Calculate the Input Delay on NI-9237

Updated Nov 7, 2018

Reported In

Hardware

  • NI-9237
  • NI-9235
  • NI-9236
  • C Series Strain/Bridge Input Device

Issue Details

How do I calculate the input delay on the NI-9237?

Solution

The input delay of C Series Strain/Bridge Input Module, such as NI 9235/9236/9237, can be calculated from the Data Rate (fs).

The Data Rate is the rate at which you collect data. When you see the specification of NI 9237, you can find the below equation.
 
Data Rate (fs) = (fM÷256)÷n, where n is any integer from 1 to 31.
 
And then, This Data Rate is used in the below equation.
 
Input delay = (40 + 5/512)÷ƒs + 4.5 µs.


For Example,

Master Timebase (fM): 12.8 Mhz (Internal)
Integer: 25
      
  • Data Rate (fs) = (fM÷256)/25
Data Rate (fs) = 2 kS/s
 
  • Input delay = (40 + 5/512)÷ƒs + 4.5 µs.
Input delay = 0.0200094 s


Note: When programming, you do not specify the integer value for division on the NI 9237, and you will actually specify your Data Rate.  If your Data Rate does not match a Data Rate that is calculated using an integer, it will be coerced up to the next highest Data Rate.
 

Additional Information

The Data Rate is determined from the master timebase which is the basis for all calculations, this can be either an internal or external clock that can vary in range from 3.102976 Mhz to 13.14816 Mhz, with the internal timebase at 12.8 Mhz. The numerator of the equation refers to the removed samples that occur and contribute to the input delay in all C Series Delta Sigma devices. A similar KB has been linked in Valid Sampling Rates for NI 9234 and NI 9237.

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