personal protection equipment prescribed for each installation. Examples – for high noise areas, ear defenders are a must; eye protection is essential where high dust, fumes, vapours, flying sparks etc conditions exist. Safety shoes are required to be worn in all conditions. Rubber soled shoes with fibre re-inforced toes are to be worn while working on electrical panels and equipment.

Individuals must be deployed for such jobs only after successfully being certified in safety aspects and equipment skills.

Visual inspectionLook

Before starting an equipment or systems: Good maintenance practices exhort users and maintainers to do a full visual inspection of equipment and systems before they are put into use, each time and every time. Such a visual inspection could reveal tell-tale oil or lubricant leaks, discolouration of protective paint due to overheating, corrosion spots, damaged parts, missing elements such as belt / chain guards, dust and debris collection, physical obstruction etc. Clearing all the abnormalities before putting the equipment or systems to use will increase their reliability.

Identifying “Lock Out Tag Out (LOTO)” Conditions: Visual inspection of control (mechanical / electrical) elements will help in identifying the LOTO conditions. In case the equipment is tagged out or locked out; operations are not possible till that condition is cleared by the person who locked it or tagged it.

Running equipment or systems: Periodic visual inspection of equipment or systems while in operation is also essential.

  • This could be done manually by visiting each equipment, looking at the equipment as a whole, checking the relevant critical parameters from their respective meters, checking for abnormal visual vibrations, checking for visible leaks, checking for overheating, checking for spray or flow quality / quantity (example – cooling tower water nozzles),
  • Alternatively, for large installations with high automation and central controls, the visual inspection could be through CCTV cameras, monitoring of parameters through data loggers, online vibration measurement, etc.


This is mostly applicable to equipment with rotating elements (motor driven pumps, fans, compressors etc).

Loose components or sub elements on the equipment may cause audible rattling noise. If left unattended, these could lead to consequential damages.

This technique needs some skill and long involvement of the operator or maintainer with the equipment under his or her charge. The operator / maintainer need to develop a skill on “what to listen to” and on how to identify “wrong noise”. This comes from experience.

On the long run, an operator will be able to make out the change in noise at a motor bearing or a fan air cutting noise due to blade damage. At this point it may be subjective, but a requisition for more precision measurements could be initiated before a major damage occurs.

A long stem screw driver or a simple mechanical stethoscope made out of thin, rigid, long copper tube with a small brass ear cup (a simple washer would do) attached to it could be used as an effective listening aid.

Please be wary that very noisy equipment should not be listened to with unprotected ears and the listening aids mentioned above. Prolonged exposure to loud noise could lead to permanent hearing loss progressively.


The “Feel” factor is an equally important tool in condition monitoring. One needs to be a bit cautious on this aspect since many of the running equipment could have hot surfaces and may not be directly touchable, without causing harm. On the same lines, there could be system elements that run very cold and touching them with unprotected hands could cause cold burns or skin peeling. The Maintenance managers need to decide on what can be touched to feel.

Safety is very important here since the “Feel” actions are generally done on running equipment. Care should be taken to avoid putting the palm very close to moving parts

The “Feel” gives you some idea on the difference in temperature, non-visual vibration level changes, flow quality (turbulent or otherwise), presence or absence of flow, presence or absence of a liquid in a container or pipe, heaviness or lightness of an item, rigidity or flexibility of an item, speed / velocity changes etc. “Feel” is  through the skin and the palm is the best suited body part for the purpose.

Combination of Look, Listen and Feel

Practised together, the above combination provides a very thorough basic condition monitoring technique. experience on the field and safe working habits bring in a slew of benefits in OEE and reliability.

One thing good about this is that it is a value addition to the service rather than eating into a lean and mean budget allocation.

The observations from the above technique could lead to more precise measurements of temperature gradient using a thermal imaging camera, vibration monitoring using hand-held equipment etc.

Visual Factory

Appropriate signage placed at strategic locations could make the Look, Listen and Feel inspection systematic.

Place pictures of eyes where visual inspection needs to be done. Pictures of ears and palm would indicate the listen and feel activities.

Added to these, station markings arrows could be marked on the ground indicating which positions the operator or maintainer should take and direction to face the equipment to make an observation.

Further arrow markings to indicate the direction to be taken while making observations could be done to optimise effort and time taken for observations.

Tail Piece

Smell The human nose can discriminate difference in smells. For example, the smell of overheated or burning oil in a diesel engine has a very recognizable odour.

Heated or burning electric insulation also has a very distinct odour.

The smell of a burning flourescent lamp choke is very discernible.

Smell of a dead rodent in a ventilation duct can be very disturbing.

So, the nose also can be a very reliable sensory organ in equipment / system condition monitoring.

Comments are solicited on my thoughts expressed in this post.


Paralleling of DGs with dissimilar ratings

This is an extract of Web Chat conversations on paralleling of DGs with dissimilar rating – some valuable tips available. Read in sequence fully. The names and organisations have been changed to impersonal tags, but the chat conversations have been edited for better readability alone.

Person A (Org A) 17 Feb 01 22:55

I need to know if it is possible to run a 180KVA DG set in parallel with a 500KVA DG set (Synchronising). If yes, what are the precautions to be taken for safe operations?

