Condition-Based Monitoring

The AD7768-1 is a low power, high performance, Σ-Δ analog-to-digital converter (ADC), with a Σ-Δ modulator and digital filter for precision conversion of both ac and dc signals. The AD7768-1 is a single-channel version of the AD7768, an 8-channel, simultaneously sampling, Σ-Δ ADC. The AD7768-1 provides a single configurable and reusable data acquisition (DAQ) footprint, which establishes a new industry standard in combined ac and dc performance and enables instrumentation and industrial system designers to design across multiple measurement variants for both isolated and nonisolated applications.

The AD7768-1 achieves a 108.5 dB dynamic range when using the low ripple, finite impulse response (FIR) digital filter at 256 kSPS, giving 110.8 kHz input bandwidth, combined with ±1.1 ppm integral nonlinearity (INL), ±30 µV offset error, and ±30 ppm gain error.

A wider bandwidth, up to 500 kHz Nyquist (filter −3 dB point of 204 kHz), is available using the sinc5 filter, enabling a view of signals over an extended range.

The AD7768-1 offers the user the flexibility to configure and optimize for input bandwidth vs. output data rate (ODR) and vs. power dissipation. The flexibility of the AD7768-1 allows dynamic analysis of a changing input signal, making the device particularly useful in general-purpose DAQ systems. The selection of one of three available power modes allows the designer to achieve required noise targets while minimizing power consumption. The design of the AD7768-1 is unique in that it becomes a reusable and flexible platform for low power dc and high performance ac measurement modules.

The AD7768-1 achieves the optimum balance of dc and ac performance with excellent power efficiency. The following three operating modes allow the user to trade off the input bandwidth vs. power budgets:

• Fast mode offers both a sinc filter with up to 256 kSPS and 52.2 kHz of bandwidth, and 26.4 mW of power consumption, or a FIR filter with up to 256 kSPS, 110.8 kHz of bandwidth and 36.8 mW of power consumption.
• Median mode offers a FIR filter with up to 128 kSPS, 55.4 kHz of bandwidth and 19.7 mW of power consumption.
• Low power mode offers a FIR filter with up to 32 kSPS, 13.85 kHz of bandwidth and 6.75 mW of power consumption.

The AD7768-1 offers extensive digital filtering capabilities that meet a wide range of system requirements. The filter options allow configuration for frequency domain measurements with tight gain error over frequency, linear phase response requirements (brick wall filter), a low latency path (sinc5 or sinc3) for use in control loop applications, and measuring dc inputs with the ability to configure the sinc3 filter to reject the line frequency of either 50 Hz or 60 Hz. All filters offer programmable decimation.

A 1.024 MHz sinc5 filter path exists for users seeking an even higher ODR than is achievable using the low ripple FIR filter. This path is quantization noise limited. Therefore, it is best suited for customers requiring minimum latency for control loops or implementing custom digital filtering on an external field programmable gate array (FPGA) or digital signal processor (DSP).

The filter options include the following:

• A low ripple FIR filter with a ±0.005 dB pass-band ripple to 102.4 kHz.
• A low latency sinc5 filter with up to a 1.024 MHz data rate to maximize control loop responsiveness.
• A low latency sinc3 filter that is fully programmable, with 50 Hz/60 Hz rejection capabilities.

When using the AD7768-1, embedded analog functionality within the AD7768-1 greatly reduces the design burden over the entire application range. The precharge buffer on each analog input decreases the analog input current compared to competing products, simplifying the task of an external amplifier to drive the analog input.

A full buffer input on the reference reduces the input current, providing a high impedance input for the external reference device or in buffering any reference sense resistor scenarios used in ratiometric measurements.

The device operates with a 5.0 V AVDD1 − AVSS supply, a 2.0 V to 5.0 V AVDD2 − AVSS supply, and a 1.8 V to 3.3 V IOVDD − DGND supply.

In low power mode, the AVDD1, AVDD2, and IOVDD supplies can run from a single 3.0 V rail.

The device requires an external reference. The absolute input reference (REF_IN) voltage range is 1 V to AVDD1 − AVSS.

The specified operating temperature range is −40°C to +125°C. The device is housed in a 4 mm × 5 mm, 28-lead LFCSP.

Note that, throughout this data sheet, multifunction pins, such as XTAL2/MCLK, are referred to either by the entire pin name or by a single function of the pin, for example, MCLK, when only that function is relevant.

