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Using PXI 7352 Motion card and 6025E DAQ
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11-29-2004 01:17 AM
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Dear Sir,
I am using SCXI 1520 along with PXI 1011 & E Series DAQ (6025E) to measure the Load Value of a load cell. I am also using PXI 7352 Motion card to control the velocity of a Plunger. Now my requirement is to stop the movement of the Plunger depending on the value I read from the load cell. I am not able to achieve the stoping accuracy for high speeds (around 150mm/sec) in the software. Can it be possible with the use of Motion Control card and RTSI signals? If so, how can I do that? (I am not used any limit switches as the load value at which the Plunger should stop is user programmable and I am using DAQ card in Multiplexed mode because i am reading more number of analog inputs with only one DAQ card)
Ramkumar. D
Soliton Automation,
India.
I am using SCXI 1520 along with PXI 1011 & E Series DAQ (6025E) to measure the Load Value of a load cell. I am also using PXI 7352 Motion card to control the velocity of a Plunger. Now my requirement is to stop the movement of the Plunger depending on the value I read from the load cell. I am not able to achieve the stoping accuracy for high speeds (around 150mm/sec) in the software. Can it be possible with the use of Motion Control card and RTSI signals? If so, how can I do that? (I am not used any limit switches as the load value at which the Plunger should stop is user programmable and I am using DAQ card in Multiplexed mode because i am reading more number of analog inputs with only one DAQ card)
Ramkumar. D
Soliton Automation,
India.
ColinAE
NI Employee (retired)
11-30-2004 11:43 AM
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Hello.
Based on your post I am guessing that you are performing the control in software, i.e. starting a velocity move, and then reading the load cell until it reaches a threshold, then stopping the motion. As such you are essentially limited by the software control loop rates.
You are using PXI so it is possible that you are using real-time. If not, one solution could be to implement a real-time application that would be more deterministic, but again this would still depend on the software.
Depending on your system (stepper or servo), you could implement a direct analog feedback into the motion card itself, but this would require a signal which has a range much greater than your load cells. This is only a good option for servo axes. If this was somehow possible, you can tell the motion controller to move to a specified LOAD instead of a specified position/velocity. Provided you could appropriately condition the signal, this is the best choice.
Unfortunately, you cannot implement limit switches/etc over RTSI, so I believe that this will not be a good option.
A third, and probably most un-desireable option, is to output a voltage on the PXI-6025E proportional to the load received from the load cell. This voltage could then be used as the analog feedback for your motion device. This, however, still adds the software layer of delays.
I hope these ideas help you out.
Regards,
Colin C.
Applications Engineering
Based on your post I am guessing that you are performing the control in software, i.e. starting a velocity move, and then reading the load cell until it reaches a threshold, then stopping the motion. As such you are essentially limited by the software control loop rates.
You are using PXI so it is possible that you are using real-time. If not, one solution could be to implement a real-time application that would be more deterministic, but again this would still depend on the software.
Depending on your system (stepper or servo), you could implement a direct analog feedback into the motion card itself, but this would require a signal which has a range much greater than your load cells. This is only a good option for servo axes. If this was somehow possible, you can tell the motion controller to move to a specified LOAD instead of a specified position/velocity. Provided you could appropriately condition the signal, this is the best choice.
Unfortunately, you cannot implement limit switches/etc over RTSI, so I believe that this will not be a good option.
A third, and probably most un-desireable option, is to output a voltage on the PXI-6025E proportional to the load received from the load cell. This voltage could then be used as the analog feedback for your motion device. This, however, still adds the software layer of delays.
I hope these ideas help you out.
Regards,
Colin C.
Applications Engineering
Project Support
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12-03-2004 02:18 AM
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Dear Colin,
We like your suggestion of providing a direct analog feedback into the motion control card. The load cells signals are conditioned using the SCXI 1520. Is there any way of tapping the signal conditioned output say from the SCXI back plane? If we can do this, then this is a viable solution.
I am expecting your early reply.
Thanks,
Ramkumar. D
Soliton Technologies.
We like your suggestion of providing a direct analog feedback into the motion control card. The load cells signals are conditioned using the SCXI 1520. Is there any way of tapping the signal conditioned output say from the SCXI back plane? If we can do this, then this is a viable solution.
I am expecting your early reply.
Thanks,
Ramkumar. D
Soliton Technologies.
ColinAE
NI Employee (retired)
12-03-2004 03:13 PM
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Hello.
Unfortunately, the solution you suggested (tapping into signals from SCXI-1520) is not a supported option. There is a possibility that you would be able to tap into the signals by capturing the analog data going to the 6025E through the cable, but unfortunately, this is not something I could help you with the details, as it would void warannties and is not supported.
Just to give you a high level idea, if you are running the 1520 in parallel mode, then each channel is placed on the equivalent differential channel of the 6025E (i.e. channel 0 goes to ACH0 and ACH8, etc). You could tap into those signals and wire those to the motion board's ADC inputs, and then use that as feedback.
Regards,
Colin C.
Applications Engineering
Unfortunately, the solution you suggested (tapping into signals from SCXI-1520) is not a supported option. There is a possibility that you would be able to tap into the signals by capturing the analog data going to the 6025E through the cable, but unfortunately, this is not something I could help you with the details, as it would void warannties and is not supported.
Just to give you a high level idea, if you are running the 1520 in parallel mode, then each channel is placed on the equivalent differential channel of the 6025E (i.e. channel 0 goes to ACH0 and ACH8, etc). You could tap into those signals and wire those to the motion board's ADC inputs, and then use that as feedback.
Regards,
Colin C.
Applications Engineering
Project Support
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01-03-2005 07:48 AM
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Dear Colin,
I have one issue regarding SCXI 1520 when using with PXI 1011 combined chassie. How can i configure one single channel for simple voltage measurement while using the other seven channels for strain gauge inputs?
This is because i am using an external amplifier to take a parallel output for my motion control card PXI 7352. This amplifier exites the load cell and amplifies the output from it which is routed to one of the analog input channels of the motion control card (and also this data is logged through SCXI 1520 unit).
What are the things i should take care if i go for external excitation rather than from SCXI 1520?
Kindly help me regarding this.(kindly reply me through ramkumard1981@yahoo.com as i am in remote place).
Thanks,
Ramkumar. D
Soliton Technologies.
I have one issue regarding SCXI 1520 when using with PXI 1011 combined chassie. How can i configure one single channel for simple voltage measurement while using the other seven channels for strain gauge inputs?
This is because i am using an external amplifier to take a parallel output for my motion control card PXI 7352. This amplifier exites the load cell and amplifies the output from it which is routed to one of the analog input channels of the motion control card (and also this data is logged through SCXI 1520 unit).
What are the things i should take care if i go for external excitation rather than from SCXI 1520?
Kindly help me regarding this.(kindly reply me through ramkumard1981@yahoo.com as i am in remote place).
Thanks,
Ramkumar. D
Soliton Technologies.
