Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00

We experienced a problem with the revision of the Danfoss software in the VLT3000 which meant that a particular unit dropped off line for quite substantial lengths of time. This is a recognized bug in the Danfoss version 2 software - you need to use Danfoss version 3 software (This involves getting the latest control card - that is the entire control card PLUS profibus option card, not just the Profibus option card, on Version 3).

When the Profibus control word is used to start or stop the drive, please note that it is not possible to have a totally parallel method of control such as digital inputs onto the control card in the VLT3000. This is because the control word uses a non-latch type of control, ie. you set a bit to one and the drive runs, you set a bit to zero and the drive stops. There are combinations which allow alternative control points but the best we could come up with (after lengthy consultation with Danfoss), was a system which meant that wherever you stopped the drive from, you had to restart it from. This was using Profibus control and digital inputs onto the card which came from pushbuttons in the field. If two points of control are required, I recommend that the start/stop control be performed through a PLC.

Also we came across the problem of changing speed setpoints, which is done through Profibus by changing the bus reference for each drive. They had a field setup which involved turning a switch to the right to jog up the speed and to the left to jog down the speed - the way that this was achieved in the VLT3000 was to configure 3 digital inputs - one for jog up, one for jog down and one for freeze reference. The freeze reference input holds the bus reference so that the jog up & down functions are activated - as soon as the freeze reference is turned off, the 'jogged' speed reverts to the bus reference. Thus in this case they needed to keep the freeze reference turned on to retain any field changes made to the speed. This also precluded Citect from changing the speed, since the bus reference was frozen with the freeze reference input. We could not work around this so it was decided to only have the operators able to change the speeds in the field, from the pushbuttons. This is a limitation of the Danfoss VLT setup. There may be other ways of configuring the drive for external speed changes but this particular way is not very useful if Citect needs to change the speeds.