Patent Publication Number: US-2007116133-A1

Title: Automation device

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims priority from German Application DE 10 2005 043 481.9 filed on Sep. 13, 2005 the contents of which are relied upon and incorporated herein by reference in their entirety, and the benefit of priority under 35 U.S.C. 119 is hereby claimed.  
     BACKGROUND OF THE INVENTION  
      The invention relates to an automation device, with which a multiplicity of physically distributed functional units communicate with each other by means of a common transmission protocol. These functional units manifest themselves as field devices or operator units according to their automation function.  
      For some time now it has been common practice in instrumentation and control engineering to use a two-wire line to supply a field device and to transfer measurements from this field device to a display device and/or to an automation control system, or transfer control values from an automation control system to the field device. Each measurement or control value is converted into a proportional DC current, which is superimposed on the DC supply current, where the DC current representing the measurement or control value can be a multiple of the DC supply current. Thus the supply current consumption of the field device is usually set to approximately 4 mA, and the dynamic range of the measurement or control value is mapped onto currents between 0 and 16 mA, so that the known 4 to 20 mA current loop can be used.  
      More recent field devices also feature universal properties that are largely adaptable to the given process. For this purpose, an AC transmission path capable of bi-directional operation is provided in parallel with the unidirectional DC transmission path, via which parameterization data are transferred in the direction to the field device and measurements and status data are transferred from the direction of the field device. The parameterization data and the measurements and status data are modulated on an AC voltage, preferably frequency modulated.  
      In process control engineering, it is common in the field area as it is called, to arrange and link field devices, i.e. measurement, control and display modules, locally according to the specified safety requirements. These field devices have analog and digital interfaces for data transfer between them, where data transfer takes place via the supply lines of the power supply arranged in the control area. Operator units are also provided in the control area, as it is called, for controlling and diagnosing these field devices remotely, where lower safety requirements normally apply.  
      Data transfer between the operator units in the control area and the field devices is implemented using FSK modulation (Frequency Shift Keying) superimposed on the known 20 mA current loops, where two frequencies, assigned to the binary states “0” and “1”, are transferred in frames as analog signals.  
      The general conditions for the FSK signal and the type of modulation are specified in the “HART Physical Layer Specification Revision 7.1-Final” dated 20 Jun. 1990 (Rosemount Document no. D8900097; Revision B).  
      ASICs specifically developed to implement the FSK interface according to the HART protocol, such as the HT2012 from the SMAR company, are commercially available and in common use. The disadvantage with these special circuits is the permanently fixed range of functions and the associated lack of flexibility to adapt to changing requirements.  
      Known modern automation devices are usually equipped with a processing unit known as a microcontroller, which is used to perform the correct data processing for the automation task of the functional unit concerned.  
      The aim is to reproduce the functions of the FSK interface according to the HART protocol in the controller of the processing unit of the automation devices, without impairing in the process the automation task of the functional unit concerned.  
     SUMMARY OF THE INVENTION  
      Hence the object of the invention is specifically to define an automation device having means for converting an FSK signal into a data bit-stream using a microcontroller known per se.  
      The invention is based on an automation device having a processing unit, which is assigned at least one memory unit for storing instructions and data. Connected to this processing unit on the transmit side is a digital-to-analog converter whose output is connected to a filter.  
      To reconstruct the transmitted data bit-stream from the FSK-modulated line signal, an event-controlled counter is provided. At each zero crossover of the line signal, the counter reading of the counter is buffer-stored and the counter is restarted.  
      The frequency representing the elapsed half-wave is detected from the time interval between two consecutive zero crossovers, which is registered by the buffer-stored counter reading, and the associated bit value is output. For this purpose, at each zero crossover of the line signal, an interrupt request is triggered, following which program execution of the microcontroller is interrupted. After the reconstructed data bit has been output, program execution of the microcontroller is recommenced and continued at the interruption point. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The invention is explained in more detail below with reference to an exemplary embodiment. In the drawings required for this,  
      FIGURE  1  shows a block diagram of an automation device.  
      FIGURE  1  shows schematically an automation device  100  to the extent necessary to understand the present invention. 
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS  
      The automation device  100  is connected via a communications line  200  to an automation device  100 ′ of substantially the same type. The communications line  200  is used bi-directionally. The information sent by the automation device  100  is received by the automation device  100 ′, and vice versa. Hence reference is only made below to the automation device  100  shown in detail.  
      A core component of the automation device  100  is a controller  110 , which is connected at least to one memory unit  150  and one timing element, referred to below as a clock generator  120  for the sake of simplicity. Usually, however, parts of the clock generator  120  are already implemented in the controller  110 .  
      The controller  110  has connections for connecting a data sink  130  and a data source  140 .  
      A configurable and/or parameterizable sensor for converting a physical variable into an electrical variable can be provided as the data source  140 , in which case the configuration and/or parameterization is the data sink  130 .  
      In an alternative embodiment, it can be provided that the data sink  130  is an actuator for converting an electrical variable into a physical variable whose properties can be diagnosed. The diagnostic device provided for this purpose is then the data source  140 .  
      In a further embodiment, it can be provided that the automation device  100  is part of a higher-level device designed for bi-directional communication with additional automation devices  100 ′. In this embodiment, the higher-level device is both the data source  140  and the data sink  130 .  
      In a further embodiment, the automation device  100  can be designed as a “protocol converter”. In this embodiment, the data source  140  and the data sink  130  are formed by a second communications system.  
      To implement the invention, however, it is sufficient for the data source  140  to be present without the data sink  130 .  
      In addition, connected to the controller  110  is a digital-to-analog converter  160  whose output is connected to a filter  170 . The output of the filter  170  is connected to the communications line  200 . In addition, the communications line  200  is taken to the input terminals of the controller  110 , via which terminals it is provided that the line signal  201  on the communications line  200  is received.  
      Starting from the communications line  200 , the automation device has a demodulation device  180  at the receiver end. The demodulation device  180  essentially comprises a zero-crossover detector for detecting the zero crossover of the line signal. The output of the zero-crossover detector is connected to an interrupt input of the microcontroller.  
      To reconstruct the transmitted data bit-stream at the receiver end from the FSK-modulated line signal, an event-controlled counter is provided.  
      At each zero crossover of the line signal, an interrupt request is triggered, following which program execution of the microcontroller is interrupted. Program execution of the microcontroller is then branched to an interrupt processing routine. In this interrupt processing routine, the current counter reading of the counter is read out and buffer-stored. Then the counter is reset and started again.  
      The frequency representing the elapsed half-wave is detected from the time interval between two consecutive zero crossovers, which is registered by the buffer-stored counter reading, and the associated bit value output. After the reconstructed data bit has been output, program execution of the microcontroller is recommenced and continued at the interruption point.  
      According to a further feature of the invention, a filter is connected to the input of the zero-crossover detector, thereby removing interference signals from the line signal.