Strain Gauge Technology Enhances LVDT Sensors

Applied Measurements is now able to provide AML-SGD products with the ability to measure linear displacement over an extended range. With the existing AML-SGD products starting as low as 0-5mm and measuring up to 50mm over four models, the latest introduction measuring 0-100mm is the result of increased demand from customers preferring to use a strain-gauge-based measuring system.

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 temperature stability, according to the company. The characteristics of strain-gauge-based sensors provide higher accuracy linear sensing than that of lower-resolution LVDT sensors. 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.

These 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 more attractive to a user. Additionally, strain-gauge-based displacement transducers exhibit typical non-linearity errors of a quarter of that of typical LVDTs. As with other strain gauge devices, the resolution is infinite and strain sensitivity is constant with a stabilised input voltage between 1.5V DC and 15V DC. 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 less than +/-0.1 per cent. 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 mechanical reliability, hence the three-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 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 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. 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 displacement sensors are used by industries such as RandD, machine builders, automotive, marine and geotechnical.


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