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Answered

Bi-Directional vs Uni-directional Cout Saturation

Derek Lagrainge 3 years ago in IQANdesign updated by Gustav Widén (System support) 3 years ago 1

In my fan system we have a gear pump feeding our fan valve which feeds a gear motor. The initial programmer had it set as "Bidirectional: YES" and the positive direction values were as follows:


Min Current: 605 mA

Max Current: 0 mA

Start slope/Stop slope: 250 ms


(The negative direction is just opposite of that, Min: 0, Max: 650)


The valve is programmed to open (allow the fan to go full on, therefore max oil flow) at 0 mA, and otherwise programmed to run according to the cooling demands. But there is no actual negative direction, it is a proportional valve, it's either (somewhat) open or closed so it's 0 to 650.


Sometimes when it's hot outside, the hydraulic oil gets hot and the coil (probably) heats up we get a "FAN SPEED COUT SATURATION" error a few seconds after starting up the machine again. I did some testing and found that if I eliminated the Bidirectional component and made it unidirectional that this problem goes away. It makes sense in my mind as the valve is proportional so why should the program ever look for a negative direction.


Does my logic make sense? Would you ever need a bidirectional Cout for a proportional valve?


Sorry for the long rambling post.

Answered

You would normally only use the COUT as bidirectional when controlling a proportional directional valve, for example the Parker L90LS.


For controlling the speed of a fan motor when you only have one coil that is proportional, it makes more sense to set Bidirectional=No.


But this has nothing to do with saturation, the COUT is saturated when the commanded current is higher than what can physically be achieved. This depends on the available supply voltage (+BAT), the load characteristics (coil resistance increase with temperature), the voltage drop over the IQAN module and the maximum modulation ratio at the set dither frequency.


To avoid the saturation warning, you could try to decrease the commanded current, and see if you are still able to get the same result as before.


It is worth noting that in version 4.03, the logging of the saturation warning was removed. The COUT status will still indicate if the output is saturated, but it won't be written as an event in the system log.

http://divapps.parker.com/divapps/iqan/Downloads/IQANdesign%204/ReleaseNotes4.03.27.htm


It was interesting to see that you have the min current set to a value above the max current, I did not know that this worked as a method for inverting the output, but apparently it does. It does give a project check warning saying "Max needs to be greater than Min"

I have always inverted the command in the math function that is used as input to the COUT instead, like in this solution library example:

\Documents\IQAN Files\Solution Library\Fan drive -simple.ids4


What I think you should consider changing is the 0 mA parameter. The specified minim current the COUT can control is 100 mA, if you try to drive a current that is much lower than this, you can get into a situation where the COUT becomes unstable, and switches off with the status open- or overload.