NI-9250 Getting Started
- Updated2023-02-17
- 5 minute(s) read
NI-9250 Getting Started
NI-9250
Pinout
Signal | Description |
---|---|
AI+ | Positive analog input signal connection |
AI- | Negative analog input signal connection |
NI-9250
Block Diagram
- Input signals on each channel are buffered, conditioned, and then sampled by an ADC.
- Each AI channel provides an independent signal path to the ADC, enabling you to sample all channels simultaneously.
- AI channels are referenced to earth ground through a protected 50 Ω resistor.
- AC/DC coupling is software-selectable.
- For AI channels set to AC coupling, IEPE excitation current is software-selectable.
- The module protects each channel from overvoltages.
Grounded Connections
Floating Connections
NI-9250
Connection Guidelines
- Make sure that devices you connect to the NI-9250 are compatible with the module specifications.
Integrated Electronic Piezoelectric (IEPE) Sensors
The NI-9250 provides an IEPE excitation current for each channel to measure the IEPE sensors. Typical IEPE sensors have a case that is electrically isolated from the IEPE electronics. As a result, connecting the sensor to the NI-9250 results in a floating connection even though the case of the sensor is grounded.
Filtering
The NI-9250 uses a combination of analog and digital filtering to provide an accurate representation of in-band signals and reject out-of-band signals. The filters discriminate between signals based on the frequency range, or bandwidth, of the signal. The three important bandwidths to consider are the passband, the stopband, and the anti-imaging bandwidth.
The NI-9250 represents signals within the passband, as quantified primarily by passband ripple and phase nonlinearity. All signals that appear in the alias-free bandwidth are either unaliased signals or signals that have been filtered by at least the amount of the stopband rejection.
Passband
Stopband
The filter significantly attenuates all signals above the stopband frequency. The primary goal of the filter is to prevent aliasing. Therefore, the stopband frequency scales precisely with the data rate. The stopband rejection is the minimum amount of attenuation applied by the filter to all signals with frequencies within the stopband.
Alias-Free Bandwidth
Any signals that appear in the alias-free bandwidth are not aliased artifacts of signals at a higher frequency. The alias-free bandwidth is defined by the ability of the filter to reject frequencies above the stopband frequency. The alias-free bandwidth is equal to the data rate minus the stopband frequency.
Data Rates
The frequency of a master timebase (fM) controls the data rate (fs) of the NI-9250 . The NI-9250 includes an internal master timebase with a frequency of 13.1072 MHz. Using the internal master timebase of 13.1072 MHz results in data rates of 102.4 kS/s, 51.2 kS/s, 25.6 kS/s, 17.067 kS/s, and so on down to 267 S/s, depending on the decimation rate and the value of the clock divider. However, the data rate must remain within the appropriate data rate range.
The following equation provides the available data rates of the NI-9250 :
There are multiple combinations of clock dividers and decimation rates that yield the same data rate. The software always picks the highest decimation rate for the selected data rate. The following table lists available data rates with the internal master timebase.
f s (kS/s) | Decimation Rate | Clock Divider |
---|---|---|
102.400 | 32 | 1 |
51.200 | 64 | 1 |
34.133 | 32 | 3 |
25.600 | 128 | 1 |
20.480 | 32 | 5 |
17.067 | 64 | 3 |
14.629 | 32 | 7 |
12.800 | 256 | 1 |
11.378 | 32 | 9 |
10.240 | 64 | 5 |
9.309 | 32 | 11 |
8.533 | 128 | 3 |
7.314 | 64 | 7 |
6.400 | 512 | 1 |
5.689 | 64 | 9 |
5.120 | 128 | 5 |
4.655 | 64 | 11 |
4.267 | 256 | 3 |
3.657 | 128 | 7 |
3.200 | 1024 | 1 |
2.844 | 128 | 9 |
2.560 | 256 | 5 |
2.327 | 128 | 11 |
2.133 | 512 | 3 |
1.829 | 256 | 7 |
1.600 | 1024 | 2 |
1.422 | 256 | 9 |
1.280 | 512 | 5 |
1.164 | 256 | 11 |
1.067 | 1024 | 3 |
0.914 | 512 | 7 |
0.800 | 1024 | 4 |
0.711 | 512 | 9 |
0.640 | 1024 | 5 |
0.582 | 512 | 11 |
0.533 | 1024 | 6 |
0.457 | 1024 | 7 |
0.400 | 1024 | 8 |
0.356 | 1024 | 9 |
0.320 | 1024 | 10 |
0.291 | 1024 | 11 |
0.267 | 1024 | 12 |
The NI-9250 also can accept an external master timebase or export its own master timebase. To synchronize the data rate of an NI-9250 with other modules that use master timebases to control sampling, all of the modules must share a single master timebase source. When using an external timebase with a frequency other than 13.1072 MHz, the NI-9250 has a different set of data rates. Refer to the software help for information about configuring the master timebase source for the NI-9250 .