How can I bypass a potentiometer that feeds into a drive controller by using an SCC-AO10 module? Which wires must I cut and where should they connect to the SCC-AO10 module?

[saspe]

I am trying to bypass a potentiometer that controls a wind tunnel DC motor. The potentiometer (10 kohm) has a greeen wire (+10V) a blue wire (ground) and a red wire (AI1 voltage, 0-10 V). These three wires feed into an ABB mounted drive controller that somehow converts the 3-phase (220-240V) power to a signal for the DC motor in the wind tunnel. I want to make a velocity control loop for the wind tunnel speed in Labview and I must bypass the potentiometer. If I am planning to use a PID that equates a measured velocity to the setpoint velocity, how can I get a output signal from my SCC-AO10 to the drive controller? I have been asked to use a switch that would allow the potentiometer to be used or the automatic control loop in Labview. Which wires will I need to cut from the potentiometer and where will I have to connect them on the SCC-AO10?

Has anybody done this and the PID for a wind tunnel motor? Please help me if you can.

[DjDaveNI]

Hello saspe,

What are the voltage/current requirements for the drive controller you mention? The SCC-AO10 module can source ±10 V with a maximum current drive of ±30 mA (see page 7 of the manual).

As for wiring instructions, check out pages 4-5 of the manual.

What version of the LabVIEW software are you using? How about the PID toolkit and NI-DAQmx drivers? What other NI hardware are you using in your setup (SCC backplane, and PCI DAQ card)? This info will help us further understand exactly how you have everything set up.

I hope this helps 🙂

[saspe]

DjDave,

Thanks for looking out. We have a PCI-6251 connected to a SC-2345 box. In the box we are taking temperature and pressure measurements from the wind tunnel for the velocity measurement with a TC02 and a AI04. The windtunnel has a control panel where the ABB drive controller connects the 3-phase to the wind tunnel motor. The controller has a +10V reference voltage, an output frequency reference (0...10V), and a ground that feed from the potentiometer. The controller also has a +24V (max. 200mA) auxiliary voltage output which appears to drive the motor. From what I understand, the potentiometer's position is the function (output frequency reference). We eventually want to make a velocity setpoint input in Labview that will drive the motor accordingly. I am guessing the best way is to make use of the controller. I was wondering if you could help me figure out the cable connections necessary to bypass the potentiometer and generate a signal from Labview that will drive the motor. Again the 3 cables from the potentiometer are: greeen wire (+10V), blue wire (ground) and red wire (AI1 voltage, 0...10 V). I have seen that the SCC-AO10 needs a ground and the positive lead wire. I am not sure how this compares to how the potentiometer is connected.

We are using Labview 8.2.

Cheers.

[DjDaveNI]

Hey saspe,

Can you post the model numbers and manufacturers of both the potentiometer and the drive controller? Even better, links to the online manuals for both. This way we can see the signal specifications for each wire, and completely understand the setup.

Cheers!

[saspe]

DjDave,

Sorry I've been away for a while..I'm back in the lab now and ready to get this working!

Our drive controller is ABB ACS350. the manual is at http://www.state-electric.com/files/manuals/abb/ACS350-Operations-Manual.pdf and the connections diagram is on page 87.

The potentiometer is a 10 kohm Vishay Spectrol #533-1-1, the data sheet is at http://www.vishay.com/docs/57065/533534.pdf and it has red (to port 2 of ABB controller), blue (to port 3 of ABB controller)and green (to port 4 of ABB controller) wires.

Let me know if this is enough info, and thanks for your attention!

[ST5 · Accepted solution]

"The potentiometer (10 kohm) hasThe potentiometer (10 kohm) has a greeen wire (+10V) a blue wire (ground) and a red wire (AI1 voltage, 0-10 V). a greeen wire (+10V) a blue wire (ground) and a red wire (AI1 voltage, 0-10 V)."

So you unwire the +10V and ground.

The drive reacts to the voltage input (0-10V)

Simply connect this red wire to your analog output module, and connect ground (blue) to the ground of your module.

. 

[Kristen_K.]

Hi saspe!

According to the SCC-AO10 User Guide (page 4), to connect the SCC-AO10 to the drive controller you will need to connect as follows:

- blue ground wire from the drive controller to pin 1 (bottom-most) on the SCC-AO10
- red AO wire from the drive controller to pin 3 (top-most) on the SCC-AO10

As far as being able to switch back and forth between using the potentiometer and the DAQ board + LabVIEW, it's possible a switch could be designed to accomodate this.  However, because the potentiometer has high impedience, it could alter the DAQ signal.  I would recommend just switching the wires back and forth to avoid this issue.  I hope this helps.


Kristen H.

[saspe]

Thanks ST5 and Kristen!! I will try that. Sounds pretty simple, but I'm glad I asked cuz I was afraid of shorting something or having the motor go crazy on me.

[Henrik_Volkers]

Some more thoughts about switching between manual potentiometer and your LabVIEW application:

What will happen at any time at any setting when a bad terrorist (or untrained/sleepy operator) toggle the switch?

Ideas: How about a pot with a switch, so at least the manual input is savely zero while switching.

Or use additional circuitry to always use the minimum of the two (manual and 'LabVIEW') voltages....

[saspe]

Great! The module it now on its way, and I've checked that the impedence is not surpassed at the max setting. I'm not very fresh on my electrical circuit design....so what circuit would be necessary to always take the lower of the two signals (potentiometer or module)? Any examples that may help me visualize it?

Thanks a lot for the advice guys/gals!! I think we're impressing my supervisors with this team effort!! kudos!