Hi everyone,
I am currently running into a problem I cant seam to fix.
To measure a linear position I use an encoder task. The task itselfe works well and counts the position as planned.
Still I am running into a major issue: For a new measurement I need to clear the buffer of the encoder task, because I dont want to get any old data. As just reading all the data out of the buffer (_encoderTask.Stream.ReadAllAvailableSamples = true; + _encoderTaskReader.ReadMultiSampleInt32(-1); )d oesnt do the job, there are still samples in the buffer.
So i followed this guide and tried to delete the task and create a new one for the new measurement. Now the problem is: if I read the current position from the encoder task, delete the task and create a new task with its startingposition to be the same as the last position of the old task, the positions dont match. I make an example to make this clear:
The task was running. Now I read the current position:
// Clear Buffer
_encoderTaskReader.ReadMultiSampleInt32(-1);
// We need to start the clock task to get at least one sample
_clockTask.Start();
UInt32 pos = _encoderTaskReader.ReadSingleSampleUInt32();
_clockTask.Stop();
// Clear Buffer
_encoderTaskReader.ReadMultiSampleInt32(-1);
I need to start the clock task for a very short amount of time, so a new sample is generated and I can read the current position.
Now that I have the current position (in Ticks) I reinit the encoder task:
_encoderTask.CIChannels.CreateLinearEncoderChannel(DeviceName + "/ctr0", "Encoder 1", CIEncoderDecodingType.X4, false, 0, CIEncoderZIndexPhase.AHighBHigh, 1, (double)pos/ 4, CILinearEncoderUnits.Ticks);
Funny thing here is: the read position gives you the position in ticks, but you need to devide this number by 4 to set the starting position, cause he doesn't accept the position in ticks but in "samples".
If i now read the position again:
// Clear Buffer
_encoderTaskReader.ReadMultiSampleInt32(-1);
// We need to start the clock task to get at least one sample
_clockTask.Start();
UInt32 pos2 = _encoderTaskReader.ReadSingleSampleUInt32();
_clockTask.Stop();
// Clear Buffer
_encoderTaskReader.ReadMultiSampleInt32(-1);
pos and pos2 are not the same. The axis was not moving while this happens so there where no ticks generated (checked it with an osciliscope). The position is always 1-5 ticks smaller than the original one. As I generate new tasks every 5 seconds and have alot of measurements (several hundred), this errors sums up really quickly and ruins my measurements.
How do i fix this problem? Is there any way to reset the buffer of the task in another way? How do I initialize the task so the psotion doesn't differ?
Best,
nano
