Posted 13 Aug 2011 I am not very knowledgeable about Siemens but know enough to get around and do a few changes. My question is a couple of days ago I had a drive that stopped working on a system. After checking all hardware, I noticed that the main power relay would not pull in and the enable to the drive would not come on. No faults in the system as I could tell. I went online with the PLC and back traced to the FC block that was triggering the drive contactor and enable output. The trigger was a set of inputs in a & statement that triggered the drive. In the FC block the bits were turning on the off triggering a set and reset bit so as soon as the set was done the reset occurred and never triggered the drive relay, but the inputs that triggered the bits were solid. Thinking there was a wiring issue I check voltage and have a steady 24VDC to the inputs I then though that maybe the card was bad so I changed the inputs in the code to an input that was not used and put 24VDC to the input. We I looked at the FC block it was doing the same thing as before, the FC block bit was turning on then off and the inputs that triggered the bit were steady. With all the hardware and the wiring checked and good I am very confused as to why this is happening. Hope this makes sense and if anyone could give be something to look at further that would be great. Share this post Link to post Share on other sites
Posted 14 Aug 2011 1. How many times is this block called in the software, if more than once then you may not be seeing true data when you are monitoring the block. 2. May help to paste some screen shots of the code in question, include the call, the io parameters and the code. Share this post Link to post Share on other sites
Posted 14 Aug 2011 It looks like it is call twice in the program there are two identical drive on this system and each one is enabled by this FC Block. I will try and get some screen shot on Tuesday when I am Back in. Share this post Link to post Share on other sites
Posted 14 Aug 2011 FC's should not really be used in this way, they can be but make fault finding more difficult, you have to revert to looking at memory areas to try to see what is going on. If they are called from different FC's, then it is possible to monitor via a path which means you can see real data. FB's are better because you can also stipulate the DB, therefore you would state the IDB that bel;ongs to the FB. Share this post Link to post Share on other sites
Posted 16 Aug 2011 (edited) Make copy of the FC, change other call to that FC. Then you can monitor it. Edited 16 Aug 2011 by muotioj Share this post Link to post Share on other sites
Posted 16 Aug 2011 (edited) This is a possibility but maybe not necessary if the block is called from different blocks, because there is a mode where you can specify a path to the block that you need to monitor. Edited 16 Aug 2011 by Groo Share this post Link to post Share on other sites