Computed Order Tracking with Damaged Tacho Pulse
Rotating machinery can be analysed with rotation angle as the reference. This kind of reference is referred to as a tacho or key phasor, reference. A tacho signal can be analog or digital. The end result is usually Single Pulse, a Square Wave or a train of Square Waves. Most signal analysis systems rely on the tacho pulse being in pristine condition. However, the tacho pulse may become damaged when there is sufficient vibration to shake the tacho sensor and/or the rotating system vibration is sufficient for the tacho probe to malfunction. The tacho pulse may then be damaged, and the square...
read moreWaste Incineration and Mechanical Stress Measurement
A dynamic measurement of mechanical stress can be made in numerous ways. One of the worst choices you can make is to measure dynamic stress inside a waster furnace, because: It gets hot – temperatures can get up to 900 C (1650F) inside a waste furnace. Molecule chains are shortened at high temperatures, as a fair portion of them turn into carbides (a.k.a. grinding powder) which fly about inside the furnace. A fair portion of what not is turned into carbide particles becomes highly acid. In some incinerators, explosion is used to remove soot. Particles group into lumps, which can from a great...
read moreSmall Bore – a Low Cost Element that can become very costly
Piping vibration can be troublesome in itself. Small Bore Fittings (a.k.a. Appurtenences) can be worse and usually are the things that first fatigue and break on a piping system and thereby add system risk. There exists vibration fatigue risk criteria for piping vibration failure. These usually are expressed as vibration velocity for the simple reason that it is vibration velocity that is proportional to mechanical stress at resonance, i.e. at the a frequency where we expect vibration/stress to be the highest. Here is a small derivation as to why vibration velocity is proportional to...
read moreWhat is Angle- and Order- Analysis?
When analysing rotating machinery, one may use time or rotation as the reference. A time signal can be resampled from a fixed time resolution, dt, to a fixed angle resolution with the help of the tacho signal. This is what the tacho pulse looks like when resampled from the time domain to a fixed angle resolution (see Figure 1): Figure 1. A tachometer signal resampled from the time domain to the angle domain. One revolution is one square pulse period. The machine is speeding up, as can be seen in the square pulse width being shortened in the time record. (Click figure to enlarge) When...
read moreDIY Encoder for RPM and Torsion Vibration Analysis
Torsion vibration can be difficult to detect in rotating machinery as vibration occurs in a rotating component or drive train. Torsion vibration may result in equipment damage as loads increase and machine internal timing is affected. This post is about optic sensors and the use of a Do It Yourself (DIY) encoder to detect torsion vibration. A tacho signal can consist of one or more pulses per revolution. It can be picked up using e.g. a rotary encoder placed at a free shaft end, magnetic or optic sensors for the purpose of torsion analysis. Torsion analysis can be made using other...
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