DF Profi II Zeros Problem

[Mattia88]

Hello everyone,

i have a problem with a DF Profi II board, a Comsoft product made for profibus networking. I'm using a PXI 8110 with the board installed, and labview 2013 (the PXI as real time target and my PC as host). Everything works well and i am able to acquire from the profibus network (PXI is the slave and a Numerical Control of a Milling Machine is the master); the only problem is that, quite frequently at random time stamps, the board gives a 0 for each channel i'm acquiring.

Thanks and best regards.

Mattia

[Jesse_D]

Hi Mattia, 

Can you log the data you are getting and post it? How frequently is frequently? What is your cycle time? 

Immediately, I would guess electrical interference. Profibus tends to be very sensitive to the proper termination, you might check everything is bolted tight. 

Also, depending on how big the machine you are controlling is EMI may be a consideration. How big is this mill? 

[Mattia88]

Thank you Jesse, i really appreciate.. 

I have tested different values of the cycle time, from a minimum of 10 milliseconds up to 500 milliseconds but the problem doesn't seem to be solved. I am acquiring with the labview functions given by the Comsoft library with the following settings:

- baud rate 1500 kBit/sec

- slave modules 240 byte-inp / 240 byte-out

Unfortunately  i'm not able to give you some data right now, but with frequently i meant something like every second or more. The machine is a 4 axis machining center with an horizontal spindle (65 kW) equipped with a Siemens 840D numerical control.

Besides, i will try to check the network as you've suggested,

Thanks for the support.

[Mattia88]

Ok, i'm posting 3 acquisitions of a profibus channel (time costant x-axis position) made with differetn cycle times.

Hope it'll be useful.

Thanks

[Jesse_D]

I notice in each of the log files you see zeros at some multiple of your cycle time. At 1500kB/sec I expect it to take around 1.3ms to updated your data. If you tried to read data while the master was updating it you might see weird behavior.  Also check all your error and statuses on the slave, you might be returning a code and just ignoring it. 

Try seeing if your master supports consistency: 

What is Data Consistency 
If a data format is selected that requires full data consistency, this 
guarantees that the data on the Profibus is not updated with the new 
data values until ALL data words have been written into the Profibus 
buffer memory. 
Consistent data may be important when using the 4-word non-cyclic 
data format. Without consistency, it is possible for 2 of the 4 words to 
go on one network cycle, with the data value updated on the next cycle. 
If the command was a write command, this could result in the previous 
data value being written to the new parameter, and could have 
disastrous consequences. 
Using data consistency can often put restrictions on data manipulation 
within the master controller, and may require the use of special 
functions within the master controller, and these can take longer to 
execute. (Consult the supplier of the master controller for further 
information

or try increasing your baud rate. 

[Mattia88]

Thank you for the advices Jesse, i'll let you know after some tries.