How Many Counters Does Each Type of Counter Task Require

Updated Apr 26, 2018

• 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 Measurement Polymorphic Instance Number of Counters Brief Description CI Freq: Low Frequency with 1 Counter 1 Use one counter that uses a constant timebase to measure the input signal CI Freq: High Frequency 2 Counters 2 Use two counters to count pulses of the signal to measure during measurement time CI Period: Large Range with 2 Counters 2 Use 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 Edges 1 You 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 Width 1 Same as CI Count Edges CI Pulse Measurement (Freq/Time/Ticks) 1 Same as CI Count Edges CI Semiperiod 1 Same as CI Count Edges CI Angular Encoder 1 Same as CI Count Edges CI Linear Encoder 1 Same as CI Count Edges CI Two-Edge Separation 1 Same as CI Count Edges CI GPS Timestamp 1 Same 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 Generated Polymorphic Instance Number of Counters Brief Description Single 1 Pulse 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) 1 Use DAQmx Timing VI to set sampling mode to “Continuous Samples” then use an empty loop to perpetuate pulse generation application Finite 2* 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.