Baud rate of NI-cDAQ 9174

[NomisG]

Hello all, 

Is it possible to change baud rate for serial communication between NI-cDAQ 9174 and PC or is it problem with my computer because sometimes i get interruption. I am using NI 9239 to measure voltage from LVDT sensor.

Thank you for your help

Best regards

[GerdW]

Hi Nomis,

how is the cDAQ9174 connected to your host computer?

How does the NI9239 come into play when asking about "serial communication"?

[NomisG]

Hi GerdW,

Thank you for your reply. It is connected with standard USB cable.What do you mean with that last question? It is connected into first sloth of cDAQ9174.

Best regards

[GerdW]

Hi Nomis,

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@NomisG wrote:

Thank you for your reply. It is connected with standard USB cable.

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You cannot change speed (aka baudrate) of a USB connection…

What exactly is your problem with cDAQ-to-host connection?

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@NomisG wrote:

What do you mean with that last question? It is connected into first sloth of cDAQ9174.

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So the information on the NI9239 is irrelevant for your problem…

[NomisG]

Hi GerdW,

I am using LVDT sensor for measuring displacement of a actuator that is moving from one to other position. This is done by setting start and end position of actuator. I am also reading current position of actuator and sometime it overshoots and I am reaserching what could be the problem. Maybe data is missed sometimes or it is something else (maybe sensor is the problem). I think that electronics part it is fast enough to do that.

I hope now it is more clear.

Best regards

[GerdW]

Hi Nomis,

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@NomisG wrote:

This is done by setting start and end position of actuator. I am also reading current position of actuator and sometime it overshoots and I am reaserching what could be the problem.

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Does the actuator reach its end position even when it overshoots?

How is the actuator controlled?

[NomisG]

Hi GerdW,

The actuator is controlled by H bridge mosfet transistors. National instrument  digital output card drives those transistors. Yes everytime it reaches problem happens with higher frequency.

Best regards

[GerdW]

Hi Nomis,

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@NomisG wrote:

The actuator is controlled by H bridge mosfet transistors. National instrument  digital output card drives those transistors.

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Apparently there is a lag in your control loop between AI (reading of position sensor) and DO (driving the H bridge/actuator) which introduces those overshoots. Or the controller is not properly tuned…

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@NomisG wrote:

problem happens with higher frequency.

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Please define "higher frequency"…

[NomisG]

Hi GerdW

Yes that are thoughts, Like it works fine on 2Hz and then I change to 3Hz displacment changes for 1 mm something like that. I general that is not much but for measurment is something. I was thinking trying with CompactRIO it has its own processor. 

I dont know if I described it before but when you open like a browser on a computer while running control it lags.

Best regards

[NomisG]

I have set in DAQ assistant :

Samples to read: 1

Rate (Hz) : 1kHz

I just checked switching time from electronics from low to high is like 700ns.

Best regards