5 months ago

MDA Technologies 3/2014

MDA Technologies 3/2014

MEasurement and control

MEasurement and control Pressure measurement made to order Walter Felber Pressure is measured in many technical systems in different conditions and requirements. As the number of necessary variants of electric pressure transmitters rises, the batch sizes in production must decrease. To still meet demand in an economical way, Sensor-Technik Wiedemann GmbH (STW) aims for a “modular system for pressure transmitters”. Author: Walter Felber, Project Manager at Sensor-Technik Wiedemann GmbH, Kaufbeuren Germany Huge variety in pressure measurement Pressure transmitters measure pressure. That is about the only thing different pressure transmitters have in common. There is a range of possible differences when it comes to pressure measurement. The differences in their application and as such between the pressure transmitters are shown in Figure 01. A normalization or reduction of the resulting variety of options is often technically impossible and is thus unlikely in the near future. Due to new requirements such as USB or Power Over Ethernet, the number of options is more likely to increase than decrease. The cost-effective production of rarely required versions remains a challenge. Customers, however, want suitable pressure transmitters on time and at the lowest possible cost. Solutions All pressure transmitter manufacturers are facing this challenge and are addressing it with a range of solutions. To pass on the high cost of products that are made to order to the customers is not innovative. Another concept works by defining several series types which help narrow it down: “Hydraulics”, “low-pressure range”, “atmospheric gases” and other specifications that limit the options named above. However, the transmitter series of different strengths stocked by STW so far weren’t always sufficient to meet the demand for a wide range of different types. It was often just a matter of time until a needed combination couldn’t be achieved with any of the transmitter series. Another disadvantage for the customer was that he had to choose one or more of 50 MDA Technologies 3/2014

the series and adapt to them, which often meant a compromise. Moreover, the search, selection, qualification, supplier diversity and documentation of different series created a lot of work and effort for the customer. It was necessary to supply a transmitter series that meets as many requirements as possible. A modular system for pressure transmitters is produced STW has decided to create the “universal transmitter with customizable properties”: the M01 modular system. This transmitter series is designed to cost-effectively achieve as many combinations as possible through modularization and standardization of module interfaces. The customer checks the suitability of the M01 once, defines further variants and, apart from that, can rely on the same properties. The customer can choose from an unusually large number of different modules to adjust the transmitter series to existing installation situations. The transmitters used are always the “same” and only differ in ways that the customers wants them to. Not all of the modules required to create all possible variants are yet available, but the existing selection is already remarkable (see Figure 02). In purely mathematical terms, the customer can choose from around 1.5 million different pressure transmitters that can be built with these modules. Figure 03 shows a selection of modules. Modularity exemplified by electronic components 01 Differences in the pressure measuring tasks and subsequently the pressure transmitters ter, threads with integrated temperaturedependent resistors are mounted instead of pressure connectors. Other physical variables can be added to the modular system based on a bridge circuit or a single resistance. Table 1 provides a detailed list of the modules already available for pressure transmitters. Since the same modules can be used in all versions, they can be manufactured economically in large quantities. Customer-specific modules also possible The modular system makes it possible to integrate customer-specific modules, enabling the connector plug, which has been adjusted based on the specified interface to the remaining transmitter, to be adapted with a minimum of effort and expense in terms of development and qualification. The adjustment of data protocols is also a routine matter with digital versions. Details, such as different plug colors 02 The modular system for pressure transmitters 03 Several modules for pressure transmitters To achieve the modularity for the electronic requirements, necessary functions are divided into three circuit boards so that customers’ requirements can be taken into account by selecting the appropriate circuit board. The interfaces between the modules have to be very clearly defined in order to ensure that every possible combination meets the functional requirements: n Input board: Processes the signal of the measuring sensor and normalizes it. n Amplifier board: Resets to the normalized signal of the input board to the desired output signal or the digital output bus. n Output board: Filters EMC interference and adapts the electronics to the different dimensions of the connector pins. The three boards are easy to put together − like toy building blocks. By selecting the appropriate amplifier board, an analogue 0 ... 10V transmitter or a transmitter with CAN output can be created. Figure 04 shows how the boards are put together. In order to create a temperature transmitdepending on the pressure range, have likewise been integrated into the modular system according to customer request. However, accounting for such details often presupposes a quantity-to-cost ratio like that of the “typical” production of trans- MDA Technologies 3/2014 51


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