Applications

• Platform ADC to serve a superset of measurements and sensor types
  • Sound and vibration, acoustic, and material science research and development
  • Control and hardware in loop verification
  • Condition monitoring for predictive maintenance
  • Electrical test and measurement
  • Audio testing and current and voltage measurement
  • Clinical electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (ECG) vital signs monitoring
  • USB-, PXI-, and Ethernet-based modular DAQ
  • Channel to channel isolated modular DAQ designs

The ADcmXL3021 is a complete vibration sensing system that combines high performance vibration sensing (using micro-electromechanical systems (MEMS) accelerometers) with a variety of signal processing functions to simplify the development of smart sensor nodes in condition-based monitoring (CBM) systems. The typical ultralow noise density (26 μg/√Hz) in the MEMS accelerometers supports excellent resolution. The wide bandwidth (dc to 10 kHz within 3 dB flatness) enables tracking of key vibration signatures on many machine platforms.

The signal processing includes high speed data sampling (220 kSPS), 4096 time sample record lengths, filtering, windowing, fast Fourier transform (FFT), user configurable spectral or time statistic alarms, and error flags. The serial peripheral interface (SPI) provides access to a register structure that contains the vibration data and a wide range of user configurable functions.

The ADcmXL3021 is available in a 23.7 mm × 27.0 mm × 12.4 mm aluminum package with four mounting flanges to support installation with standard machine screws. This package provides consistent mechanical coupling to the core sensors over a broad frequency range. The electrical interface is through a 14-pin connector on a 36 mm flexible cable, which enables a wide range of location and orientation options for system mating connectors.

The ADcmXL3021 requires only a single, 3.3 V power supply and supports an operating temperature range of −40°C to +105°C.

APPLICATIONS

• Vibration analysis
• CBM systems
• Machine health
• Instrumentation and diagnostics
• Safety shutoff sensing

The ADXL1001/ADXL1002 deliver ultralow noise density over an extended frequency range with two full-scale range options, and are optimized for industrial condition monitoring. The ADXL1001 (±100 g) and the ADXL1002 (±50 g) have typical noise densities of 30 μg/√Hz and 25 μg/√Hz, respectively. Both accelerometer devices have stable and repeatable sensitivity, which is immune to external shocks up to 10,000 g.

The ADXL1001/ADXL1002 have an integrated full electrostatic self test (ST) function and an overrange (OR) indicator that allow advanced system level features and are useful for embedded applications. With low power and single-supply operation of 3.3 V to 5.25 V, the ADXL1001/ADXL1002 also enable wireless sensing product design. The ADXL1001/ ADXL1002 are available in a 5 mm × 5 mm × 1.80 mm LFCSP package, and are rated for operation over a −40°C to +125°C temperature range.

Applications

• Condition monitoring
• Predictive maintenance
• Asset health
• Test and measurement
• Health usage monitoring system (HUMS)

The Wireless Vibration Monitoring Platform is a system evaluation solution for a wireless signal chain for MEMS-accelerometer based vibration monitoring. The system solution combines mechanical attach, hardware, firmware, and PC software to enable rapid deployment and evaluation of a three-axis vibration monitoring solution. The module can be directly attached to a motor or fixture, via a ¼-28 stud. It can also be combined with other modules on the same wireless mesh network to provide a broader picture with multiple sensor nodes, as part of a Condition Based Monitoring (CbM) system.

Solution Overview

The CbM hardware signal chain consists of a three-axis ADXL356 accelerometer mounted to the base of the module. The outputs of the ADXL356 are conditioned and converted to digital with three AD7685 16-bit daisy chain ADCs. The ADC outputs are buffered and transformed to the frequency domain in the ADuCM4050 low power microcontroller and from there streamed to the SmartMESH IP mote. From the SmartMESH chip time domain and FFT data are wirelessly streamed to the SmartMESH IP Manager. The manager connects to a PC and visualization and saving of the data can take place. Data is displayed as raw time-domain data, and FFT data. Additional summary statistics information on the time-aggregated data are available. The full Python code of the PC-side GUI, as well as the C firmware deployed to the module is made available to enable customer adaptation.

The evaluation kit consists of the following items:

• SmartMesh IP Manager (DC2274A) USB Dongle
• Wireless Vibration Monitoring Platform
• JTAG Cable (only needed for firmware upgrade)
• Programing board (only needed for firmware upgrade)