A fieldbus is an industrial communications system which e.g. connects a plurality of field devices such as measuring probes (sensors), control members and drives (actuators) to a control device. In this connection, as a rule, a fieldbus system replaces a complex and/or expensive parallel wiring of the fieldbus components with a substantially more cost effective serial networking for digital data transmission.
In the simplest case, sensors are connected directly to the fieldbus. An improvement with respect to the direct connection is described, for example, in DE 103 53 345 A1, according to which so-called fieldbus gateways serve for the coupling of a sensor to the fieldbus. They effect a conversion of data in the data format of the fieldbus into a data format which is understood by the sensor, and vice versa, in order thus to permit a problem-free communication between the sensor and the fieldbus. Not only the hardware-side connection of sensors which are very small in part to the fieldbus is thus possible, but also a connection of a specific sensor type to different bus systems. The connection function is transposed from the sensor into the gateway.
External gateways of this type, that is gateways not integrated in the sensor, usually have fixed identification numbers in the respective communications system and also appear directly as a gateway with respect to the fieldbus. A sensor connected to the gateway, in contrast, cannot be addressed directly from the fieldbus, but rather only via the gateway.
Different data packets, so-called objects, can be transmitted to the fieldbus from a sensor. Objects of this type can, in a temperature sensor for example, be the current temperature or the maximum value of the respective measured temperatures.
Previously used gateways can only transmit specific, fixedly predetermined objects between the sensor and the fieldbus. This can be imagined in figurative terms such that fixedly predetermined “shelves” are present in a gateway and the objects of the sensor can be placed onto them from where they can be “collected” by the fieldbus. However, this only works for those objects for which a suitable “pigeonhole” is present. Objects for which no suitable “pigeonhole” is present cannot be transmitted to the fieldbus, which ultimately means that only a limited operation of the sensor is available to the fieldbus in a disadvantageous manner.
This disadvantage can only be eliminated in a complex and/or expensive manner in that fieldbus gateways are provided adapted to each sensor type which are in a position to transmit all the objects of a sensor to the fieldbus.