Sensor Technology RWT420, User Manual

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© Sensor Technology Ltd 2015 RWT3722R (Rev5)
When ordering a Torque Transducer please note that any torque/FSD is possible between ranges – please specify
rated torque and options using the following format:
For example: RWT
411 - 15Nm - K-CL
A ‘basic’ transducer with
torque and speed outputs,
rated and calibrated to
15Nm FSD with keyed ends,
±10v and IP65 protection.
Your transducer requirement:
RWT
Max speed (if applicable) RPM
Connector & Lead options (if applicable)
See over
Additional related products (if applicable)
See over
Glossary of terms and definitions used in this datasheet
 Surface Acoustic Wave (SAW) - An acoustic wave travelling along the surface of a material having some
elasticity, with amplitude that typically decays exponentially with the depth of the substrate.

Strain dependent SAW resonators
– A type of elastic SAW device, which changes its resonant properties
when it is subjected to axial strain/compression. TorqSense uses this principle, which is protected by a
number of patents.

Incremental Electronic Scan (IES)
– The most successful and precise method for interrogating strain
dependent SAW resonators. The IES interrogation method uses a processor controlled frequency synthesiser
to excite the SAW resonators over a defined range of frequencies and measure the reflected signal.
TorqSense uses this patented method.
 Resolution of the IES method - The minimum measurable number corresponding to the stress/strain
sensitive resonance point of the SAW resonator. The value is limited by following the factors:
 frequency resolution of the synthesiser, which is 1000 times greater then overall resolution of the
system.

relationship between frequency response and resolution. Increments of the resolution will proportionally
decrease the system’s frequency response. TorqSense systems are optimised for the best performance
that suits most applications. However, on the RWT420 series models customers do have the capability
to adjust the system performance.

Frequency response of the IES method
– The measure of the TorqSense system's response at the
output to a signal of varying frequency at its input. The frequency response is typically characterised by the
magnitude of the system's response, measured in dB. There are two ways of characterising the system’s
frequency response:
 0.1dB frequency range, where the output magnitude of the signal is different to the input magnitude of
the signal by not more then 0.1dB (practically absolutely identical).
 3dB frequency range, where the output magnitude of the signal is 0.707 of the input signal. This is a
common standard for most applications, unless it specifically says otherwise. This standard is also used
to characterise the TorqSense system’s frequency response.

Accuracy
- The degree of conformity of a measured or calculated quantity, which will show the same or
similar results. Accuracy of the overall TorqSense system is limited by the combined error of several factors
such as linearity, hysteresis, temperature drifts and other parameters affecting measurements. If errors in
the system are known or can be estimated, an overall error or uncertainty of measurement can be
calculated.

Digital averaging
– The application of algorithms to reduce white noise. In any electronic system,
electronic white noise is mixed with the signal and this noise usually limits the accuracy. To reduce the
influence of white noise and increase the accuracy of the system different averaging algorithms can be
applied. In the TorqSense system a flying digital averaging technique is applied to reduce the white noise
commensurate with the level of accuracy required. However, as any averaging algorithm works as a low
pass filter, the more averaging that is applied the lower the frequency response. Therefore, each Torqsense
system should be optimised to the customer’s requirements by choosing the right combination of
accuracy/frequency response. Please see relevant part of the Datasheet and User Manual.
Data parameters measured at +20°C
Sensor Technology Ltd reserves the right to change specification and dimensions without notice.