NI-9244 Getting Started

NI-9244 Block Diagram


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  • Each channel on the NI-9244 provides an independent signal path and ADC. Each terminal has the same input impedance to ground.
  • The NI-9244 returns the voltage between each AI terminal and the Neutral terminal as well as the voltage between the Neutral terminal and the chassis ground.

Filtering

The NI-9244 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-9244 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

The signals within the passband have frequency-dependent gain or attenuation. The small amount of variation in gain with respect to frequency is called the passband flatness. The digital filters of the NI-9244 adjust the frequency range of the passband to match the data rate. Therefore, the amount of gain or attenuation at a given frequency depends on the data rate.

Figure 1. Typical Passband Response for the NI-9244

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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-9244. The NI-9244 includes an internal master timebase with a frequency of 12.8 MHz, but the module also can accept an external master timebase or export its own master timebase. To synchronize the data rate of an NI-9244 with other modules that use master timebases to control sampling, all of the modules must share a single master timebase source.

The following equation provides the available data rates of the NI-9244:

fs=fM÷256n

where n is any integer from 1 to 31.

However, the data rate must remain within the appropriate data rate range. When using the internal master timebase of 12.8 MHz, the result is data rates of 50 kS/s, 25 kS/s, 16.667 kS/s, and so on down to 1.613 kS/s depending on the value of n. When using an external timebase with a frequency other than 12.8 MHz, the NI-9244 has a different set of data rates.

Note The NI-9151 R Series Expansion chassis does not support sharing timebases between modules.

NI-9244 Pinout


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Table 1. Signal Descriptions
Signal Description
AI Analog input signal connection referenced to the Neutral signal
Neutral Referenced, single-ended analog input connection

Connecting Phase Measurements

The NI-9244 accepts three-phase and single-phase measurement configuration.

Three-Phase Measurement Configurations

NI recommends the following three-phase connection types.

4-Wire WYE Measurement Configuration


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High-Leg Delta Measurement Configuration


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3-Wire Delta Measurement Configuration


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Corner Grounded 2-Wire Delta Measurement Configuration


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The 9244 cannot measure the entire tolerance range or high crest factor signals on 690 Vrms systems in this configuration.

Connecting Single-Phase Measurement Configurations

NI recommends the following single-phase connection types.

3-Wire Measurement (Split Phase) Configuration


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2-Wire Measurement


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Connection Guidelines

  • You must use 2-wire ferrules to create a secure connection when connecting more than one wire to a single terminal on the NI-9244.
  • Make sure that devices you connect to the NI-9244 are compatible with the module specifications.

To ensure that measurements to chassis ground are correct, NI recommends connecting the chassis to earth ground using the chassis grounding screw. Refer to your chassis manual for information about connecting the chassis to earth ground.

High-Vibration Application Connections

If your application is subject to high vibration, NI recommends that you follow these guidelines to protect connections to the NI-9244:

  • Use ferrules to terminate wires to the detachable connector.
  • Use the NI-9969 connector backshell kit.

Wiring the NI-9969

Caution For safe operation with hazardous voltages, you must use the NI-9969 Connector Backshell with the 4-terminal connector on the NI-9244.
Attention Pour un fonctionnement en toute sécurité avec des tensions dangereuses, vous devez utiliser le capot de protection de connecteurs NI-9969 avec le connecteur à 4 bornes sur le NI-9244.

Complete the appropriate procedure for each wire gauge.

Installing the NI-9969 Using 12 AWG to 14 AWG Wire

What to Use
  • NI-9969 backshell
  • 12 AWG to 14 AWG wire
  • Smallest strain-relief piece
  • Screwdriver
What to Do

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  1. Route wires under the smallest strain-relief piece.
  2. Secure the smallest strain-relief piece and the backshell in place using captive screws.

Installing the NI-9969 Using 16 AWG Wire

What to Use
  • NI-9969 backshell
  • 16 AWG wire
  • Small and large strain-relief pieces
  • Screwdriver
What to Do

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  1. Route wires between the two strain-relief pieces, with the small strain-relief piece on top of the wires and the large strain-relief piece underneath the wires.
  2. Secure the strain-relief pieces and the backshell in place using captive screws.

Installing the NI-9969 Using 18 AWG to 24 AWG Wire

What to Use
  • NI-9969 backshell
  • 18 AWG to 24 AWG wire
  • Largest strain-relief piece
  • Screwdriver
What to Do

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  1. Route wires under the largest strain-relief piece.
  2. Secure the largest strain-relief piece and the backshell in place using captive screws.

Converting L-N Measurements to L-Earth

To convert L-N measurements to L-Earth values, add the neutral channel reading to each AI channel reading.

Refer to the following equation for an example of converting L-N measurements to L-Earth.

Line to Earth = AIx + Neutral

where

  • AIx is the analog input channel reading
  • Neutral is the Neutral channel reading

Converting L-N Measurements to L-L

To convert L-N measurements to L-L values, calculate the voltage difference between the AI channels using your application software.

Refer to the following equation for an example of converting L-N measurements to L-L.

Phase A to Phase B Voltage = AI0 - AI1

where

  • AI0 is the reading from Phase A
  • AI1 is the reading from Phase B