Configuring the Minimum Time Between Conversions for the NI 9201/9221 (FPGA Interface)

NI CompactRIO Device Drivers Help

Edition Date: December 2017

Part Number: 373197L-01

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You can configure the minimum time between conversions for the NI 9201/9221 in the C Series Module Properties dialog box.

Complete the following steps to configure the minimum time between conversions for the NI 9201/9221.

  1. Configure the CompactRIO system, and add an NI 9201/9221.
  2. Right-click the NI 9201/9221 in the Project Explorer window and select Properties from the shortcut menu to display the C Series Module Properties dialog box.
  3. Enter a value between 0 and 10 µs in increments of 25 ns in the Minimum Time Between Conversions text box.
  4. Click the OK button.
  5. Select File»Save All in the Project Explorer window.
Note Note  The default minimum time between conversions for the NI 9201 is 2 µs, and the default minimum time between conversions for the NI 9221 is 1.25 µs. The accuracy specifications in the NI 9201 and NI 9221 hardware documentation on ni.com/manuals are based on these default values. Refer to the following tables for examples of how the value you enter in the Minimum Time Between Conversions text box affects the actual time between conversions and the accuracy of the module.

Refer to the following table if you are using a chassis other than the NI 9151 R Series Expansion chassis.

ModuleSampling Data
from a Single
or Multiple Channels?
Minimum Time
Between Conversions*
Able to Achieve
Specified Time
Between Conversions?**
Module Accuracy
NI 9201
Single
≥ 1.25 µs
Yes
Module accuracy not affected
< 1.25 µs
No
Module accuracy not affected
Multiple
≥ 2 µs
Yes
Module accuracy not affected
< 2 µs
No
Module accuracy degrades
NI 9221
Single
≥ 1.25 µs
Yes
Module accuracy not affected
< 1.25 µs
No
Module accuracy not affected
Multiple
≥ 1.25 µs
Yes
Module accuracy not affected
< 1.25 µs
No
Module accuracy degrades

Refer to the following table if you are using the NI 9151 R Series Expansion chassis.

ModuleSampling Data
from a Single
or Multiple Channels?
Minimum Time
Between Conversions*
Able to Achieve
Specified Time
Between Conversions?**
Module Accuracy
NI 9201
Single
≥ 2.1 µs
Yes
Module accuracy not affected
< 2.1 µs
No
Module accuracy not affected
Multiple
≥ 2.1 µs
Yes
Module accuracy not affected
< 2.1 µs and ≥ 2 µs
No
Module accuracy not affected
< 2 µs
No
Module accuracy degrades
NI 9221
Single
≥ 2.1 µs
Yes
Module accuracy not affected
< 2.1 µs
No
Module accuracy not affected
Multiple
≥ 2.1 µs
Yes
Module accuracy not affected
< 2.1 µs and ≥ 1.25 µs
No
Module accuracy not affected
< 1.25 µs
No
Module accuracy degrades

* The value you set in the C Series Module Properties dialog box.

** The actual time between conversions depends on how you develop the FPGA VI. Yes indicates that it is possible to write an FPGA VI that can sustain the minimum time between conversions specified in the C Series Module Properties dialog box. No indicates that the minimum time between conversions specified in the C Series Module Properties dialog box is too low and you may not be able to write an FPGA VI that can sustain the specified time.

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