@Rene:
My solution using the ActiveX OCX was not pretty, but it worked for a test stand project. A screen shot is attached. There was a problem between the LV Client and the Beckhoff server with arrays. My understanding was that LV interpretted the interface to pass a single data value. My solution was to store an array as a waveform on the PLC. The array was stored with an element size of the A/D conversion size, I16. I then requested each element as a double value and decoded into the four elements. The PLC waveform also included its scaling factor, dY, similar to the LabVIEW dt scaling factor for the time data.
The LV program also had a calibration routine to scale the A/D voltage values (0..10 V) into engineering units according to the customers calibration equipment.
This example was written 4 years ago and I understand that the array interface between LV and TC was resolved in LV 8.5.
in "TC_LV Waveform Acquire OCX.jpg", the ADS address (index & offset) are defined in the program as constants. The PLC waveform includes elements similar to LV waveforms. The PLC Waveform elements are:
t0 - initial timestamp of acquisition
dt - PLC scan time of DAQ task
dy - PLC scaling factor for waveform
nData - number of elements stored in the array
data - array of (raw) Int16 data, maximum size = 10000
The subVI reads the first four scalars and then loops to transfer each data element. The Int16 size was chosen to minimize data length. Reading doubles for each element of the array results in four Int16 elements. However, the must be extracted from the 8-byte double.
The subVI, "TC_LV Waveform Conversion.JPG", performs a conversion from the PLC Waveform cluster to a LV waveform in order to use native waveform functions in LV.
Regards,
Kenneth
p.s. In my VI, I had implemented the array transfer and conversion in several ways, including methods that only transferred a single value (the built-in array) methods. I have not retested those other solutions with the latest LV-TwinCAT versions.
