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pythonnidaqmx
Chazzo
Chazzo

Reputation: 23

NI 9207 with nidaqmx with Python, how do I configure sample rates and achieve continuous sampling?

I have worked with nidaqmx in the past. I worked with an NI 9229 (using a usb cDAQ-9171 single slot chassis) which is capable of simultaneous sampling. I could set the sample rate and also continuously sample the buffer with my tkinter application.

I am now working with a NI 9207 (using a usb cDAQ-9171 single slot chassis). I now have 16 channels to sample, and I now have a CONVERT CLOCK to work with as well which I have learned is different from the normal clocks that I am used to adjusting the sample rates on. The usual command I use is

self.task.timing.cfg_samp_clk_timing(sampleRate,source = '/'+self.daqName+'/ai/SampleClock', sample_mode=nidaqmx.constants.AcquisitionType.CONTINUOUS,samps_per_chan=self.numberOfSamples)

I get an error as follows:

DaqReadError: Specified route cannot be satisfied, because the hardware does not support it.
Property: DAQmx_SampClk_Src
Property: DAQmx_SampClk_ActiveEdge
Source Device: cDAQ6Mod1
Source Terminal: ai/ConvertClock

Task Name: _unnamedTask<3B>

Status Code: -89136

I have scrounged for examples and referred also the NI-DAQmx Python Documentation

I have had success in using basic task.read() commands but this frankly doesn't offer the flexibility that I need.

TLDR; I don't know how to change the sample rate and to setup continuous acquisition with an NI card that has a CONVERT CLOCK.

Upvotes: 0

Views: 540

Answers (1)

ZY-Ong
ZY-Ong

Reputation: 16

I didn't receive any error on the convert clock when running the following code with NI-9207. Can you post your full code?

import numpy
from datetime import datetime, timedelta

import nidaqmx
from nidaqmx.constants import AcquisitionType
from nidaqmx.stream_readers import AnalogMultiChannelReader

with nidaqmx.Task() as task:
    # Timing Settings
    sample_rate = 10
    dt = 1/sample_rate
    number_of_samples_per_channel = 10

chan = task.ai_channels.add_ai_voltage_chan("Dev1/ai0:3")
channels_name = task.channel_names
number_of_channels = task.number_of_channels
task.timing.cfg_samp_clk_timing(
sample_rate, sample_mode=AcquisitionType.CONTINUOUS)

stream = AnalogMultiChannelReader(task.in_stream)
dataStream = numpy.zeros((number_of_channels, number_of_samples_per_channel), dtype=numpy.float64)
dataPrint = numpy.zeros((number_of_samples_per_channel, number_of_channels), dtype=numpy.float64)

task.start()
# Python does not support t0 from the first sample of waveform, use current start time as t0 instead
t0 = datetime.now()

try:
    print("Press Ctrl+C to stop")
    print(f'Voltage Data:')
    header = 'Time\t\t\t\t'+'\t'.join([x for x in channels_name])
    print(header)
    while True:
        stream.read_many_sample(dataStream, number_of_samples_per_channel)
        dataPrint = numpy.transpose(dataStream)
        
        output = ''
        for i in range(0,dataPrint.shape[0]):
            output += str(t0)+'\t'+'\t\t'.join(['%0.3f' %x for x in dataPrint[i,:]])+'\n'
            t0 += timedelta(seconds=dt)
        print(output)

except KeyboardInterrupt:
    pass

task.stop()

Upvotes: 0

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