SAW Technology

Benefits & Competing Technologies

Read further about the benefits of SAW Sensor Technology and how it compares to competing technologies

Preserve System Integrity: Unlike other force and torque sensors, SAW technology measures microstrain, enabling measurement without compromising the mechanical integrity of the system. Simplifying the measurement of existing components.
Higher Measurement Accuracy: SAW torque sensors can deliver better than 1% of full-scale accuracy over the temperature range -40°C to +150°C together with low hysteresis and drift. Enabling improved control and performance.
High Speed Sensing: High sample rate of 2 kHz enabling for example, torque measurement in engines and powertrains every few degrees of shaft or disk rotation (eg. every 3 degrees at 1000 rpm).
Insensitive to Magnetic Fields: Many automotive applications require torque sensing close to electric motors and solenoids. This is problematic for some other types of sensor technology.
Measure moving components: Measures torque, thrust, pressure and temperature on rotating or moving components.
No wear and tear: Non-contact offers long mechanical life and are maintenance free as they don’t use parts which will wear and tear.
Wireless: There are no wires or slip rings between the sensor and electronics.
Passive: No electrical power is applied to or generated by the sensor, the energy exciting the SAW sensor is provided by the interrogating RF pulse.
Cost-effective: A typical Transense SAW sensor is an intrinsically a low cost device. It contains no electronic components.
Low Mass: A typical SAW sensor weighs less than 1 gram. This is very beneficial in motorsport applications where every gram counts
Small Size: Enables the addition of one or two sensing elements to existing components such as shafts or disks with only minimal intrusion or modification.
No special materials are required: Unlike other technologies the SAW torque sensor can be mounted on any type of steel even other types of metal.
Mechanically Rugged: SAW sensors have demonstrated considerable tolerance to high shock loads, high speed centripetal forces, vibration and chemical resistance.

Measurement of Surface Strain (Strain Gauge Sensors)

This has been the conventional method for measuring rotating torque by using a piezoresistive (a material that changes resistivity depending on strain) strain gauge attached to the rotating shaft. Changes in strain, because of torque, are recorded as variations in an electric signal.

Disadvantages

Reliance on torsional strain inhibits their application to shafts of arbitrary torsional stiffness, and to offer a frequency response above 1kHz
Strains are too small (at most a few parts of 1000) to be measured directly, so complicated workarounds must be established: conventionally, four gauges are arranged in a Wheatstone bridge circuit
Slip rings or local telemetry are required to feed a continuous current to the gauges and acquire the signal from the bridge circuit. The use of slip rings can act to limit the maximum RPM of the shaft, and wear can significantly reduce system reliability. The use of local wireless telemetry can limit the maximum bandwidth of the system and can either be prone to signal drop-out or create significant electromagnetic emissions that may interfere with other sensors, electronics, and telemetry on the vehicle.
Strain Gauges sensors are typically not robust or resilient to harsh environments

Measurement of the Twist Angle (Displacement Sensors)

This method typically uses a pair of identical toothed disks attached at opposite ends of a portion of the shaft enables a ‘twist angle’ to be determined from the phase difference between them through an optical or magnetic measurement, which in turn enables torque to be calculated.

Disadvantages

Requires the shaft to be rotating
Requires a reduced diameter section of the shaft known as a torsion bar to enhance the twist angle (several degrees at most for a length-to-diameter ratio L/D = 5)
Sensitive to temperature

Measurement of Magnetic Fields (Magnetoelastic/Magnetostrictive Sensors)

This method for torque readings is achieved through the measurement of changes in magnetic permeability or the magnetic field that occur on regions of the shaft surface because of torsional stress from the applied torque. These variations in permeability or the generated magnetic field are measured by encircling the shaft in some pattern of coils of wires and observing differences in induced voltages.

Disadvantages

Permeability does not depend exclusively on torque and will vary with frequency, temperature, and magnetization
The magnetostrictive effect is highly non-linear
Local variations in magnetic properties of typical shaft surfaces limit the attainable accuracy
Calibrated electronics are specific to each calibrated shaft and sensitive to variations of the gap between the shaft and pickup coils
Impact to the shaft can disrupt the magnetic properties on which the calibration is based.
Technology limited to the instrumentation of components manufactured from steel
Susceptible to the influence of stray magnetic fields (i.e. close proximity of motors)

	Strain Gauge Sensors	SAW SensorsSAW Sensors	Displacement Sensors	Magnetoelastic/ Magnetostrictive Sensors
Non-contact	NO ₁	YES	YES	YES
Torsionally stiff	NO	YES	NO	YES
Independent of T without need for compensation	NO	NO	In some cases	NO
Radially Mountable	NO	NO	YES	NO
Package-able in motorsport race conditions	NO	YES	NO	YES
Suitable for use is liquid environments i.e. oil	NO	YES	NO	NO
Frequency response	1kHz	Possible up to 8Kz, normally 1.7 kHz	500 Hz	2 kHz
Operational Speeds	NK ₂	0 – 30,000 rpm	NK ₂	0 - 20,000 rpm
Operational Temperature range	NK ₂	-40°C to+150°C	NK ₂	+20°C to +130°C
Static and Dynamic measurement	NO	YES	NO	YES
Suitable for medium to high volume manufacture	NO	YES	YES	NO
Suitability to a variety of steels and non-ferrite materials	YES	YES	YES	NO

1 - To have a non-contact capability requires inductive coupling, slips rings or electronic shaft telemetry
2 - NK = Not Known

SAW Technology

Technical Papers & Patents

Get an insight into the patented technology we develop through our technical publications

FAQ's

Questions and answers on our patented Transense Torque and Temperature sensors