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Product category: Loadcells, Force Sensors and Torque Sensors
News Release from: Datum Electronics | Subject: Series 420 torque transducers
Edited by the Engineeringtalk Editorial Team on 07 March 2008

Torque measurement aids machine
efficiency

Improved torque measurement capabilities on rotating machinery will provide great benefits to the many modern industries, claims Nick Cross of Datum Electronics.

Torque and strain measurement techniques are widely used and understood in many industries; but new developments in signal processing and transmission have greatly enhanced our torque transducers' capability and worth Our torque transducers can now be supplied into systems able to provide more information than we knew could be available as little as 5 years ago

Able to fit applications that demand ever smaller and more environmentally demanding space, combined with the latest in technology and design, Datum Electronics is providing the torque transducers of the future for the industries of the future.

As an extension to the basic range of torque measurement products, Datum Electronics has the capability to prepare specialist measurement systems to assist with the analysis of dynamic torque in a wide range of applications.

Our capabilities include the ability to measure high frequency "torsional" changes within a transmission system.

These changes will show torsional vibration - out of balance and unwanted drive vibration components; torsional ripple - gear meshing, blade cycling, offset loading; and dynamic events - gear changes, braking and acceleration.

We can configure measurements to be taken to look at events up to 15kHz in burst mode and 5kHz in a continuous mode.

The system will allow the selective measurement of small fluctuations as low as 1:10,000 of the full shaft torque range.

The data can be made available in graphical, analogue or digital formats.

Datum Electronics can advise on the optimum system to collect the data from your transmission line, and with the analysis of the data.

For example, in order to monitor the meshing of the teeth within gearboxes a requirement existed to measure the average drive torque through the test cycle and to control the test rig.

Most standard torque transducers would accomplish this.

However a second set of instrumentation was also required to measure and monitor the meshing of the gear teeth.

The shaft in this case was operating at 6000rev/min and the primary gear had 30 teeth giving a meshing frequency of 3000 teeth per second.

With standard transducer sampling at between 100Hz and 3kHz it would supply insufficient data for analysis.

Using cutting edge technology, we developed a new torque transducer with a high sampling rate that could look at the torque on the input and output shafts providing both an average torque signal for control and bursts of high-speed "ripple" gear meshing data.

This torque transducer provided average torque with a control update at 50Hz with feedback to the test rig drive.

However, the burst mode provided 30,000 samples per second for 2 seconds to look at the meshing torque.

The burst of data was timed every 30 minutes providing 60,000 samples for analysis.

The specially developed Datum Electronics software used to collect the data on the PC was able to package the high quantity of data suitable for use direct into an Excel spreadsheet.

The same family of Series 420 torque transducers has also been used to provide data on torque events such as turbine braking where the burst mode was triggered to provide 1 second of data (ie 60,000 samples) to plot the transient torque.

Enhancements such as these added to standard monitoring and control transducers will enable any company with service and design personnel to gather more specialist data from standard equipment completing every day functions.

Another example is in testing the energy transmitted through a gearbox at specific frequency bands.

The torsional vibration on a transmission line contains many frequencies.

It is not uncommon that other higher magnitude vibrations at different frequencies mask the frequency at which measurements are required.

The magnitude at the frequencies to be measured was minute at 0.02% of the full shaft torque.

A specialist torque module was developed that was able to look at both the underlying torque level and the fluctuation within that level.

The transducers were designed to transmit a data stream that could be separated giving two channels or components required.

The configuration of the transducer allows for multilevel filtering of the raw signal to remove any dominant unwanted areas and isolate the required or problem frequency.

The transmitted conditioned signal was provided as two 4-20mA outputs, the control channel giving 4-20mA for 0-2000Nm and the analysis channel giving 4-10mA for 0.4Nm (fluctuation).

A bandpass filter in the analysis channel isolated at a key meshing frequency of 350Hz +/-50Hz.

Our ability to add features of this type to torque transducers and power meters will enable engineers to diagnose and monitor a much wider range of parameters on their system.

A good example is the wind energy business, with suitable configuration of gearbox frequencies and propeller frequencies will be related to items such as bearing failure, shaft whirling and propeller cavitation.

With remote monitoring using this technology, the possibilities are exciting and boundless.

Real and accurate monitoring of remote systems means problems can be spotted quickly and dealt with, well before it becomes a critical problem.

A third example is in measuring torque underwater on a shaft, with both radial and lateral oscillation.

The problem in this instance was large shaft movement in relation to any local fixed position around it.

As with any submersible device the use of bearings was to be avoided.

The torque on the driven shaft was to be measured over a large dynamic range with particular interest at very low levels, therefore the drag of any rubber seal, bearing assembly or similar restriction was undesirable.

For some time, our 420 Series torque transducers which are required for long running tests have been manufactured with a completely separate rotor and stator assemblies.

These are able to operate with visible air gaps of up to +/-7mm between the rotor shaft and the stator.

A solution to the subsea problem was relatively simple by producing a marine version the standard assembly that could be used on conventional ship shafts and increased power storage capability on the rotor to allow the transducer to operate outside its normal inductive power envelope.

This solution allowed continuous transmission of average power transmitted even in heavy sea conditions where the rotor could not be fully constrained.

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