ADVERTISEMENT FEATURE COVER STORY A reference guide to correct accelerometer use


DJB Instruments is leading the way in providing specific accelerometer training and has created a guide to their use


TERMINOLOGY AND TYPES Piezoelectric – Charge Output devices, require a charge amplifier or an IEPE inline converter. Pros – Great for high temperature use - 260°C; purely mechanical assembly, robust and can withstand more severe environ- ments; wideband frequency response, 0.1Hz to 15kHz or more. Cons – Very sensitive to noise issues caused by dirt on connectors, cable type and length.


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n the 43 years it has been making accelerom- eters, DJB Instruments UK has seen many


changes in technology, analysis techniques and the increased reliance on test software. Although the applications for accelerometers has increased, the understanding of how they should be selected, mounted, connected and handled has reduced. Today many engineers see them as a simple sensor, however this is far from the truth. In the world of dynamic vibra- tion measurement, nothing is simple and errors of up to 35 per cent can be introduced before a single piece of data is analysed. It remains the responsibility of the engineer


to collect accurate data. Acquisition software on PCs cannot determine good data from bad, so the engineer must ensure accuracy starts at the sensor. For the last four years DJB has been leading the


way in providing specific accelerometer training to customers and this article summarises some key information for use as a reference guide.


6 2017-2018 | MEASUREMENT & SENSORS DIRECTORY


IEPE (Integrated Electronic Piezoelectric) – Also known by a variety of other names, but all refer to an electronic amplifier circuit built into the accelerometer. Pros – Signal conditioning built into many acquisition hardware systems, no need for a charge amplifier; less sensitive to cable type or noise effects; wideband frequency response, 0.1Hz to 15kHz or more. Cons – Lower temperature range, 125°C standard, 185°C High temperature; more sus- ceptible to damage due to electronic compo- nents; susceptible to ESD damage; fixed sensi- tivity and range.


MEMS (Micro Electromechanical System) – Piezoresistive or variable capacitance Pros – DC low frequency response Cons – Restricted temperature operating range; restricted frequency range (DC to 1kHz typical); sensitive to damage.


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