As pump systems become more automated, decentralized control of equipment components is becoming ever more widespread. With the simultaneous reduction of both maintenance and operating resources, automatic monitoring is increasingly used in the efficient deployment of plant. High costs do not allow the luxury of equipment that is rarely utilized during a systems’ operation. Therefore, it is important that the operator is fully informed on the current operating state of the system.Because of their leak-tightness, diaphragm dosing pumps are used in almost all segments of the industry where the exact addition of low to medium viscosity, and sometimes expensive fluids, is required. It does not matter whether these are neutral or critical media as PTFE diaphragms and a variety of chemically highly resistant pump head materials permit the delivery of nearly all common chemicals.Furthermore, because its characteristic curve is insignificantly impacted by the counterpressure, the diaphragm dosing pump is particularly suitable for accurate dosing processes. This key feature means that communication options with the rest of the pump system must be created. Although in many cases, the pump only represents a small portion of the overall cost of the equipment, it is frequently the core of the whole system.
Integrated electronics
Dosing pumps for small delivery rates with integrated control electronics have been available on the market for quite some time. However, few providers offer corresponding pumps for flow rates up to 1000 l/h. The number of potential suppliers drops even more for capacities up to 1.5 m3 per hour.The reason lies in the pump control, which becomes more elaborate, and thus costly. With increasing motor output, many manufacturers are not able to realize an economic price level compared with the central control and monitoring of the pump and its periphery.The question arises, which selection or signal exchange capabilities a dosing pump must possess, or how can it be ensured that possible interferences do not negatively affect the dosing accuracy?When picturing the general design of a dosing system, a chemical container is usually positioned at the suction side of the dosing pump from which the liquid is extracted. On the pressure side, the chemical is transported to the process via a dosing point. To make sure the pump adds the correct volume in relationship to the process, it shall receive an external signal which controls the stroke frequency of the machine.The production process is further influenced, among others, by the fluid level in the chemical container, the counter pressure in the system and the flow characteristics of the liquid and the condition of the diaphragm. The diaphragm undergoes the most wear and should be monitored permanently.At first sight, the requirement profile seems to be rather simple. However, when taking a closer look one will quickly realize that the pump must be designed in a multifunctional manner if it is to be able to process all common input signals and even offering the capability of optimal adaptation to the dosing process. This means, that an abundance of control and monitoring options makes a quick and unsophisticated operation of the pump almost impossible, depending on the conditions.The model series C 410.2 (Figure 1) series of leak-tight pumps diaphragm dosing pumps from sera (Seybert & Rahier) covers a capacity range up to 1.45 m3/h at maximum counter pressures up to 8 bar.A number of suppliers have therefore opted to equip the pumps only with the control and monitoring options required for the particular application. Although the operation as such is simplified by this measure, the system operator is later forced to incorporate a new pump if, for example, the selection of the pumps changes due to the optimization or expansion of the system.
New generation
The diaphragm dosing pumps of the new C410.2 generation principally possess all available selection options that can be activated with the help of straight forward menu navigation. Apart from the robust and reliable mechanical design, the new development ensures that the pumps are equipped with a multifunctionalbut easy to be operated control electronics.A factory-set basic configuration allows the operator to integrate the pump immediately into his system via ‘plug & dose’ and then start its operation. If this configuration is not sufficient, he can adapt the configuration to his requirements using the control buttons on the outside of the control electronics and following the menu navigation on the display. Apart from the simple operation, the chief advantage lies in the fact that the operator can always adapt the pump to his process. This means that pumps integrated into systems with their level of automation being increased over time, do not need to be replaced, as is the case with many manufacturers providing only basic features, but only reconfigured.Based on this background, the new C pumps can be equipped or upgraded with various accessory modules. For example, flow measurement is realised with the help of a device installed to the outside of the pump. The delivery rate of the pump, determined by the flow meter, is indicated on the display in l/h. An automatic adjustment is made if the target and actual values do not match.The diaphragm dosing pumps of model series C 410.2 exhibit a special feature in regard to stroke frequency. They can be operated both in single stroke and in frequency converter mode. While the single stroke control is often preferred for batch dosing (e.g. filling of small volumes in a short time), the frequency converter mode is beneficial especially when delivering media with relatively high viscosity. The stroke velocity can be optimally adapted to the rheological properties of the liquid via Slow Mode.The communication capabilities of the C pumps is documented, among others, in that they can be optionally selected via external pulse and analogue signals. Direct PLC inputs, two status outputs and the capability of being able to record and further process different fluid levels ensure that the pump provides additional process transparency, making external switching devices that would create additional costs, obsolete.Apart from the display of the current flow, the dosed quantities are added up. This provides access to additional important process-relevant data via the pump.
PROFIBUS
Comprehensive and interrelated communication between the field units and a central control station is indispensable in the modern process industry. Field devices may be sensors, actors or also electrical machines such as dosing pumps. Field bus systems are networks that allow machines and devices to digitally communicate with each other within a production chain (Figure 2).All sera pumps of the C model series (Figure 3) can be equipped with the worldwide most successful field bus system: the PROFIBUS. Because of its modular structure, this field system is the only one that can be employed in all areas of automation engineering without limitations. Almost all automation components are nowadays available with a PROFIBUS interface. They communicate via the communication protocol PROFIBUS DP.The employment of the PROFIBUS field bus system and corresponding devices provides the plant operator with many advantages:• A continuous bus system for the entire plant• Interchangeability of the devices through an internationally standardized interface• Worldwide acceptance and proven in the field• High flexibility for the expansion and upgrade of existing installations• Comprehensive diagnostic functions for high plant availabilityThe PROFIBUS DP interface replaces the conventional selection options per analogue or contact signal and permits trouble-free integration of the dosing pumps in complex plants of the process industry. The dosing pumps are integrated into the PROFIBUS system of the plants with the help of the so-called GSD file. This file contains all important device master data and permits easy integration via ‘plug & play’. The user can choose between manual and PROFIBUS selection of the pump. The current flow of the dosing pump is not only indicated on the display but, with the flow meter connected, is also reported digitally via the bus. The warning and fault messages of the dosing pump are issued individually which allows possible errors to be diagnosed and remedied even more efficiently. An unscheduled plant shutdown can thereby be prevented to even a greater extent.Finally, it shall be pointed out that the new C model series was designed with the focus on industrial applications, ease of operation and high communication capabilities. This concept ensures cost savings during the construction and future operation of the plants. Contact:Seybert & RahierGmbH + Co. Betriebs-KGsera - Str. 134376 ImmenhausenPhone +49 (5673) 9990Fax +49 (5673) 999 155info@sera-web.dewww.sera-web.de
