The desired length of uninterrupted measurement is the first criterion that should be considered when selecting a torque measurement system. Significant costs can be avoided through the selection of a simple system. Often, torque measurements are only required temporarily for validation of theoretical models, commissioning, or diagnostic purposes. In these cases, strain gage systems are commonly used. An example of a temporary installation of a strain gage system is shown in Photograph 6a. The gage and RF transmitter are attached to the rotating shaft, in this case a shear spacer. A brass hoop antenna is installed around the circumference of the shaft and receives the RF signal from the transmitter. In certain designs, this type of setup can also serve to provide inductive power to the transmitter, eliminating the need for batteries. Photograph 6b shows a permanent installation using
a similar strain gage telemetry system. The electronic components on the rotating shaft are protected by the rubber and metallic enclosures mounted to the shafts. An alternate enclosure used to protect the gages and transmitter is shown in Figure 7a. This particular system does not require a hoop antenna and transmits the signal wirelessly to a receiver and processing module. In higher-speed applications, the mounting of electronics on a rotating shaft can introduce imbalance, creating other problems. In these cases, the transmitter assembly mounted to the shaft should be counter-balanced with a weight installed at 180 degrees. In balance-sensitive applications, the components should be dynamically balanced once the telemetry system is installed. Tubular shafts provide an option for the gages and wiring to be installed on the inner diameter which provides additional protection and secures the wiring (Figure 7b).
Photographs 6a and b- Strain Gage Telemetry System Installation on shear spacer (left) and permanent installation on counter-rotating shafts (right).
Figures 7a and b: Enclosure and mounting options for an externally shaft mounted transmitter (left) or gages and wiring installed on the inner diameter of a tubular shaft/spacer section (right).
As with linear vibration, the time-waveform and FFT spectrum of the torque data provide the analyst with information needed to identify the torsional vibration severity and source, respectively. Values from the time-waveform can be directly related to stress, which allows for evaluation of the drivetrain reliability in terms of fatigue and yield safety factors.
72 | ISSUE 109 | SEP 2024 | THE REPORT
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