Customer | Suiker Unie
Project | Safe, efficient signal transmission between field devices and control system
Location | Groningen, Netherlands
Completion | Status October 2012
Between September and January, intense activity takes place at Dutch sugar producer Suiker Unie. During these “sugar campaigns”, a truck filled with sugar beets reaches the plant at Groningen and is unloaded every two minutes on average. At this factory alone, Suiker Unie produces 450,000 tons of sugar each year. Three million tons of beets have to pass through different stages of the production process to generate the sugar: wash, shred, boil, crystallize – the path to tons of sugar requires a safe and efficient process control.
In that regard, the reliable acquisition and interpretation of measured data between sensors in the field and the control level is a fundamental requirement. One of the most well-known faults here are ground loops. These occur in the field and on the control side when several ground connections with different potentials exist. This generates a compensation current in the signal lead and influences communication in such a drastic way that reliable process monitoring and control are no longer possible. Furthermore, Suiker Unie asked for reliable monitoring of the various drive motors of conveyors, drum dryers, and centrifuges at the plant.
The solution for the ground loop problem is a galvanic isolation of field and control sides. It denies the overlay of the signal caused by interference voltages and interference currents. With regard to the branched plant structure of Suiker Unie, a galvanic isolation offers the best solution to prevent ground loops during the transmission of analog and digital signals. The same goes for long cables which can catch common mode noise by electromagnetic coupling and send into signal inputs.
Pepperl+Fuchs' portfolio offered what Suiker Unie was looking for. Signal conditioners in which either a transformer or an optocoupler is included establish a galvanic isolation. This interface module interrupts electrically conductive connections between field and control side so that the charge carriers cannot flow from one to another. Instead, the transmission of the process signals is carried out by the magnetic field or an optical sender/receiver system.
Among the most important functionalities of a signal conditioner is the conversion of field signals into standard signals. This is necessary to make different field variables usable for control systems. Signal conditioners from Pepperl+Fuchs detect the signals of thermocouples, resistance temperature detectors, or other devices and convert them into 0/2…10 V or 0/4…20 mA standard signals. The conversion to 0/4…20 mA is also possible for binary frequency signals by NAMUR sensors or mechanical contacts. Users program these functions quickly via DIP switches on the front side of the devices or with their PC.
The monitoring of motor engines that Suiker Unie asked for is also ensured by the signal conditioners: they compare the actual rotational speed to a pre-selectable trip value. The rotation speed value is provided as a binary signal by a NAMUR sensor or a mechanical contact. Inside the rotation speed monitor, the actual rotational speed is compared to a trip value, which can vary from 1 mHz to 12 kHz. Whenever the rotational speed is outside of the defined range, an alarm is triggered.
Throughout the busy sugar campaigns, signal conditioners by Pepperl+Fuchs contribute to a reliable and quick production process at Suiker Unie. In this way, plentiful beets are converted into high quality sugar for the international market.