Refineries, chemical and pharmaceutical plants, or food and beverage production sites rely on accurate flow measurements. In breweries, for example, there are tens of different liquids that need to be constantly monitored in order to obtain products of the highest quality: Water, fermentation residues, wort, cooling and heating liquids, cleaning agents, waste water and, of course, the beer itself. The temperature of the individual liquids varies greatly in the course of the brewing process, and both the flow velocity and the flow rate are anything but constant in such plants. Nevertheless, all media must be precisely localizable and controllable at all times. Siemens demonstrates how this can be done safely and conveniently with a flow measurement system centered on the Sitrans FST070 technology module. It combines the advantages of clamp-on technology with those of decentralized automation solutions and simple integration into higher-level control and instrumentation systems without any significant programming.

Modular IO system

Sitrans FST070 is not a classic transmitter in its own housing, but a pluggable module for the Simatic ET 200SP peripheral device. This means that the transmitter only requires a place in the Simatic peripheral device, where it can be combined with other modules as required. This combinable flexibility has characterized the IO systems of the Simatic ET 200 product family for decades. Thanks to the individual configuration options of a large number of different plug-in modules, the peripheral device can be adapted to all applications. This is due on the one hand to the simple scalability - the system can be expanded step by step - and on the other hand to the wide range of functions offered by the modules. It ranges from soft and motor starters to weighing and dosing tasks to hardware-based signal processing for fast counting, measuring and position detection of different encoders. Now, the Sitrans FST070 can also be used for precise detection of volume or mass flow.

Clamp-on sensors for more flexibility

The module works together with Sitrans FSS200 clamp-on ultrasonic sensors. The ultrasonic measuring principle can be used to monitor almost any flow process, for example in breweries. The sensor pairs are attached to the pipelines from the outside. The measurement technology neither comes into contact with nor influences the medium. The ultrasonic sensors provide precise results for a wide range of liquids or gases with different flow velocities.

Since the transducers are non-invasive, commissioning, operation and maintenance are low cost: pipes do not need to be cut open, there is no pressure loss, and ongoing operations do not need to be interrupted for installation. The measuring technology has no moving parts, is easily accessible and practically maintenance-free, as it does not come into contact with the media to be measured. The clamp-on mounting technique is suitable for all common pipe materials and can be used for pipe diameters between 10 mm and 10 m. Sitrans FSS200 ultrasonic sensors can be used up to pipe wall thicknesses of 1 to 35 mm, and up to 65 mm on request.

Digital communication and four-channel measurement

The Sitrans FST070 and the measuring system are connected to the external Digital Sensor Link (DSL). This digital module converts the analog signals from the ultrasonic sensors into digitized flow data. These are then sent to the Sitrans FST070 technology module for further processing. Up to four independent measurement paths can be attached to one pipe section. Multiple penetration of the pipe from different angles ensures even greater measurement accuracy and reliability. The DSL is installed close to the sensors. The sensor cables, which are thus short, offer optimum suppression of high-frequency interference. A Siemens Sensor Link (SSL) cable transmits the digitized flow data in real time over a distance of up to 150 m to the technology module. This keeps cabling requirements to a minimum while achieving consistently high measurement accuracy without interference.

Integration by drag & drop

The ultrasonic flow transmitter can be integrated directly into the Simatic PCS 7 process control system or into current Simatic controllers via the TIA portal. Profinet-capable standard controllers are also supported. Safe integration into the automation system is achieved using the faceplates supplied and Step 7 or the Simatic PCS 7 engineering system. The two digital inputs and outputs of the transmitter are connected and parameterized by drag & drop with the aid of the function blocks. Programming knowledge is not required for this. The faceplates are system-tested and support future updates or upgrades.

Real-time data processing – even in hazardous areas

Sitrans FST070 processes the data from the DSL, resolved at 100 Hz, in real time and establishes fast and interference-free digital communication with the higher-level PLC. An update rate of up to 10 milliseconds is achieved. In this way, even time-critical measurement tasks are processed reliably. In this way, the plant operator can always control rapid changes in flow rates, such as those that occur in breweries during CIP processes when changing product and rinsing water. The transmitter is not specifically designed for the beverage industry, but can also be used in applications with potentially explosive atmospheres: the module has Atex Zone 2 Class 1 approval, and with the Sitrans I300 barrier module it can be used up to Zone 1 Class 0.

The Sitrans FST070 technology module makes flow measurements in plants retrofittable. By embedding in the decentralized IO technology of the Simatic ET-200SP peripherals on the one hand and the connection to the clamp-on technology on the other, the system offers maximum flexibility. Integration into higher-level controllers or control systems from the Simatic portfolio is possible through the drivers and faceplates. The interaction results in exact measurements of volume and mass flow - with maximum user-friendliness and minimum installation effort.

Author
Jürgen Kiefer, Product Manager Flow