NOVOTECHNIK MESSWERTAUFNEHMER OHG

From here onwards, we are only concerned with the linear characteristics (linearity). Relationships must be suitably adapted for applications with non-linear characteristics (conformity) but there are no essential differences. As already mentioned in Section 2, the required linearity values can only be utilized so long as the signal output by the sensor "potentiometer" carries no current. We have now to consider the effect of wiper current on linearity. Fig. 10a illustrates the functional relationship between wiper current, contact resistance and linearity error. As is shown by the example in Fig. 10b (Characteristic 4), with a wiper current of 10 µA and a contact resistance of 10 kOhm, a potentiometer which has a resistance of 2 kOhm already has linearity error of 1.1 %. A similar situation arises with an ohmic load. This clearly shows how important are the roles played by both wiper current and contact resistance. Fig. 10a Fig. 10b

If there is axial misalignment (eccentricity) between the drive shaft and the shaft of a potentiometer used to sense angular, motion, this will cause a linearity error that increases as the coupling radius decreases in relation to the degree of eccentricity. The following equation determines the maximum relative error Fmax = E/Pi · rk where E = Eccentricity und rk = the coupling radius. It is only possible to take full advantage of the linearity or conformity of any rotationary sensor system, if coupling alignment errors (offset and angular misalignment) are avoided or at least reduced to a mimimum. This means that with highly accurate measurement systems, due allowance must be made for any coupling misalingment in accordance with the above equation.

When, some 60 years ago conductive plastic potentiometers were first introduced onto the market, it was apparent that although the winding jumps which were a feature of wire-wound potentiometers had been overcome, absolute smoothness of the output voltage could not be achieved. Following some basic reserach by. h. Wormser 4, 5, 6 , the term "smoothness" was included in the standard issued by the Variable Resistive Compontents Institute (VRCI). Although this definition was adequate at that time it cannot serve as a system definition for many applications. This is because it is now possible to produce potentiometers with appreciably better smoothness and linearity values. For this reason, Novotechnik has sought over the past years to develop definitions better suited to the current state fo the art. The various methods used are discussed and evalutated below.

Smoothness is a measure of the deviations from perfect regularity that appear in the output voltage of a potentiometer. This irregularity is measured over a specified travel increment, for example 1 %, and is expressed as a percentage of the applied voltage. For the measurement of smoothness, the VRCI definition calls for a bandpass filter to be used as a means of suppressing any linearity error and for the potentiometer to be operated with a load resistance (e.g. 100 . Rp). This method has certain disadvantages: a) The use of a filter causes both the absolute wiper velocity and any changes in such velocity to affect the smoothness values. Since the filter partly integrates and partly differntiates, the chart-recorded smoothness curve does not accurately indicate the variations in the output signal. b) The load applied to the potentiometer also contributes to error by causing variation in the contact resistance which is greatest with the wiper at the voltage application end and...

In 1978, Novotechnik introduced the term Microlinearity, which is defined as the maximum linearity variation within a travel or angular increment that amounts - as with smoothness measurement - to 1 % of the electrical range if nothing to the contrary is defined. Microlinearity is indicated as a percentage of the absolute voltage that is applied. Fig. 11 illustrates the characteristic obtained for a potentiometer with a microlinearity error. This was evaluated by a computer-supported system while making linearity measurements. The travel increments are super-imposed on the linearity curve and have an overlap of at least 50 %. Contrary to a smoothness measurement, the error here is pureley a linearity error that describes the maximum error within a defined increment. Microlinearity does not, however, make it possible to determine whether a potentiometer will be suitable for a particular applications because any variations in gradient (sensitivity) can only be determined with...

If, in a highly sensitive control system, the amplification should, for example, be so arranged that the control circuit will be stable with the mean slope (gradient) of the sensor, then it is important to be aware of any variations there may be in that slope (Fig. 12a, Fig. 12b). If, at any point, the gradient is appreciably steeper than the mean gradient, then there will be a higher closed-loop gain in this position and this could lead to feedback oscillation. If, on the other hand, the gradient is less steep at some point than the mean gradient, then repeatability would be reduced and there would be less control accuracy. If we relate this type of local gradient variation gl to the mean gradient go of the potentiometer, then this criterion is independent of the potentiometer length and can be used for the direct comparision of various potentiometers.

The synchronous serial interface is a digital interface for absolute position and rotary measuring systems. It enables position and angular information to be transmitted digitally, absolutely and without bus overhead. As a result, it is especially well-suited for applications in which reliability and signal robustness are required in an industrial environment. Transmission is synchronous to the request of the controller, and one bit of the position value to be output is transferred with each clock pulse. The clock/data signals are transferred differentially via an RS 422 interface. Data formats are binary or Gray-encoded with a 24 or 25-bit position resolution. A parity bit for increased data security can also be attached to the data format ("SSI26"). Possible clocking frequencies are in the range from 60 kHz to 2 MHz, and update rates of up to 16 kHz can be achieved. The maximum achievable clocking frequency is dependent on the cable length and the driver blocks used. This...

In December 2009 the new Machine Directive 2006/42/EC of the European Parliaments went into effect, and with it a number of new legal ordinances with which, among other things, the so-called "Functional Safety" of devices and systems is to be ensured. The goal is to limit the risk of endangerment of human beings, the environment, and investment goods. This is to be demonstrably achieved with systematic error avoidance, error detection, and in particular error control. All devices and systems, which can result in the death or injury of human beings, in catastrophic damage to the environment or in destruction, for example of production systems, in the case of an error must be classified as "safety-relevant". The applicable safety standards must then be applied during their design, development, manufacture and operation. Today we find safety-relevant systems in many industries supplied by Novotechnik's sophisticated, innovative products. In the industrial sector this is the case,...

Die Idee und das Ziel von Industrie 4.0 ist es, in Echtzeit alle relevanten Daten innerhalb von Wertschöpfungsprozessen zu gewinnen, um daraus Optimierungen hinsichtlich Kosten, Ressourcenbedarf und Verfügbarkeit abzuleiten. Dies ist möglich, wenn alle an diesem Prozess beteiligten Komponenten vernetzt sind und die notwendige Information für Bewertung und Aktion bereitstellen. Ein wichtiger Faktor sind dabei Sensoren, die Zustände innerhalb von Fertigungsprozessen und Anlagen erfassen und diese an übergeordnete Systeme wie Steuerungen kommunizieren. Die Standardisierung dieser Kommunikation ist außerordentlich sinnvoll. Novotechnik bietet dazu Weg- und Winkelsensoren mit dem herstellerunabhängigen Kommunikationsstandard IO-Link an, welcher die Eigenschaften intelligenter Sensoren voll nutzbar macht. IO-Link kann über Gateways in unterschiedlichste Bussysteme implementiert werden und ermöglicht über intelligente Diagnose- und Parametrierungskonzepte eine deutliche...