How Many Counters Does Each Type of Counter Task Require

Updated Apr 26, 2018

Reported In

Driver

  • NI-DAQmx

Issue Details

I am trying to use a DAQmx Create Channel VI for a counter. How many counters are needed for my counter task?

Solution

The following table shows the number of counters required for each of the counter input and output tasks. For some measurements, the number of counters depends on another setting. In these cases, all the possible settings that affect the number of counters have also been included.

Note: These tables specifically cover the number of counters that are used with E and M series DAQ cards. X series devices can perform several of the tasks that required two counters on M and E series devices with only one counter. Such instances are noted in the notes of the table. For more information about counter tasks on X series devices, see Chapter 7 of the X Series User Manual.

Counter Input
Counter MeasurementPolymorphic InstanceNumber of CountersBrief Description
CI Freq: Low Frequency with 1 Counter1Use one counter that uses a constant timebase to measure the input signal
CI Freq: High Frequency 2 Counters2Use two counters to count pulses of the signal to measure during measurement time
CI Period: Large Range with 2 Counters2Use one counter to divide the frequency of the input signal by divisor to create a lower-frequency signal that the second counter can more easily measure
CI Count Edges1You can create only one counter input channel at a time with this VI because a task can contain only one counter input channel. To read from multiple counters simultaneously, use a separate task for each counter
CI Pulse Width1Same as CI Count Edges
CI Pulse Measurement (Freq/Time/Ticks)1Same as CI Count Edges
CI Semiperiod1Same as CI Count Edges
CI Angular Encoder1Same as CI Count Edges
CI Linear Encoder1Same as CI Count Edges
CI Two-Edge Separation1Same as CI Count Edges
CI GPS Timestamp1Same as CI Count Edges

Counter Output
There are three different counter pulse output task types, CO Pulse Freq, CO Pulse Time, CO Pulse Ticks. You specify the number of pulses to generate with the DAQmx Timing VI. Finite pulse generation requires two counters because one counter gates the other to produce the finite pulse train.
 
Number of Pulses GeneratedPolymorphic InstanceNumber of CountersBrief Description
Single1Pulse Generation operates on the principle of a counter’s Terminal Count. When “any” counter register hits the terminal count the output toggles or pulses. Output pulse is equal to one source cycle
Continuous (Infinite until the end of the task)1Use DAQmx Timing VI to set sampling mode to “Continuous Samples” then use an empty loop to perpetuate pulse generation application
Finite2*The first counter generates a pulse of desired width.  The second counter generates the pulse train which is gated by the pulse of the first counter
*Can be performed with only one counter on X series devices and cDAQ chassis with STC3 technology.

Note: Single or finite pulse generation can be retriggerable and do not change the number of counters used.
 

Additional Information

Keep in mind that the maximum a chassis or individual card can hold is 4 counters for the cDAQ line. To add more counters, you would need a specific counter card such as the NI-9361.

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