Access Counter with ANSI C

Question

Hi Folks,
I am trying to access counter  using ANSI C (python wrapper actually). Now I am able to read number of counts with sets of commands:
DAQmxCreateTask("", &task);
DAQmxCreateCICountEdges(task, "Dev1/ctr0", "", DAQmx_Val_Rising, 0, DAQmx_Val_CountUp);
DAQmxSetCICountEdgesTerm(task, "Dev/ctr0", "Dev1/PFI11");
DAQmxStartTask(task);
DAQmxReadCounterScalarU32(task, 10, &data, NULL) 
This example cumulates all counts since task was started, so I can get all counts from begining of task or from previous call (using internal software buffer).
But what I want to do is count non-periodical series of 'events'  represented with TTL/NIM pulses. So I want to set up measurement (integration) time for one single shot (let say 1000 ms) and then in loop read number of counts (=events) in this window (i.e. frequency in Hz). I probably need to trigger the 'counting function' in some way, probably something like DAQmxCfgSampClkTiming...
Can you please show me short, simple piece of code, how to do this?
Thanks a lot.
Radek 

Answer 1

Hi Stefo,
Thanks for trying to help me.
I tried to use DAQmxCreateCIPeriodChan and it works fine, but it just not what I was looking for. In our application, we have to read counts from multiple counters (usually 3) in the same time window and the signal is NOT periodic (if it matters). Also it blocks one more counter for each one in the task, so if I need 3 Inputs, the 6601 cards with just 4 counters is not enough. Maybe if it is be possible to share that "gate" counter, I will need just 4 and also it will be maybe possible to count corresponding events in the same time window.
But I found a solution. This "code" (seems to) do exactly what I need:
(this is just important part of Python code, but I guess it is very easy to read, so...)
def cOut0(self, chan, up = 1, down = 0.1, samps = 1e3, num = -1):
    err1 = self.device.DAQmxCreateCOPulseChanTime(self.task, char(chan), char(""), int32(DAQmx_Val_Seconds), int32(DAQmx_Val_Low), float64(0), float64(down), float64(up))
    if num > 0:
        err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_FiniteSamps), uInt64(num))
    else:
        err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_ContSamps), uInt64(samps))
def cOut1(self, chan, freq = 1e3, duty = 0.1, samps = 1e3, num = -1):
    err1 = self.device.DAQmxCreateCOPulseChanFreq(self.task, char(chan), char(""), int32(DAQmx_Val_Hz), int32(DAQmx_Val_Low), float64(0), float64(freq), float64(duty))
    if num > 0:
        err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_FiniteSamps), uInt64(num))
    else:
        err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_ContSamps), uInt64(samps))
def cIn5(self, chan, trig, rate = 1e9, samps = 1e3):
    err1 = self.device.DAQmxCreateCICountEdgesChan(self.task, char(chan), char(""), int32(DAQmx_Val_Rising), uInt32(0), int32(DAQmx_Val_CountUp))
    err2 = self.device.DAQmxSetPauseTrigType(self.task, int32(DAQmx_Val_DigLvl))
    err3 = self.device.DAQmxSetDigLvlPauseTrigSrc(self.task, char(trig))
    err4 = self.device.DAQmxSetDigLvlPauseTrigWhen(self.task, int32(DAQmx_Val_Low))
def wait(self, tOut = -1):
    tOut = float(tOut)
    err = self.device.DAQmxWaitUntilTaskDone(self.task, float64(tOut))
def gCts(self, tout = 1.0, buff = False):
    tout = float(tout)
    ret = numpy.zeros(1, dtype=numpy.uint32)
    err = self.device.DAQmxReadCounterScalarU32(self.task, float64(tout), ret.ctypes.data, bool32(0))
    return ret[0]
And here is terminal output (important part):
>>> devOS.createTask(taskName = "OS")
>>> devOS.cOut1(chan = "/Dev1/ctr0", freq = 1e5)
>>> devOS.startTask()
>>>
>>> devOG = pydaq.nidaq()
>>> devOG.createTask(taskName = "OG")
>>> devOG.cOut0(chan = "/Dev1/ctr1", up = 1, down = 0.1, num = 1)
>>>
>>> devIA = pydaq.nidaq()
>>> devIA.createTask(taskName = "IA")
>>> devIA.cIn5(chan = "/Dev1/ctr2", trig = "/Dev1/PFI32")
>>>
>>> devIB = pydaq.nidaq()
>>> devIB.createTask(taskName = "IB")
>>> devIB.cIn5(chan = "/Dev1/ctr3", trig = "/Dev1/PFI32")
>>>
>>> devIC = pydaq.nidaq()
>>> devIC.createTask(taskName = "IC")
>>> devIC.cIn5(chan = "/Dev1/ctr4", trig = "/Dev1/PFI32")
>>>
>>> import time
>>> def fce(n):
    T1 = time.time()
    r = []
    for i in xrange(n):
        t1 = time.time()
        devIA.startTask(); devIB.startTask(); devIC.startTask();
        devOG.startTask()
        devOG.wait()
        devOG.stopTask()
        c = [devIA.gCts(), devIB.gCts(), devIC.gCts()]
        devIA.stopTask(); devIB.stopTask(); devIC.stopTask();
        t = time.time() - t1
        r.append(c)
        print "%d: %d %d %d (%d s)" % (i + 1, c[0], c[1], c[2], t)
    T = (time.time() - T1) / float(n)
    print "Total Average Time: %d s" % (T)
    return r
>>> a = fce(10)
1: 100000 100000 100000 (1 s)
2: 100000 100000 100000 (1 s)
3: 100000 100000 100000 (1 s)
4: 100000 100000 100000 (1 s)
5: 100000 100000 100000 (1 s)
6: 100000 100000 100000 (1 s)
7: 100000 100000 100000 (1 s)
8: 100000 100000 100000 (1 s)
9: 100000 100000 100000 (1 s)
10: 100000 100000 100000 (1 s)
Total Average Time: 1 s
So conclusion:
1) I know I can put all Input Tasks together to only one task, but when I try to read the counts with DAQmxReadCounterU32 function, I get error -200523. So what Read function is for task with multiple counters?
2) All those Trigger functions I used I found somewhere on the internet. Where is documentation? I can not find it in NI-DAQmx C Reference Help. Also in the header file, there are a lot of functions prototypes of which are not mentioned in the documentation.
3) When I change the lowTime parameter in function DAQmxCreateCOPulseChanTime, the time of measurement does not change, so it seems that this part of pulse is not part of 'task' and/or the DAQmxWaitUntilTaskDone function waits just when the trigger pulse is high. This decreases our death time, because it seems not be possible to set duty cycle to 100 %, but still it is little confusing for me.
Diky moc
Radek
P.S.: Ten "editor" na vlkadani dotazu je udesnej... :-)