Zoran Stare

Digital Measuring System for Monitoring Motor Shaft Parameters on Ships

The robust measuring system for the continuous monitoring of the ship motor shaft average torque, power, and rotational speed was developed and tested. The system was designed for permanent installation in ships under realistic working conditions. The strain gage sensor is employed to measure the torque, whereas the shaft rotational speed is measured by the inductive proximity switch. The strain gage signal conditioning circuit design was highly simplified by using a high-resolution SigmaDelta A/D converter (ADC). Such an approach minimizes the overall number of analog components and the input measuring chain errors. A contactless power transmission subsystem was developed based on the specifically designed rotary transformer operating at low frequency. Strain measurement results are transmitted over the near-field low-frequency capacitive link by using a specifically designed communication protocol based on the digital modulation principle. The receiver microprocessor-based unit processes the measured data and transmits the results to the monitoring human-machine interface over some commonly used industrial analog and digital communication protocols. The principal advantages of the novel measuring system design over some state-of-the-art commercial solutions are simplicity, higher accuracy, stability, reliability, simplified calibration procedure, and contactless signal transmission and processing completely in a digital form, which, hence, reduces the most common shortcomings of similar analog-based systems.

Low-frequency dielectric properties of the oral mucosa

Low-frequency (≤ 1 MHz) electrical conductivity and permittivity spectra of the oral mucosa were reconstructed from impedance measurements at various regions (tongue, buccal mucosa, hard palate) of the oral cavity. Impedance magnitude and phase were measured with the HP4284A LCR meter in the frequency range from 30 Hz to 1 MHz. Bipolar intraoral measurement probe was used. In order to obtain conductivity and permittivity spectra from measured impedance data, the geometry factor of the probe (cell factor) was determined theoretically. Namely, numerical modeling using the finite-element method was used to calculate the geometry factor. The FEM model was also used to study the sensitivity field of the probe and the penetration depth. The results show typical dispersion characteristics observed in α-, and β-dispersion range of biological tissues. Possibilities of correcting electrode polarization, which causes error at lower frequencies are considered.

Portable wireless measuring system for monitoring motor shaft parameters

A prototype of a portable wireless measuring system for monitoring motor shaft torque, power and rotational speed was developed and tested. The system was designed to offer great flexibility for a wide variety of test and research applications as well as having broad monitoring parameter ranges. Strain gauge sensors, placed onto the revolving shaft along with a wireless radio-frequency transmitter, are employed to measure torque. Shaft rotational speed is measured by using a rotary encoder. Torque and power are calculated automatically on the receiver side from samples processed in real time and displayed to the user. Moreover, the system provides analog and digital outputs of the shaft vibration waveform for oscilloscope observation or recording on a personal computer in a digital format.

Verification of physical models used for root canal measurement by impedance comparison

In the endodontic treatment of the root canal, one of the most important procedures is the root canal length determination. Apex-locators are commercial electronic de- vices used to determine canal length by measuring the electri- cal impedance. The verification of such instruments in-vivo is hard to perform because the only accurate way of measure- ment is by extracting the tooth and then measuring the canal length. For this reason, testing of apex-locators and their com- parison as well as new measuring method evaluation are often performed by model-based in-vitro measurements on extracted teeth. In this paper we demonstrate that significant differences between electrical properties of the model and the vital tooth exist. Frequently used physical models in current studies con- sist of a tooth immersed either in saline solution or in freshly mixed alginate. In order to investigate the electrical properties of these physical models, we have measured the value of root canal impedance |Z| and the elements of two-element parallel equivalent circuit (Rp, Cp) in both physical models and com- pared the results with in-vivo root canal impedance measure- ments. We have shown that the results of the measurements of electrical impedance on the physical models significantly differ from in-vivo measurements. Therefore, due caution is required when drawing conclusions about apex-locator accuracy or performing method evaluation based on model measurements.

