reverse direction of analog feedback

[wayne g]

Dear All

I have a motion system, where I switch between position control (encoder) and load control (analog feedback).  I have many transducers that are wired and to use on the system.

My problem is, that when in analog feedback, the transducers drive the motor the wrong direction and thus without any control as the system becomes unstable.  If I simply swap the output signal from the transducer the system works fine.

Is there a way that I can do this in software either Labview or MAX.  I have not been able to find how and it is not a simple switch of polarity as the system is controlled at a low level by the PID parameters

Thanks for any help and I hope this question makes sense.

wayne

[Marni]

Hello Wayne,

What hardware are you using?

What kind of signal are you reading in?

What are you currently doing in software that drives the motor the wrong way?

Have a great day!

Marni S.

[wayne g]

Marni

I am reading a load cell and driving a motor based on that.  The problem that I am having is that the motor drives the opposite way to the feedback - this I thought would be a relatively simple swap of some setup bit and get on with it.  I have though had an email from NI in Germany - Jochen Klier, who stated that it is not possible to achieve what I am after.

As such, I had already thought about having to make an inline cross-over plug that would simply reverse the signals on the transducer without having to rewire the transducers.

The hardware I am using is both the PCI 7344 and PCI 7354 motion control card. 

I must also apologise for my post ending up on the signal conditioning group.  It seems that firstly the email was deleted then sent to the incorrect list.

wayne

[nipun]

Hi wayne,

I don't see any way of swapping the polarity of the analog feedback or the PID output in software. Is there a reason why swapping the hardware lines is a problem for this applications?

Regards,

Nipun M

Applications Engineer

Motion and Vision Group

National Instruments

[wayne g]

Nipun

There is no real problem with swapping the signal lines in our transducers, as mentioned earlier by way of an inline plug will achieve this. 

I was just thinking that if I could achieve it in software then I would. 

wayne

[nipun]

Hi wayne,

I've been looking for possibilities, but unfortunately don't see any viable way of achieving this in software. I was concerned if this is a remote system that might make it difficult for you.

Regards,

Nipun  

[Henrik_Volkers]

IF you read the sensor with a custom channel , created in MAX , why it's not possible to change the sign?

Isn't it possible to enter a negativ m (-1) in the custom linear scaling?

[AnalogKid2DigitalMan]

Another option may be if you had a spare digital output to fire a double pole double throw relay (DPDT) you could have the relay swap the polarity