Beckhoff has now developed an oscilloscope Bus Terminal with a trigger
input for decentralized pre-processing of fast analog values. The digital result can then
be transmitted, at lower speed, to higher level automation devices, where they can be used
for control purposes. The advantage is that the image provided by the fast data
pre-processing can record limits, maximum and minimum values. A large number of signals
could, for example, find the compression force of an eccentric coin press, and thus obtain
indications of the resulting quality.
The trick with the trigger: Get fast signals safely read before secure transmission
Selected information instead of a
flood of data
There are a number of ways to initiate the trigger: triggering may be initiated by a
threshold signal, by an external trigger input, or by a bit in the process image. All
three kinds of triggering solve one and the same problem: a specified group of
measurements is recorded in place of a data flood. This gives the automation engineer an
ideal way around the bottleneck that a fieldbus can present. The transmission of data over
conventional fieldbusses can quickly hit a ceiling if a large number of analog values have
to be transferred at high speed. Such processes can often take 1 ms or longer. The central
computer handling the control tasks, on the other hand, can reliably perform its processes
at a higher rate. The KL3361 input terminal's trigger input allows fast analog values to
be decentrally pre-processed. The inputs also allow a resistance measuring bridge (strain
gauge) with 10 V and 100 mV inputs to be connected. For that matter, any combination of
other voltage levels may also be used. The input values are digitized with a resolution of
16 bits, and stored in internal memory. A powerful processor can access them, process the
values, and then read them at lower speed out of the memory, transferring them to a higher
level.
Because the recording of the data can now be reliably synchronized, the Bus Terminal can determine limits, record maximum and minimum values, and can monitor envelopes. These values are reported to the higher level computer, which can use them for its process control operations.
A practical example illustrates the benefit: the compression force determines the
quality of the stamping in coin manufacture. The eccentric can provide the Oscilloscope
Bus Terminal with the trigger pulse for recording the measurements. The control system can
evaluate, on the basis of the measured compression force, whether the stamping quality is
adequate. The time-consuming inspection of every single coin becomes unnecessary. But the
advantages of the KL3361 are not restricted to stamping presses. The principle of fast
data pre-processing is also applicable to the production of tablets or other equally fast
processes.
Measuring overshoots
The KL3361 is not just able to read in data at high speed, but can control and monitor
processes itself. Exceeding maximum or minimum values can easily be used for fast shut
down. The trigger threshold is set at the corresponding value, and the occurrence of the
trigger event is indicated via the 24 V output. The processing takes place in less than
100 µs. This is much faster than would currently be possible over a fieldbus.
Other functions integrated into the terminal permit valuable information from the application to be acquired quickly and easily. The KL3361 finds the height of the overshoot by means of two simple functions: Us and Umax histo.