Benefits and disadvantages of impedance-ratio measuring method in new generation of apex-locators

One of the most critical procedures for a successful endodontic treatment is determination of root canal length. Electronic devices called apex-locators have been used for working length measurement for more than forty years. First apex-locators used direct current, but had many drawbacks. In order to improve the measurement procedure, direct current was replaced by alternating current and impedance was measured on single frequency in order to calculate the position of apical constriction. Problems with single frequency apex-locators occurred due to the presence of electrolytes in the canal. Thus, new generation of locators has been introduced – impedance is now measured on two frequencies and the position of apical constriction is calculated from corresponding impedance ratio. The aim of this paper is to examine properties of the impedance-ratio method and to compare it with single frequency measurements. Experiment was carried out in-vitro. Exact position of apical foramen on each tooth was measured with microscope. Then the teeth were placed in a freshly mixed alginate, commonly used in such measurements. Impedances were measured on frequencies commonly used by apex-locators, and with Kerr file positioned at apical foramen at several positions above and under it (in steps of 0.25 mm). Measurements were performed in dry canal and in canal filled with electrolytes usually used in endodontic treatment. Sensitivity on different type of electrolytes and sensitivity on electrode displacement were calculated for single frequency and frequency-ratio technique in order to investigate the benefits of each. By comparing them with calculated variation coefficient of raw measurements we concluded that the frequency-ratio method (used in new generation of apex-locators) is more robust to electrolytes, but its sensitivity decreases in normal condition of the dry canal. For achieving full credibility of imposed conclusion, in-vivo verification should also be performed.

Evaluation of Electrical Equivalent Circuits of a Tooth: Comparison of Circuits with Resistors and Capacitors and the Circuit with a Constant Phase Element

During the endodontic treatment electronic devices called apex-locators are used to determine the root canal length of the tooth. Apex-locators measure the electrical impedance of the root canal and display the position of the electrode inside the canal. In order to better understand physical phenomena inside the root canal and to improve the measurement procedure, tooth is modeled by an electrical equivalent circuit. In this paper eleven different electrical equivalent circuits comprising of frequency independent resistors and capacitors are examined and compared to a simple equivalent circuit which contains a constant phase element. Impedance measurements were performed in vitro on extracted tooth immersed in alginate dental impression material. Quality factors are calculated to compare the fit quality and parameter utilization efficiency for each considered electrical equivalent circuit. We have found that five-element circuit shows superior performance in both fit quality and parameter efficiency among circuits comprising of resistors and capacitors. However, it can not compete with a simple equivalent circuit that contains a constant phase element.

Adaptable Measuring Instrument for Wireless Dynamic Strain Monitoring on Moving Objects

Dynamic strain monitoring provides valuable information about behavior and condition of mechanical parts subjected to the load either under test or realistic working conditions. In many occasions, test points for strain measurement are not easily accessible for temporary or permanent wired connection with standard test and measurement equipment, especially for measurements on moving objects. We developed a configurable portable dynamic strain monitoring system, which is particularly suitable for short-term installations and adaptable for wide range of expected strain values. The high-accuracy measuring module, attached to the test point along with the strain gage sensor, digitizes and transmits measured data over the license-free ISM radio-frequency band to the receiving unit for further signal processing and results representation. The calibration procedure is highly simplified due to the specific design of the input analog measuring chain, which eliminates the need, in several commercially available similar instruments, for manual sensor calibration. The accuracy and the bandwidth of the input measuring chain were optimized to provide means for high quality spectral analysis of acquired dynamic strain waveforms. The system may be simply extended for dynamic torque, power and rotational speed measurements on revolving shafts, by connecting to the inductive proximity switch to the receiver module. Receiving unit also provides means for connection with other test and measurement equipment by standard analog and digital industrial communication protocols (4–20 mA current loop, RS485). The overall system was designed to accommodate to wide variety of test and research applications, as well as monitoring parameter ranges.Copyright