Person B (Org B) 18 Feb 01 21:55

If properly engineered and designed, one may run the above DG sets in parallel. They have to be properly:

  1. System grounded (system ungrounded is possible but to be avoided, if possible)
  2. Individually protected
  3. The downstream power distribution must withstand their total short-circuit fault currents and short-circuit MVAs.
  4. Designed for the same frequency
  5. Avoid a short intermittent on-off duty of one of them to keep system stable.
  6. Loaded according to their permissible loading, kVA vs time curves.

Person C (Org B) 19 Feb 01 9:15

In addition to the general factors mentioned by Person B, you need the following specifics:

  1. The governors must be set up for parallel running. This usually means that they must be set for the same percentage droop, so that they can share load in proportion to their ratings. Other control options are available, depending on the type of governor in use.
  2. The voltage regulators must also be set up to share reactive load in proportion to rating. This will usually also mean load droop control, or cross-current compensation between the two AVRs.
  3. Of course, you will need synchronizing instrumentation & controls to parallel the units in the first place. This can be automatic or manual & can be simple or complex depending on your requirements.

Person A (Org A) 19 Feb 01 14:23

Thanks to Person A and Person B for their helpful hints. The system where I am going to implement this is already running 3 sets of 500 KVA in parallel. The neutral (star point) of each alternator is connected to ground through an isolating contactor, only one of which is on at a time (the rest being floating). The latest set of 180 KVA is being added to take care of peak
load requirements.

The paralleling instruments already in place are : Synchroscope (rotating LED type), Check Synchronising Relay (SKE11 Electro-mechanical) and also the dark lamp method!

The other protections are Reverse Power Relay (CCUM21) and Earth Fault Relay (CAG14) for each DG set. Each Alternator is protected by motorised air circuit breakers.

I was wondering if you know any reference book on this subject of synchronising of DG sets.

Person C (Org B) 19 Feb 01 15:10

As far as references are concerned, I suggest that you try the appropriate manufacturer websites. Basler and Woodward governor would be good starting points.

Person B (Org B) 25 Feb 01 16:26


    1. I had to keep my answers in general to avoid any unrelated specifics such as the power management, loading percentages, etc.
    2. The original posting calls for safe operation of the additional 180 KVA DG. The power management strategies are considered on safe side.
    3. More info on DG units and their controls is available over manufacturers such as
  •   Type Governor under Product / Service that will return Governors: Diesel Engines and 2 companies in addition to the mentioned ones in the previous posting.
  •  Type Generator Product / Service that will return Generator Sets: Diesel Electric 181 Companies for good selections on more info

4.   References:

  • Bergen A. R. “Power System Analysis,” Prentice-Hall, Inc., 1986 Page 390 Section 12.5
  • Special Case: Two Generator Units describes in more detail “power control of two generating units,” including frequency droop characteristics

Person A (Org A) 27 Feb 01 10:56

Even as we were corresponding thru Eng-Tips,I was carrying out the installation work (cabling, control wiring etc.)at the site. Yesterday, I commissioned the set (180 KVA, 415V, 3 phase) by synchronizing it with the existing 3 x 500 KVA sets. I am glad to report that the set ran for over 4 hours in a synchronised state without ever tripping. As the load sharing is being done manually, I tried to load the 180 KVA set but could raise it to only to 90 KW. At this loading, it was drawing a current of 200 Amps. This ampere load remained fairly constant even as I decreased the KW load even to 20kW ! I am still scratching my head over that !

I have asked for the governor to be calibrated afresh ( mainly to give me time to think of a viable load sharing scheme ! ) Well, thanks to Person A & Person B for their interest and without whose prompt replies, I would be still groping in the dark.

Person C (Org B) 27 Feb 01 12:35

Glad to hear that you were successful in commissioning the set. A couple of thoughts regarding your results:

– At 90 kW, 200A, 415V you were operating at 144 kVA and a power factor of 0.63; reducing the real power to 20 kW, you kept at 200A with a power factor of 0.14. How is the control mode of AVR set up?
– You may want to try reducing the excitation to increase the power factor up to the rated value (0.80? 0.85?) for this loading. How did the bus voltage respond when the unit came on-line? It should have increased noticeably, so that reducing the unit excitation would bring it back towards nominal.
– Assuming that you are not connected to the grid, you may have to back load off of one of the other running sets to get the 180 kVA unit to pick up more load – it all depends on the droop settings. What control mode is the governor set up for? You may also want to verify that the prime mover isn’t limiting the output due to some mechanical problem.

Person B (Org B) 27 Feb 01 13:31


  1. Power flow simulation by suitable software performing power flow analysis/management could help.
  2. 180 kVA generator is supplying power to the parallel generators. Please, notice that various regulators, controllers, governors, etc. have their boundary conditions and operating regions. If the current setup does not fit the limiting conditions, there may be a need for their customizations.

Person B (Org B) 5 Mar 01 18:42

Suggestion – Visit:


For more info, and help, contact:

Selco USA, Inc. for Load Sharer T4300 for application diagram at 770-455-9110 (Atlanta, GA, USA) or email

That is the end of the extract. Hope that this chat extract was of assistance to you, or at least opened your thought process on the synchronising and paralleling of DG sets.