This application guide is designed to help developers understand the unique function of the KX13x series of three-axis acceleration sensors from Kionix, a subsidiary of the ROHM Group-Advanced Data Path (ADP). ADP consists of a user-customizable frequency filter and a root mean square (RMS) calculator, which provides the acceleration amplitude within the required bandwidth.

1 Introduction

This application guide is designed to help developers understand the unique function of the KX13x series of three-axis acceleration sensors from Kionix, a subsidiary of the ROHM Group-Advanced Data Path (ADP). ADP consists of a user-customizable frequency filter and a root mean square (RMS) calculator, which provides the acceleration amplitude within the required bandwidth. The 16-bit ADP output of the X, Y and Z axis can be read from the dedicated output register, stored in the 512-byte FIFO buffer, and then routed to Wake-Up and Back-to-Sleep (return to sleep) engine. By setting the desired threshold amplitude and counter value, an interruption can be generated for a specific movement, rotation or vibration. This article will introduce two simple examples to visually demonstrate the advantages of this new feature.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 1: Schematic diagram of the advanced data path (ADP) principle

Acceleration information in the real world (left) is a mixture of different frequencies and amplitudes. KX13x’s ADP can not only capture this information, but also output acceleration amplitudes within a specified frequency range (examples of various situations are listed on the right).

2. Data flow

Figure 2 shows a general data flow diagram. The first box at the top of the figure is the Conventional Data Path (CDP) of the digital accelerometer. CDP includes analog input from MEMS, an analog front end (AFE) responsible for amplifying the signal, an analog-to-digital converter (ADC) responsible for signal digitization, and a digital signal processing (DSP) unit responsible for further processing. The Advanced Data Path (ADP) contains a pair of highly configurable digital filters-a combination of low-pass and high-pass filters, and a root mean square (RMS) calculator that calculates real-time amplitude. Users can flexibly access and set the ADP filter. The filter can be set as Butterworth, Bessel, Chebyshev filter, and even configured as a custom filter. The output of ADP can be stored in a dedicated output register, it can also be routed to the built-in 512-byte FIFO buffer, or it can be implemented in two ways at the same time. In addition, the ADP output can be routed as an input to the built-in action Wake-Up and Back-to-Sleep engines. These engines can be configured with thresholds and flexible counters to further limit the signal. If the input signal criterion is met, the interrupt generator in the device will generate a physical interrupt for the host and set the corresponding status register. Figure 2 shows that when it detects “continued ThAn example situation where an interruption occurs when a specific vibration of time” occurs.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 2: ADP data flow

3. Application examples

3.1. Machine health

Suppose fopIs the working frequency of the mechanical system (such as a rotating electric machine), feIs the error/failure mode frequency of the system (Figure 3). In this example, feLess than fopAnd it is shown in this figure that the motor is slowly vibrating due to the looseness of the body. For traditional acceleration sensors, in order to detect this failure mode, people need to use MCU/DSP for frequency analysis. The MCU/DSP keeps working all the time, which will lead to additional memory space requirements and higher power consumption.

The KX13x’s ADP can detect such events only by using an acceleration sensor, and if the ADP digital filter is set to a band-pass or low-pass filter, let fePass to eliminate fop, It can also generate interrupts for the host MCU.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 3: Frequency analysis of normal system actions and faulty system actions

In Figure 4, please note that the ADP is configured as a low-pass filter to eliminate fop, and the RMS calculation engine is configured to obtain the absolute value of the desired failure mode signal. The signal threshold (intermediate waveform) in the action engine is used to qualify the event. Finally, the waveform at the bottom of the figure shows the real signal generated by the motion engine. After detecting a fault event, the WUFS bit in the INS3 register will be set, and the external interrupt pin (if configured) will generate an interrupt signal.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 4: ADP separates the target signal from the original acceleration data and passes the amplitude information to the motion engine

3.2. Envelope analysis

Envelope analysis is an effective method to detect periodic vibration faults, such as anti-friction bearing failures. ADP can be used to generate the envelope of acceleration data (* 1). The fast Fourier transform (FFT) of the envelope waveform can show the period of vibration, which helps to identify defective parts in the system. In this example, the ADP filter should be configured as a “band pass”: both vibration frequency and error frequency are included, and DC noise and high frequency noise are excluded.

(*1) Note: ADP output is a pseudo-envelope, not the result of Hilbert transform.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 5: Periodic vibration caused by a bearing ball failure

The envelope waveform can be stored in the 512-byte buffer of the KX13x or sent to the host processor for FFT analysis.

Introduction to the advanced data path function of Kionix three-axis accelerometer
Figure 6: FFT using raw acceleration data and its envelope

For more detailed information and usage of KX13x ADP, please contact ROHM sales representatives.

The Links:   2MBI400TC-060-01 4R3TI60Y-080