March/April 2020

| SOLUTIONS | www.smartmachinesandfactories.com March/April 2020 | 29 | with higher levels of integration to allow system builders to make this increased sensing future a reality now. Data acquisition To achieve the earliest possible indication of machine wear-out, you almost need to see into the future. In the realm of condition monitoring analytics, this is achieved by looking for the minutest changes in the system, whether it be system temperature, vibration, or acoustic signature. To sense these small changes requires sensors and data acquisition systems that can see the small changes clearly at the lowest detection levels, even amongst high levels of vibration or temperature. This requires signal chains with extremely high dynamic range, meaning systems with extremely low noise performance while still being able to deal with large variations in signal level. For example, to detect the onset of wear-out in a reciprocating pump may require the detection of a change in less than 1/10th of a mm of the end stroke position of the piston, where the piston is moving up to 300 mm overall. To ensure that we can see this change, the system noise must be below this by at least a factor of 10. This pushes the detection level to 1:300,000, or 109 dB, and requires 18-bit or more accurate data acquisition systems. Another consideration is the need to push out of the bandwidth of interest. Motor axles and many gear systems have characteristic vibrations at relatively low frequencies, with frequencies at close to the rotation speed of the axle or low multiples of this. However, there are other components in the systems that have higher frequency features. To detect shifts in the wear of components that have higher frequency characteristics, such as ball and oil bearings, the sensing must be able to achieve high resolution and high dynamic range at frequencies beyond 10 kHz and up to 80 kHz. The sensing system specifications must include high dynamic range (DR), as well as extremely low total harmonic distortion (THD) in order to resolve these frequency domain features in the system vibration profile. In these systems, the latest precision wide bandwidth sigma-delta (?-?) converters are used to perform the analog-to-digital conversion step. There are extremely accurate analog- to-digital converters that meet the key requirements for these systems. Converters in this category are specified with superior dynamic range and THD (typically +108 dB DR and ?120 dB THD), which is achieved across a bandwidth of dc to at least 80 kHz, combined with ease-of-use features such as analog input pre- charge buffers, integrated digital filters, and cross-device synchronization for multichannel phase matching, make these key components in the building of the highest performance CbM data acquisition systems. Power scaling features allow the same physical hardware to be tuned to meet specific power ceilings, where dynamic range or bandwidth can be traded-off against total power. And providing accuracy at dc as well as wider bandwidth allows the input channels to address the needs of temperature, strain, and other dc or low bandwidth sensing in the same platform, which simplifies the overall condition monitoring system architecture and complexity—a single platform for all CbM sensor types. Simultaneous Sampling In CbM systems, simultaneous sampling is used to ensure the phase relationships between sets of time domain data is preserved. For example, where two orthogonally arranged vibration sensors are used, this allows the direction and amplitude of the vibration phasors to be detected. Ideally the phase delays through each sensor input path should be well matched and track over temperature. For CbM systems that require even more flexibility in their design for wider range in their sampling rate, bandwidth, or power scaling needs, SAR ADC products are also appropriate. These devices also offer high dynamic range and THD, and at throughputs up to 2 MSPS, and also incorporate ease of use features that reduce signal chain power consumption, reduce signal chain complexity, and enable higher channel density. Converters with higher input impedance modes broaden the range of low power precision amplifiers that can drive these ADCs directly, while still achieving optimum performance. To allow system builders to achieve the highest possible channel densities in more compact or distributed acquisition nodes, and to achieve faster time to market, signal chain ?Module products with higher levels of integration than ever before are being developed. These ?Module devices combine key components commonly used in data acquisition signal chain designs within a compact, integrated circuit (IC)-like form factor. The ?Module approach transfers the design burden of analog and mixed- signal component selection, optimization, and layout from designer to device, which shortens the overall design time and system troubleshooting, as well as ultimately improves time to market. Housed in tiny packages, ?Module devices are well suited to distributed low channel count, compact CbM systems or for higher channel count rack-based systems. Sensors Providing high dynamic range, wider bandwidths, greater power efficiency, and higher channel densities in the data acquisition part of the signal chain alone only addresses part of the system design challenge for CbM systems. Traditional integrated electronics piezoelectric (IEPE) vibration sensors are large, bulky, and expensive, and are usually run off relatively much higher voltage rails than the data acquisition system. Common piezoelectric sensors use a ?24 V single supply, consuming upward of 2 mA, and are housed in heavy metal cases. Because the sensor supplies are usually provided by the data acquisition module, increasing the channel density in the box becomes a power density problem and a component density problem. Adding to this the need for wireless battery- powered acquisition nodes, the traditional piezo vibration sensor no longer meets the demands of these signal chains. MEMS vibration and inertial sensors are now meeting the requirements of these systems. The latest wide