High Accuracy Displacement Sensors Use Strain Gauge Technology

AML/SGD-100mm Strain Gauge Displacement TransducerAs a result of increased demand from customers preferring to use a strain gauge based measuring system, we have introduced a 0–100mm version to our range of AML/SGD high accuracy displacement transducers.

Based on a four-arm Wheatstone-Bridge design with a nominal impedance of 350 Ohms, the design ensures excellent non-linearity, low power consumption and excellent temperature stability.  Additionally, the characteristics of strain gauge based sensors provide higher accuracy linear sensing than that of less accurate and lower resolution LVDT sensors.

These advantages of our AML/SGD high accuracy displacement sensors have been realised by Oxfordshire based company Fugro GeoConsulting Limited, who use the existing 0-50mm version of the sensors within their accredited geotechnical soil-testing laboratory.  This high-tech establishment tests soil samples in order to predict how they will behave when subject to the stresses and loads that planned new buildings will place on them. The lab has worked on many major projects including some of the world’s tallest buildings, biggest bridges and countless oil & gas rigs and wind turbine sites. The loads being simulated in the lab include the varying effects of wind, wave, tide and earthquake action, as well as the dead weight of the building itself.  The sensors are used (together with submersible load cells, also from Applied Measurements) to accurately monitor small changes in the dimensions of the samples as tests progress.

Fugro’s Laboratory Manager, Roger Brown, said “We test soil samples from all over the world and considerable time and effort is spent retrieving them from varied and often challenging locations, for example from the seabed at deep water locations in the Atlantic Ocean and as such, each sample is unique and expensive to collect.  In addition, some tests can take several weeks to perform.  The lab gets one shot only at each test and hence we need confidence in the testing equipment so that the results can be relied upon”.  Because these sensors operate at similar voltage levels and produce output signals compatible with other commonly used strain gauge sensors such as load cells and pressure transducers, they can easily form part of the same measurement chain in one central instrumentation system.

The AML/SGD high accuracy displacement sensors operate on low cost DC strain indicators or digital voltmeters, whereas standard LVDT transducers require conversion of the signals to achieve the same level of compatibility.  The simplicity of this type of measurement requiring no further processing of the basic signal, can make this type of test or measurement significantly more attractive to a user.

Additionally, strain gauge based displacement transducers exhibit typical non-linearity errors of a quarter of that of typical LVDT’s.  As with other strain gauge devices, the resolution is infinite and strain sensitivity is constant with a stabilized input voltage between 1.5Vdc and 15Vdc.

The range of AML-SGD displacement sensors are precision assemblies contained within a rugged stainless steel outer casing. The internal construction of the AML/SGD transducer ensures a smooth, virtually frictionless movement of the inner core, resulting in high overall accuracy of <±0.1% on 0-5mm, 0-10mm and 0-25mm models, <±0.15% on the 0-50mm model and <±0.25% on the 0-100mm model.

The return force of the spindle is maintained at a minimum level for effective operation when installed upside-down, without having to attach the spindle to the subject.  This makes the sensor less intrusive to the application when measuring on soft or pliable materials.  The sensors are designed for long life and excellent mechanical reliability, hence the 3-year manufacturing warranty offered.  This is evidenced by existing applications where these transducers have passed 14 million cycles in normal operation.  And unlike some LVDT transducers, the AML/SGD product is completely serviceable by the manufacturer in the event of damage in use.

Any transducer device would be quite useless without means of providing appropriate supply voltage and output signal and this is often a significant part of any data acquisition programme.  The AML/SGD range of high accuracy displacement sensors ensure these costs remain at a minimum, by utilising strain gauge signal inputs of existing data acquisition equipment.  In this way, these displacement sensors limit expenditure to the cost of the sensor only, thus eliminating further capital outlay on dedicated instrumentation.

However these advantages would be of no use if this combination of user benefits meant extended lead times.  As such it is the policy of Applied Measurements to keep most standard ranges in stock, meaning that the payback period is shorter and the benefits can be realised sooner.

Compact, rugged and easy-to-install, AML/SGD high accuracy displacement transducers are used by industries such as R&D, machine builders, automotive, marine and geotechnical.  The total cost of ownership of instrumentation is now more relevant than ever for these industries and improvements in the versatility of sensors that allow their use with simple DC signal conditioning is but one method of spreading the life costs.

For more information on the range of AML/SGD range of high accuracy displacement transducers please see the AML/SGD Product Page or PDF Datasheet.  Alternatively, please call us 0118 981 7339 or send an email to: [email protected]