Hello,
I am attempting to use python (with ctypes) to control my USB-6009. The goal is to write out an analog voltage and then read in the voltage through an analog input with ability to change the number of points averaged and the number of times this is repeated(sweeps) averaging the analog input array. The issue is that as we increase the number of times the voltage ramp is repeated (sweeps) we get a time out error (nidaq call failed with error -200284: 'Some or all of the samples requested have not yet been acquired). This has us confused because the sweeps are in a larger loop and the Daq function should be the same if there are 10 sweeps (works) or 1000 sweeps (crashes). Any insight would be greatly appreciated. I have included the code below for reference.
import ctypes
import numpy
from time import *
from operator import add
nidaq = ctypes.windll.nicaiu # load the DLL
##############################
# Setup some typedefs and constants
# to correspond with values in
# C:\Program Files\National Instruments\NI-DAQ\DAQmx ANSI C Dev\include\NIDAQmx.h
# Scan Settings
aoDevice = "Dev2/ao0"
aiDevice = "Dev2/ai0"
NumAvgPts = 10
NumSweeps = 50
NumSpecPts = 100
filename = '12Feb15_CO2 Test_12.txt'
Readrate = 40000.0
Samplerate = 1000
StartVolt = 0.01
FinalVolt = 1.01
voltInc = (FinalVolt - StartVolt)/NumSpecPts
# the typedefs
int32 = ctypes.c_long
uInt32 = ctypes.c_ulong
uInt64 = ctypes.c_ulonglong
float64 = ctypes.c_double
TaskHandle = uInt32
# the constants
DAQmx_Val_Cfg_Default = int32(-1)
DAQmx_Val_Volts = 10348
DAQmx_Val_Rising = 10280
DAQmx_Val_FiniteSamps = 10178
DAQmx_Val_GroupByChannel = 0
##############################
def CHK_ao( err 😞
"""a simple error checking routine"""
if err < 0:
buf_size = 100
buf = ctypes.create_string_buffer('\000' * buf_size)
nidaq.DAQmxGetErrorString(err,ctypes.byref(buf),buf_size)
raise RuntimeError('nidaq call failed with error %d: %s'%(err,repr(buf.value)))
if err > 0:
buf_size = 100
buf = ctypes.create_string_buffer('\000' * buf_size)
nidaq.DAQmxGetErrorString(err,ctypes.byref(buf),buf_size)
raise RuntimeError('nidaq generated warning %d: %s'%(err,repr(buf.value)))
def CHK_ai(err):
"""a simple error checking routine"""
if err < 0:
buf_size = NumAvgPts*10
buf = ctypes.create_string_buffer('\000' * buf_size)
nidaq.DAQmxGetErrorString(err,ctypes.byref(buf),buf_size)
raise RuntimeError('nidaq call failed with error %d: %s'%(err,repr(buf.value)))
def Analog_Output():
taskHandle = TaskHandle(0)
(nidaq.DAQmxCreateTask("",ctypes.byref(taskHandle )))
(nidaq.DAQmxCreateAOVoltageChan(taskHandle,
aoDevice,
"",
float64(0),
float64(5),
DAQmx_Val_Volts,
None))
'''
(nidaq.DAQmxCfgSampClkTiming(taskHandle,"",float64(Samplerate),
DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,
uInt64(NumAvgPts))); # means we could turn in this to continuously ramping and reading
'''
(nidaq.DAQmxStartTask(taskHandle))
(nidaq.DAQmxWriteAnalogScalarF64(taskHandle, True, float64(10.0), float64(CurrentVolt), None))
nidaq.DAQmxStopTask( taskHandle )
nidaq.DAQmxClearTask( taskHandle )
def Analog_Input():
global average
# initialize variables
taskHandle = TaskHandle(0)
data = numpy.zeros((NumAvgPts,),dtype=numpy.float64)
# now, on with the program
CHK_ai(nidaq.DAQmxCreateTask("",ctypes.byref(taskHandle)))
CHK_ai(nidaq.DAQmxCreateAIVoltageChan(taskHandle,aiDevice,"",
DAQmx_Val_Cfg_Default,
float64(-10.0),float64(10.0),
DAQmx_Val_Volts,None))
CHK_ai(nidaq.DAQmxCfgSampClkTiming(taskHandle,"",float64(Readrate),
DAQmx_Val_Rising,DAQmx_Val_FiniteSamps,
uInt64(NumAvgPts)));
CHK_ai(nidaq.DAQmxStartTask(taskHandle))
read = int32()
CHK_ai(nidaq.DAQmxReadAnalogF64(taskHandle,NumAvgPts,float64(10.0),
DAQmx_Val_GroupByChannel,data.ctypes.data,
NumAvgPts,ctypes.byref(read),None))
#print "Acquired %d points"%(read.value)
if taskHandle.value != 0:
nidaq.DAQmxStopTask(taskHandle)
nidaq.DAQmxClearTask(taskHandle)
average = sum(data)/data.size
Thanks,
Erin
