Read ticks from encoder

[AndrzejS]

Hello,

I have problem with reading position from encoder (encoder is a part of ThorLabs DCMotor).
I've connected it to my NI USB-6259 based on information from page: http://zone.ni.com/devzone/cda/tut/p/id/7109#toc1

I created CIAngEncoderChan and after starting the task I tried to read value from encoder.
I've obtained the error massage:
-200378 Custom scale specified not exist.
Do I make something wrong?

I'm using a code which part is bellow:
DAQmxErrChk DAQmxCreateCIAngEncoderChan(taskHandleCont, "Dev1/ctr0", "", DAQmx_Val_EncoderType2_X4, False, 0, DAQmx_Val_EncoderZIndexPhase1_AHighBLow, DAQmx_Val_LengthUnits3_Ticks, 29, 0, ByVal 0&)

DAQmxErrChk DAQmxStartTask(taskHandleCont)
   
While taskIsRunningCont = True
    DAQmxErrChk DAQmxReadCounterF64(taskHandleCont, 10000, 10, dataH, 10000, dataL,         ByVal 0&)
    countTextBox.Text = Conversion.CStr(dataL)
    DoEvents
 Wend

Any suggestions?????

Thanks,
AndrzejS

[Stefo]

Hi Andrzej,

The error message says that custom scale is not correct.

from help:

DAQmxCreateCIAngEncoderChan

int32 DAQmxCreateCIAngEncoderChan (TaskHandle taskHandle, const char counter[], const char nameToAssignToChannel[], int32 decodingType, bool32 ZidxEnable, float64 ZidxVal, int32 ZidxPhase, int32 units, uInt32 pulsesPerRev, float64 initialAngle, const char customScaleName[]);

There are 2 parts where custome scale is taking place - units and customScaleName.

if i compare function declaration with your code:

DAQmxCreateCIAngEncoderChan(taskHandleCont, "Dev1/ctr0", "", DAQmx_Val_EncoderType2_X4, False, 0, DAQmx_Val_EncoderZIndexPhase1_AHighBLow, DAQmx_Val_LengthUnits3_Ticks, 29, 0, ByVal 0&)

then I can think of some mistype. If you are not using custom scale, name must be set to NULL:

customScaleName

const char []

The name of a custom scale to apply to the channel. To use this parameter, you must set units to DAQmx_Val_FromCustomScale. If you do not set units to DAQmx_Val_FromCustomScale, you must set customScaleName to NULL.

another think is parameter units:

units

int32

The units to use to return angular position measurements from the channel. Value   Description DAQmx_Val_Degrees   Degrees DAQmx_Val_Radians   Radians DAQmx_Val_Ticks   Timebase ticks DAQmx_Val_FromCustomScale   Units a custom scale specifies. Use customScaleName to specify a custom scale.

from what i can see in your code, there is DAQmx_Val_LengthUnits3_Ticks, which I don't think is proper value. Remove the 3 from name

I hope I'm not mistaken.

Regards,

Stefo

[AndrzejS]

Hi Stefo,

Thanks for your help, I've put the proper values. The index has been put as an artefact (in true, there are different indexes for linear and angular encoders).
But I still have a problem with reading position from encoder 😞

After creating Counter Input Channels I use code:

    DAQmxErrChk DAQmxStartTask(taskHandleCont)
   
    While taskIsRunningCont = True
        DAQmxErrChk DAQmxReadCounterF64(taskHandleCont, 10000, 10, dataH, 10000, dataL, ByVal 0&)
        countTextBox.Text = Conversion.CStr(dataL)
        DoEvents
    Wend

But it dosen't work.
When I put "" (instead bolded ByVal 0&) at last position in DAQmxReadCounterF64, I obtained error "reserved parameter must be NULL"

And, when I put "ByVal 0&" the program is terminated without any messages 😞

Regards,

Andrzej

[Stefo]

Hi Andrzej,

what programming language do you use? Is it VB, VB .NET or something different?

It is a while since i was using text languages, but as I found out, VB might have issues with ByVal 0&. It depends on how the function is declared. However, according to the NI-DAQmx C API Visual Basic 6.0 Help, you should instead NULL pass 'ByVal 0&' for reserved parameters. So now i'm not sure.

If you use VB 6, you might try to reset your DAQ board (which I'm not sure will help you): Error -200492 "Reserved Parameter Must Be NULL" With Visual Basic 6 and NI-DAQmx

From my view, code seems to be fine, the question is how to pass NULL value properly. The think I can recomend is to open example - this you can install with DAQmx driver, you just need to install it manually (NI-DAQmx Examples for Visual Basic 6.0).

regards,

Stefo