If you want to perform time synchronous averaging, you typically need one pulse per revolution of the component you want to look at. That can be tricky on a rotating screw compressor because you typically only have access to the coupling. Everything is built into the compressor.
For example, if you want to look at the female rotor on the low-pressure element, how do you access it?
We have something called a pseudo tachometer. So we measure one pulse per revolution, and then we generate an artificial pulse that represents one pulse of the revolution of the next shaft.
Figure 1: Pseudo tachometer
The green pulse strain in Figure 2 is an artificial pulse strain that can be used for time synchronous averaging, monitoring symptoms generated by the shaft.
Figure 2: Artificial one pulse per revolution generated
We usually measure a compressor by placing an optical probe on the coupling. Then we input the number of teeth on the bull gear and on the gear wheel or main rotor, and the system will generate one pulse per revolution of the male rotor.
Figure 3: Compressor with optical probe on the coupling
With this artificial signal, we can perform time synchronous averaging on the male rotor.
For the compressor shown in Figure 4, we input the number of teeth and look at the signals generated by the gear. The spectrum shows 28 orders representing 28 teeth of the gear wheel.
Figure 4: Spectrum showing 28 orders
If you want to perform time synchronous averaging on the female rotor, you also input the gear ratio on the synchronization gears, and the system will generate one pulse per revolution of the female rotor.
Figure 5: Time synchronous averaging of the female rotor
The rotor has six lobes, and the circle plot represents the signal especially well.
