NI-9239 Getting Started

In this document, the NI-9239 with screw terminal and NI-9239 with BNC are referred to inclusively as the NI-9239. The information in this document applies to all versions of the NI-9239 unless otherwise specified.

NI-9239 Pinout


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Table 1. Signal Descriptions
Signal Description
AI+ Positive analog input signal connection
AI- Negative analog input signal connection

Cable Requirements

Select and install cables for the NI-9239 with BNC in accordance with the following EMC requirements:

  • Install a clamp-on ferrite bead (NI part number 782801-01) on the BNC cable for each channel that you are connecting to on the NI-9239 with BNC.
  • Clamp-on ferrites must be connected to the BNC cable as close to the module as possible with a full turn as shown in the following figure. Placing the ferrite elsewhere on the cable noticeably impairs its effectiveness.
Figure 1. Installing a Ferrite

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Grounded Connections


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Make sure the voltage on the AI+ and AI- connections are in the channel-to-earth safety voltage range to ensure proper operation.

Floating Connections


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NI-9239 Connection Guidelines

  • Make sure that devices you connect to the NI-9239 are compatible with the module specifications.
  • You must use 2-wire ferrules to create a secure connection when connecting more than one wire to a single terminal on the NI-9239 with screw terminal.

Wiring for High-Vibration Applications

If your application is subject to high vibration, NI recommends that you follow these guidelines to protect connections to the NI-9239 with screw terminal:
  • Use ferrules to terminate wires to the detachable connector.
  • Use the NI-9971 backshell kit.

NI-9239 Block Diagram


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  • Input signals on each channel are conditioned, buffered, and then sampled by an ADC.
  • Each AI channel provides an independent signal path and ADC, enabling you to sample all channels simultaneously.

Filtering

The NI-9239 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-9239 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-9239 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 2. Typical Passband Response for the NI-9239

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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-9239. The NI-9239 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-9239 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-9239:

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-9239 has a different set of data rates.

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

Conformal Coating

The NI-9239 is available with conformal coating for additional protection in corrosive and condensing environments, including environments with molds and dust.

In addition to the environmental specifications listed in the NI-9239 Safety, Environmental, and Regulatory Information, the NI-9239 with conformal coating meets the following specification for the device temperature range. To meet this specification, you must follow the appropriate setup requirements for condensing environments. Refer to Conformal Coating and NI RIO Products for more information about conformal coating and the setup requirements for condensing environments.

Operating humidity (IEC 60068-2-30 Test Db) 80 to 100% RH, condensing