Phone: +385-1-6 129-977, Fax: +385-1-6 129-652, Absfracl -A prototype of a porrnhlc wireless measuring sysremfoor monitoring moror shafr torque. power and romtivnul speed was developed and restid The sysrem was designed ro offer a great /Ze.ribilir?; for wide variety of resf and research applicarions (IS well us rhe rrionitorin!: paranterer ranges. Strain gauge sensors, placed onto the revolving shufr d o n g with U \vir-eless mdiolfrequency rransmitrer, are employed 10 measure t <~r p e .Shaft mruriotml speed i.y measured by using the rotarj encoder. Torque ond power are calculared automatically on the receiver side from samples processed in U rcnl rime and displayed t o rhe ~s e r . Moreover, system provides analog and digiral outpurs oJ'the shaft vibrarion waveform for oscilloscope observing or recording IO a personal computer in a digital format. Keywords ~ Rei~olving Shufr Measurements, Srrain Gauge Measurements, Torque Meusurements, Wireless sensor.^ I. WTRODUCTIONThe most important mechanical parameters monitored on revolving motor shafts for test and meusurement purposes are torque, power and rotational speed. They contain important information about the functional performance and the motor behavior under simulated and realistic conditions. Moreover, they inay be useful to indicate possible motor problems and malCunctions in an early stage.The interconnection among these parameters is given by the formula (1):where P is the motor shaft power (kW), M the torque (kNm) and n the rotational speed (5~'). Equation (1) yields the Fact that it is sufficient to measure rotational speed and torque in order to derive motor shaft power. The appropriate sensors and transducers need to he employed to convert these quantities into electrical signals.The rotational speed is the most usually measured directly by using rotary encoders. The choice oC methods for torque measurements include strain gauge sensors, magnetostrictive trmsducers, twist angle ineasurements etc. The approach by using strain gauge sensors was chosen due to its inherent simplicity. precision, flexibility and reliability. Thc strain gauge sensors are arranged in a Wheatstone bridge circuit and mounted to the shaft, so that the one gauge measures increase o C the length in o tension direction, while the other one measures decrease [I]. Voltage mcuured by a differential amplifier on a bridge diagonal is converted to a torque value hy means of the formula (2):where Rt is a strain gauge bridge nominal resistance (R), Rx a shunt calibration resistance (kR), K, a strain gauge bridge constant. G a shear modulus (N/m2), D the outer shaft diameter (mm), Du the inner shaft diameter (mm), U, a voltage output from shunt calibration, Um0 a bridge zero calibration voltage and U the measured voltage from strain (all voltage values expressed either in (V) or AID converter digits).The approach of measuring torque on a revolving shaft by using the strain gauge sensors implies that the analog processing circuitry must be attached directly to the shaft. Moreover, the meas...

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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.