The noise performance of four low cost and one reference classic gyroscope is estimated using the Allan variance (AV). The purpose is to highlight problems connected with this process and to decide which parameters are the most important if we want to choose the best gyro for a particular application. From the AV theory, basic kinds of noise and their characteristic slopes of the AV curve are known. For example, angle random walk has the slope of -1/2 and is caused by the white noise on the gyro output. However, the output of low cost gyro is usually corrupted by the more or less correlated noise. The level of correlation affects the slope of AV curve, so the better sensor has the slope closer to the theoretical value, thus a simpler model can be used. When collecting data for analysis, it is the most important to suppress temperature variations and vibrations. Attention should be paid to choose proper sampling frequency. Also the resolution and the connection of an acquisition card should be considered.

This paper presents a simple method for compensating the Sagnac phase shift in an interferometric fiber-optic gyroscope (I-FOG) with a piezoelectric modulator. The common advantages of I-FOGs with closed-loop compensation are linearized output characteristics and insensitivity to the light source power, including its time and thermal-induced fluctuations. Whereas closed-loop operation is normally achieved via ramp modulation requiring an electro-optic modulator, all-fiber architectures with a piezoelectric modulator are mostly limited to open loop. Nevertheless, such setups can more conveniently utilize a less expensive single-mode fiber with depolarized light and do not require any custom-made components. The proposed method allows us to combine the advantages of both approaches. Closed-loop compensation is ensured by adding further sinusoidal modulation to the common biasing modulation, such that the Sagnac phase shift is compensated solely at the sampling instants. We describe and experimentally demonstrate the proposed approach, utilizing a test setup to compare our closed-loop solution with open-loop operation. The results denote that the method provides a cost-efficient manner of performance improvement compared to the open-loop I-FOGs based on a piezoelectric modulator.

A novel and simple way of improving the mean wavelength temperature stability of the erbium-doped superfluorescent source is described and demonstrated. We show that by introducing small reflectivity feedback at the unpumped fiber end in the backward-pump superfluorescent source configuration, we can affect an overall temperature dependency of the mean wavelength of the output spectrum. The reflectivity adjustment can be made by an angled fiber cleave, varying the reflectivity between 0 to 4 %, or by a fusion arc, allowing its finer adjustment. With this approach, we were able to arbitrarily adjust the mean wavelength temperature trend from -4.38 to 5.23 ppm/ $^{\circ }$ C. Furthermore, an optimal reflectivity was attained, providing almost zero trend and reducing the total mean wavelength variation to 130 ppm over the temperature range of -40 to +100 $^{\circ }$ C, which is a 5.7-fold and 4.4-fold improvement compared to 0 $^{\circ }$ and a standard 8 $^{\circ }$ fiber cleave angle, respectively. By avoiding any filtering components, a wide bandwidth of 37.8 nm and a power efficiency of 22% was reached. Since the proposed configuration does not include any extra components compared to the basic backward-pump configuration, it can be a viable solution for cost-efficient applications, such as, e.g., medium-grade fiber-optic gyroscopes. A benefit for these gyroscopes is the tunability of the source wavelength temperature dependency which can conveniently compensate the gyro coil temperature sensitivity.

Measuring the efficiency of piezo energy harvesters (PEHs) according to the definition constitutes a challenging task. The power consumption is often established in a simplified manner, by ignoring the mechanical losses and focusing exclusively on the mechanical power of the PEH. Generally, the input power is calculated from the PEH’s parameters. To improve the procedure, we have designed a method exploiting a measurement system that can directly establish the definition-based efficiency for different vibration amplitudes, frequencies, and resistance loads. Importantly, the parameters of the PEH need not be known. The input power is determined from the vibration source; therefore, the method is suitable for comparing different types of PEHs. The novel system exhibits a combined absolute uncertainty of less than 0.5% and allows quantifying the losses. The approach was tested with two commercially available PEHs, namely, a lead zirconate titanate (PZT) MIDE PPA-1011 and a polyvinylidene fluoride (PVDF) TE LDTM-028K. To facilitate comparison with the proposed efficiency, we calculated and measured the quantity also by using one of the standard options (simplified efficiency). The standard concept yields higher values, especially in PVDFs. The difference arises from the device’s low stiffness, which produces high displacement that is proportional to the losses. Simultaneously, the insufficient stiffness markedly reduces the PEH’s mechanical power. This effect cannot be detected via the standard techniques. We identified the main sources of loss in the damping of the movement by the surrounding air and thermal losses. The latter source is caused by internal and interlayer friction.

This article describes an open multimodal dataset acquired during controlled run-to-failure tests of 54 deep-groove ball bearings. A purpose-built test bench comprises five independently driven loaded stations and records vibration acceleration, acoustic emission, bearing temperature, static radial load, motor torque, rotational speed, and ISO vibration velocity. The current experiments use type 608 bearings from four anonymized manufacturers at a nominal speed of 6000 1/min and a radial load of 1.4-1.7 kN. Vibration acceleration is sampled at 51.2 kS/s and stored as a 10 s segment once per minute together with process variables. Acoustic emission is sampled at 5 MS/s in the 50–250 kHz band; continuous signal parameters and threshold-triggered hit descriptors are stored, with three predefined hit thresholds set to 125%, 150%, and 200% of the running RMS. The repository contains separate vibration and acoustic-emission folders for each tested bearing, raw TDMS files containing vibration signals, process variables and metadata describing the channels, text files containing continuous AE signal parameters and threshold-triggered hit descriptors, and a text file containing general information about the test. The captured data support studies of degradation trajectories, early fault detection, health-index construction, remaining-useful-life estimation, possible multimodal data fusion, sensor selection, and comparisons of diagnostic and prognostic algorithms.