How Many Counters Does Each Type of Counter Task Require - National Instruments

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How Many Counters Does Each Type of Counter Task Require

Updated Apr 26, 2018

Reported In

Reported In shows products that are verified to work for the solution described in this article. This solution might also apply to other similar products or applications.

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 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.

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.