USB-6211 - Getting Error 50103 when attempting to use two counter method

Question

I am using a USB-6211 and want to measure the speed of a motor by counting pulses coming back from sensors on the motor. Speed will vary from 0 to about 5k Hz.
My strategy is to use "Method 2" in the manual to measure using two counters.  To do this I am attempting to generate pulses of known duration with Counter 0, route these pulses to the gate of Counter 1, send the motor pulses into the source of the counter1 and letting the counter determine and report the number of pulses that occur during the "gate time".
To get the pulse generator going at 8,333 Hz I do this:
AGniDAQmx_CreateTask(instrHandle,"TimingPulses, Task_Handle8)
AGniDAQmx_CreateCOPulseChanFreq(instrHandle, Task_Handle8,"Dev1/Ctr0","Out",DAQmx_Val_Hz,0,8.333,0.5)
AGniDAQmx_CfgImplicitTiming(instHandle, Task_Handle8, DAQmx_ValContStamps,1000)
AGniDAQmx_StartTask(instrHandle, Task_Handle8)
This works fine.  (By the way, I do stop and clear the task before exiting.)
Now I add this code in a new task to try to use the Counter0 pulses to measure the input pulses with Counter1.
AGniDAQmx_CreateTask(instrHandle,"MotorPulses, Task_Handle5)
AGniDAQmx_CreateCIFreqChan(instrHandle,Task_Handle5,"Dev/ctr1",MotorPulses,0,10k,DAQmx_Val_Hz,DAQmx_Val_Rising,DAQmx_ValHighFreq2Ctr,0.12,10,"")
AGniDAQmx_ReadCounterScalarU32(instrHandle,Task_Handle5,10,E)
AGniDAQmx_ClearTask(instrHandle,Task_Handle5)
This function fails on the CreateCIFreqChan() call with an DAQMXError 50103.
Apparently Counter1 resources are being tied up by Counter0.  Is this true?
Any suggestions?
Thanks,
-CBJohnson

Answer 1

Hi Mallori,
Thanks for the great reply message.  I do appreciate your help.
Yes, I think you understand my application.  The motor can turn from zero to about 5K RPM and one pulse is generated with each turn of the motor.
This application is using Agilent VEE but the statements are "C-like" so that's why I posted them like that.  I can't "cut-and-paste" directly from the VEE statements and I have to type them.  I mis-typed the Implicit Timing statement.  It was missing an "_".  It should have been:
AGniDAQmx_CfgImplicitTiming(instrHandle,Task_Handle8,DAQmx_Val_ContStamps,1000)
I think I understand what you are saying about DAQmx_Val_HighFreq2Ctr using the resources from both counters  That explains why I get the message about resources not being available.  
I have tried to use Counter Method 1 and it *almost* worked.  A problem comes about when the motor speed is zero (stopped) and, since these motor pulses are being fed into the Gate of the counter, the zero value makes it simply time out.  Increasing the timeout value to infinite (-1) makes the entire program hang.  I need it to go on -- looking for other user input, reporting other data being collected, etc. If the counter is waiting for the Gate signal to rise to start counting and to drop to stop counting and do the calculation, it will not work since it just times out.  I went to this counter method (actually called counter method 3 in the DAQ manual) because then I am trying to generate the pulses of known period and send these pulses to the Gate.  Then I am feeding my pulses into the Source of the counter and letting it determine how many pulses occured during the "gate time".  In this case, zero pulses during the "gate time" should be OK; it should simply report that zero pulses were detected and start counting again on the next rise of the Gate pulse.  I thought I could simpy adjust the length the "gate time" to measure my range of frequencies.
Make sense?  Any way to do this with the two counters of the USB-6211?
Thanks, Mallori,
-Craig