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DAQmx Create Virtual Channel (Counter Input » Period) (G Dataflow)

Last Modified: September 18, 2017

Creates a channel to measure the period of a digital signal. With the exception of devices that support multi-counter tasks, you can create only one counter input channel at a time with this node, because a task can contain only one counter input channel. To read from multiple counters simultaneously, use a separate task for each counter. Connect the input signal to the default input terminal of the counter, unless you select a different input terminal.

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task in

task in specifies the task to which to add the virtual channels this node creates. If you do not specify a task, NI-DAQmx creates a task for you, and adds the virtual channels this node creates to that task.

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counter

counter specifies the name of the counter to use to create the virtual channel. The DAQmx physical channel constant lists all physical channels, including counters, for devices installed in the system.

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name to assign

name to assign specifies a name to assign to the virtual channel this node creates. If you do not wire a value to this input, NI-DAQmx uses the physical channel name as the virtual channel name.

If you use this input to provide your own names for the virtual channels, you must use the names when you refer to these channels in other NI-DAQmx nodes, such as the source input of the DAQmx Trigger node.

If you create multiple virtual channels with one DAQmx Create Virtual Channel node, you can specify a comma-separated list of names to assign to the virtual channels. If you provide fewer names than the number of virtual channels you create, NI-DAQmx automatically assigns names to the virtual channels.

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units

units specifies the units to use to return time or period measurements.

Name Description
From Custom Scale

Units a custom scale specifies. If you select this value, you must wire a custom scale name to the custom scale name input.

Seconds

Seconds.

Ticks

Timebase ticks.

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error in

error in describes error conditions that occur before this node runs. This input provides standard 'error in' functionality.

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measurement range

measurement range specifies the minimum and maximum values you expect to measure.

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maximum value

maximum value specifies in units the maximum value you expect to measure.

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minimum value

minimum value specifies in units the minimum value you expect to measure.

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measurement method

measurement method specifies the method to use to calculate the period or frequency of the signal.

Name Description
High Frequency with 2 Counters

Use two counters to count pulses of the signal to measure during measurement time.

Large Range with 2 Counters

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.

Low Frequency with 1 Counter

Use one counter that uses a constant timebase to measure the input signal.

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custom scale name

custom scale name specifies the name of a custom scale for the channel.

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starting edge

starting edge specifies between which edges to measure the frequency or period of the signal.

Name Description
Falling

Measure between falling edges.

Rising

Measure between rising edges.

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measurement time

measurement time is the length of time in seconds to measure the frequency or period of the signal, if measurement method is High Frequency with 2 Counters. Leave this input unwired, if measurement method is not High Frequency with 2 Counters.

Measurement accuracy increases with increased measurement time and with increased signal frequency. If you measure a high-frequency signal for too long, however, the count register could roll over, which results in an incorrect measurement.

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divisor

divisor is the value by which to divide the input signal when measurement method is Large Range with 2 Counters. Leave this input unwired, if measurement method is not Large Range with 2 Counters.

The larger the divisor, the more accurate the measurement. However, too large a value could cause the count register to roll over, which results in an incorrect measurement.

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task out

task out is a reference to the task after this node runs. The task contains any newly created virtual channels. If you did not wire a value to task in, NI-DAQmx automatically creates the task this output refers to.

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error out

error out contains error information. If error in indicates that an error occurred before this node ran, error out contains the same error information. Otherwise, error out describes the error status that this node produces.

Where This Node Can Run:

Desktop OS: Windows

FPGA: LabVIEW NXG does not support FPGA devices

Web Server: Not supported in VIs that run in a web application


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