Working Principle of Keyphasor

Keyphasor is an electric pulse, or trigger, which is derived from a point on a rotating shaft, it serves as a zero phase reference for determining where imbalance is on a rotor.

The most essential factor of any manufacturing plant is the set of machines that help it to conduct operations and processes relevant to its work.

A machine is simply any instrument that receives work as inputs, takes it through a set of processes in order to bring out a set of finish products. The main component of every machine is the fact that it helps work to be done easily and quickly too.

Machines can however breakdown with or without proper maintenance. And the fact is these breakdowns could occur without warning. In an industry, this can prove very expensive as breakdowns can lead to total shutdown of the plant until the defective part is repaired or replaced.

The hope and joy of any mechanical or electrical engineer is to be able to predict potential faults that may be developing in a machine in order to find solutions before these faults lead to larger damage to the machine. Several principles have been developed with the main aim of helping engineers to identify certain key problems that can be linked to more complicated problems in a machine.

One such principle that has been very successful at this task is the Principle of Keyphasor. The principal of keyphasor, like the other principles that have all been put under the process of Condition Monitoring, is used to identify faults in machines.

Condition monitoring basically involves the monitoring of specific parameters or areas in the operation of a machine. By monitoring these parameters, medium to high level changes that take place in these parameters as the machine operates can be identified. These changes can therefore be used as indicators to predict a possible major breakdown.

It is however noted that since principles such as the principles of keyphasor depend on the appearance of a defect within the machine in order to tell whether a major defect is eminent, they do not really predict the defect before it happens. Instead, they rather predict the possibility of a major disaster occurring within the machine.

This does not however take away the fact that they can help the engineer or the machine operator to know when to conduct regular maintenance and which parts of the machine require special attention.

Depending on the type of machine an individual hopes to monitor, the conditions and/or parameters that will be of interest to the individual would vary.

For example; in heat producing machines, valuable insight can be obtained by measuring the temperature within the machine. This is effectively done when reference temperature conditions, with which those from the monitoring can be compared to, are available. In this instance, when the temperature increases drastically above what should be the ideal range, it could signify the development of a problem within the machine. -

On the other hand, the temperature may continue to fall below the reference level; this should provide sufficient grounds for the engineer or the operator to order for inspection and maintenance to be conducted on the machine.

Furthermore, machines that have rotating parts can also be put under condition monitoring in order to prevent serious damage that may require more money to replace parts and cost plants millions of dollars in lost revenue.

For these systems, it is known that the vibrations produced as the parts spin around at hundreds of revolutions per minute can offer valuable means of monitoring them for possible damage. In these systems, the recorded vibrations should be compared to those recorded when the machine was at its best before an accurate prediction can be made on the state of the machine.

Though specialized instruments have been designed to make the process of monitoring the machine for changes in the frequency of rotation, the period of rotation and the harmonics that occur, the data obtained in most cases is quite complex and may take the expert in the area of physics or engineering a bit of time to come out with a logical explanation as to what could be going on inside the machine.

Technological advancement has therefore taken into consideration this difficulty and so brought out systems that monitor and then interpret the information obtained. In such cases, it makes it very easy for the operator to be able to understand the changing trend of the machine’s behavior as these rotating parts wear down with time. The operator of the machine is therefore in a suitable position to inform management of the need to replace worn out parts.

Sometimes, the result obtained from monitoring the machine does not necessarily mean that a part or some parts of the machine are about to break down completely. For this reason, the operator or the one in charge of the machine can employ other effective means of monitoring the progress of the machine.

One additional measure that can be taken involves the use of the principle of keyphasor. A keyphasor is any instrument that relies on the principle of keyphasor for its operation. The keyphasor essentially times the main shaft of the machine; through this, important information about the life of the machine is generated each time the shaft rotates. As a transducer, the keyphaser has the potential to convert one form of energy to the other. This is why under the principle of the keyphasor, the keyphasor is able to take the mechanical energy from the machine shaft and then convert it into a voltage pulse.

The signal from each voltage pulse is used as an important parameter in measuring the overall speed of the shaft. The keyphasor can be put into three categories depending on the way it is used. It could be fixed permanently in a machine in which case it will serve as a proximity transducer. It can also be employed as a magnetic pickup transducer or as the more temporary optical pickup.

In view of the immense advantages of condition monitoring, keyphasors are an integral part of all industries whose machinery relies on rotary motion in order to achieve product conversion. They are also important for monitoring the rotor of ships and boats. By employing keyphasors, a manufacturing company will save hundreds of dollars. The production and use of the keyphasor has brought out a very practical use for the principle of keyphasor.

There are other techniques that are employed in the act of monitoring the operational patterns of machines to try and limit the possibility of a complete breakdown which may prove too expensive for the company involved. It is believed that when these processes are all put together, the lifespan of any machine can be significantly prolonged through the provision of effective and timely maintenance.


A key phasor does not work to remove bow of a shaft. A Keyphasor is simply a eddy current transducer that reads a notch on the shaft in order to give a once per rev voltage pulse.

Used in conjunction with eddy current transducers at the bearings, one can measure the phase angle of the bearing signals relative to the keyphasor. As the shaft makes its closesest approach to the bearing sensors, this part of the shaft corrolates with the direction of the bow in the shaft. This can then be physically marked by the phase angle relative to the keyphasor, since the notch is a known location. This is also how balancing is done.

A keyphasor is not necessary to identify a bowed rotor, but it is helpful in determining the direction of the bow.