With the 21 D RFID and 21 DC RFID series, Keller is launching passive print transponders. The transponders in the 21 D RFID series can be used indefinitely without maintenance thanks to their energy independence. A special feature of the 21 DC RFID series is the integrated data logger with a long-life special battery. Both devices are powered wirelessly via the RFID interface to transmit the measured values. The pressure transponders are based on the supplier's '7 LD' series pressure transmitters; Microsensys is responsible for the transponder technology. The usual plug for electrical connections has been replaced by an encapsulated RFID transponder made of impact-resistant plastic; all parts in contact with the media are made of stainless steel. This means that the print transponders in the series are immune to environmental influences and vandalism. The measured values can be read out using an RFID reader and transferred directly to a laptop via USB. Alternatively, a battery-operated pocket reader can be used, which displays the measurement data, stores it in memory and makes it available as an XML file for transfer via USB. With the pressure transponders of the '21 DC' series (DataCollector), the data logger registers the pairs of values for pressure and temperature at intervals of between 10 seconds and 255 minutes. Depending on the configuration, the measurement mode stops when the memory is full (2048 measurements), overwrites existing data (ring mode) or initiates a sleep mode.