PTT 280, 380 AND 480 WHITE PAPER

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1 PTT 280, 380 AND 480 WHITE PAPER MC-m develops and markets integrated and comprehensive predictive health monitoring solutions for rotating machines in power generation and mining. For more than 15 years, our technology has been successfully implemented in major power plants worldwide and in open-cast mining.

2 Innovative sensors family Abstract This paper introduces an innovative family of displacement probe developed by MC-monitoring. These sensors are based on inductive electromagnetic measurement principle. These probes are typically built into machinery to detect the motion of shafts inside journal bearings or the relative motion of other machine elements. Highly Integrated Intelligent Contactless Proximity System, whit built-in linearization, active temperature compensation and Modbus RTU interface for industrial and laboratory applications. At present, there are numerous commercially available proximity sensors systems which are generally composed of three elements a) The probe with his integral cable b) The extension cable and c) the driver or oscillator. The new approach proposed by MCm consists in an enhanced and integrated probe housing including not only the sensing element but as well all the electronic circuitry required to build the measurement system in the head of the probe. The main objective of the system integration is to provide tangible benefits by improved power/energy density of components through the reduction of mass and volume as well as to cost reduction through higher functional integration and easy deployment of novel measurement system to serve multiples industrial demanding application whit no compromise for the performance. Contents Abstract 2 Eddy current operating principle 3 High-performance vs inexpensive sensors 3 Target Material 4 Calibration on the field 4 Active temperature compensation 5 MCm Smart and Intelligent Sensor Family 5 Smart Smart sensor is a combination of a sensing element, an analog interface circuit, an analog to digital converter (ADC) and a bus.. Intelligent Intelligent sensor is the sensor that has one or several intelligent functions such as self-testing, self-identification, self-validation, self adaptation, etc. Page n 2

3 Operating Principle MCm Proximity Probe Family PPT-280 PPT-380 PPT-480 Voltage outputs Voltage or Modbus RTU (software configurable) 4-20mA output interface All the MCm PPT family can be configured and calibrated on the field with the MCm Sensor Manager software. Eddy current operating principle The displacement electromagnetic probes measure the relative distance (proximity) as a function of electromagnetic coupling between the face of the probe and the target. The probe relies on inductive effects requiring an electrically conductive target. The probes use eddy currents generated in the target as its sensing and measurement mechanism. Figure 1 When an electrically conductive material is placed in the coil s dynamic magnetic field electromagnetic, induction will occur and eddy currents will be induced in the material. More precisely, these sensors use the energy dissipated by the eddy currents. The greater the distance from probe to target, the less electromagnetic coupling, the lower the magnitude of the eddy currents, and the less energy they drain from the probe. High-performance vs inexpensive sensors Make a distinction between high-performance eddycurrent sensors and inexpensive inductive sensors is important to get expected measurement results an entire satisfaction. Simple inductive sensors, such as those used in inexpensive proximity switches, are comparatively unsophisticated devices allowing them to carry a low price but as well poor performance. The high-end category of eddy-current sensors for use in accurate displacement measurement, metrology or vibration applications uses complex electronic designs to accomplish complex mathematical algorithms. Unlike inexpensive sensors, these high-performance sensors have outputs which are extremely linear, insensitive to the temperature changes, and able to sense very small changes in target position resulting in high resolution measurements. Proximity type sensors are very useful in automation applications and many commercially available models and are well made for their intended applications, but they are not suited to precision metrology applications in harsh environments. Figure 2 PPT-x80 Overview Page n 3

4 Abstract Field Experience Target Material Inductive eddy current displacement sensors require an electrically conductive target. The coil is excited by a high frequency AC signal. The less resistive the target, the more eddy currents are produced in the target. This improves sensitivity and signal to noise ratio, ultimately increasing resolution. Figure 3 Figure 3 FCB-280 (Field Calcibration Bench) is a tool allowing to fix the sensor against the shaft for calibrating the PPT-X80 on site There are large quantities of materials electrical conductive materials that have been successful targets for eddy current sensors. To give an idea a non exhaustive list of target materials and their resistivity values are shown in the graph below. Calibration on the field Traditionally, eddy current sensor systems require to be calibrated for a specific target and specific material characteristics in the gap between probe and target. This is due to the fact that the impedance change of the probe is dependent on the electrical properties of the target material. Generally, the probe systems state the material to which they are calibrated (typically AISI 4140 steel). However, if the target material has different characteristic, the performance deviation could be excessive for the intended application. Figure 4 Figure 4 PPT-990 allows to connect the PPT-x80 to the MCm Sensor Manager via a proprietary protocol over RS-485 Since the PPT280, PPT380 and PPT-480 sensors are user configurable through the MCm Sensor Manager software, the calibration can be done on site with help of the Field Calibration Bench (FCB-280) and the PPT-990 which can be ordered as accessories with the sensors. Resistivity Silver Copper Gold Zinc (cast) Bronze 1030 Steel Carbon Steel ANSI Steel Iron (cast) 4130 Steel Titanium Figure 4 Typical material resistivity 22 Figure 6 Raw output of PPT-X80 depending the material resistivity The benefice of a field calibration is to be sure that the calibration of the eddy current probe is done on the good material and to avoid measurement deviation. Furthermore, in many case, it could be very difficult to find a sample of the material used for the machine shaft and the only way to achieve the calibration is to do on site. Page n 4

5 Abstract Build in Technology Active temperature compensation MCm smart and intelligent proximity probes have a build in temperature sensor used to monitor the ambient temperature. This temperature value is then used to compensate in live the deviation of the output signal due to the temperature change. MCm Smart and Intelligent Sensor Family PPT-280 Smart Sensor with voltage output The PPT-280 is innovative eddy current proximity probe with a linear voltage output depending on the distance to the target. Etc PPT-380 Smart and Intelligent Sensor with built in Modbus RTU A Modbus RTU interface has been implemented in the PPT-380 sensor allowing the user to interconnect of up to 32 sensors on the same serial bus line and gather characteristics values (Mean, Peak to Peak, Min. and Max.)from each individual sensor. Furthermore, the PPT-380, when used in Modbus RTU mode, can use its analogue output as a digital output +0VDC / +24VDC to trigs an Alert or Danger. Alert and Danger can be configured using the MCm Sensor Manager. PPT-480 Smart and Intelligent Sensor with 4-20mA output interface A 4-20mA interface has been implemented in the PPT-480 sensor and can be configured for vibration displacement monitoring (Peak and Peak to Peak) or axial thrust position (GAP). PPT Family application Single or Redundant Thrust Position Generator/Turbine Shaft Vibration Eccentricity Phase and Speed Monitoring thrust position detects any significant overload or wear in the thrust bearing. Generator and turbine shaft vibration monitoring complements bearing vibration monitoring by detecting radial loads, unbalance (mechanical, hydraulic, etc.), and bearing fatigue. Eccentricity probes detect any significant rotor bow or a change in position caused by bearing wear. Monitoring shaft rotation from a notch (key) provides a rotating speed and vibration phase measurement to enable analysis of phase differences between multiple bearings along the same shaft. Page n 5

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