Telemetry system mining automation determines vibration behavior of large fans

In the Russian mine
Telemetry system determines vibration behavior of large fans

Two large fans from Germany ensure ventilation of the Russian nickel and copper ore Severny Gluboky. To optimize the speed control of fans traveled the engineers for commissioning in the remote region of Murmansk, north of the Arctic Circle. With the help of a new radio-telemetry system they were able to determine the natural vibration behavior of the motor shaft in a short time.

The company projected Howden fans and developed large fans for mines, tunnel, wind tunnels, and power plants. The products range from simple fixed pitch axial fans to sophisticated Axial fans with adjustable blade angle. Since the 50s, the Swabian company also deals with ventilation systems in mines. The global orientation makes this service calls for commissioning and maintenance of the enormous facilities around the globe required.

Verification of the self-oscillating behavior



It verschlägt the engineers sometimes in remote areas, such as in the Murmansk region on the Russian Kola Peninsula north of the Arctic Circle. There are two large fans from Heidenheim in the pit ventilation in the nickel and copper ore Severny Gluboky under arctic conditions are in use.
    A typical measurement task in such an operation is to determine the natural vibration behavior of the motor shaft of the fan. During the design and construction of the plant by the plant operator receives information about shafting calculating critical frequencies or speeds that can reach the fan during operation. Operating conditions are possible in which the speed of the fan goes through this natural frequencies, appropriate countermeasures to prevent undesirable resonance effects must be taken. The project in Severny Gluboky the computational modal analysis yielded a first natural frequency of the torsional vibration in the region below the rated speed of 750 rpm (equivalent to 12.5 Hz). This frequency must therefore go through the process start and stop the system.

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However, can the acceleration of the fan specifically regulate so that this critical area is traversed quickly and easily. The desired optimization of the speed control made it necessary, however, to verify the predictions of the purely theoretical vibration analysis by an experimental measurement of vibration in operation on site.

Vibration measurement on a large scale

The measurement of the torsional moment on the drive shaft was in a conventional manner by means of strain gauges (DMS) in a full bridge circuit. By application of strain gage rosette at an angle of 45 ° to the shaft axis, the measurement of pure torsion is ensured because it may eliminate any bending stress components automatically. For the transmission of the measuring signal from the rotating shaft Howden engineers have in Russia for the first time, a new modular radio-telemetry system - consisting of the signal processing and the transmission module including battery supply on the shaft and a stationary receiver and control unit outside of the shaft tunnel. One problem: Because the transmitter rotates, a part of the radio range by the powerful wave will always be shadowed themselves. To ensure uninterrupted transmission therefore had two receive antennas are provided offset by 180 ° opposite one another on the inside of the protective tube shaft. The telemetry receiver is designed and evaluates the two antenna signals independently in a way that continuous error-free measurements for the evaluation are available. Another requirement of the measuring system: The frequency analysis of the measured data using Fast Fourier Transform (FFT) requires a relatively high sampling rate - 2.000 Hz in this application - so that all relevant vibration components can be determined.

A transmission module - six sensors

The advantages of the employed in Howden fans Dx fully digital telemetry from the house CAEMAX technology are in addition to the interference-free transmission, especially in the ease of use. The system can be remotely controlled conveniently via the bi-directional radio link. The parameters can be set on the control panel of the receiver unit itself or via a connected PC. This requires no special software - Once done thanks to the integrated web server technology enables any Internet browser.
SCT with a transmitter module mixes the signals from up to six sensors - two strain gauge bridges or four strain gage half bridges, also electrical voltage and temperature signals - capture and transfer. In addition, the ambient temperature of the measuring point and the voltage of the power supply to check the charge status of the batteries. The sampling rate per channel and in total may be up to 5 kHz. The supply of the transmitter electronics (including the encoder supply) battery provides over several hours safe operation. Alternative is available for continuous operation also an inductive supply via a inductive head or a ring stator.
To play the transmitted signals are freely usable six analog outputs, and an Ethernet interface and a CAN interface for the digital transmission of the measured data. Here, all data is already converted and displayed as a physical quantity output. Using an SD memory card, the system can upgrade even as a small autonomous data logger.