Tuesday, July 31, 2012

LVDTs well suited to capture high speed and high frequency movement

Due to their fundamental design and mode of operation LVDT's are very suitable for measuring high speed and high frequency movements on mechanical structures.

Applications calling for high frequency movements include switch testing, recoil testing, blast testing and high frequency component testing. It is important not to confuse sample rate with frequency response. The parameter being measured is the analogue frequency response, so that, for example, a mechanical oscillation of 500 repetitions per second would be faithfully reproduced by the LVDT output. A typical RDP LVDT and amplifier combination can have a mechanical frequency response of up to 500 Hz. Where applications need to go faster, this can be enabled by modifications to the signal conditioning electronics.

LVDTs are available in ‘spring return’, ‘guided’ and ‘unguided’ mechanical configurations which determine the LVDT frequency response. A spring return type is limited by the ratio of the mass of the amplifier compared to the strength of the spring which typically on a short transducer imposes a limit of the order of 10 Hz. A captive type transducer is not restricted in this way but since it contains guidance bearings if exposed to multi-millions of cycles, will eventually show signs of wear. Consequently the preferred transducer configuration to use for high frequency applications is the unguided type. This version can be arranged to make physical contact between the armature and the body of the transducer and so can operate indefinitely at high frequencies.

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