NI-9218 Getting Started

Connector Types

The NI-9218 has more than one connector type: NI-9218 with LEMO and NI-9218 with DSUB. Unless the connector type is specified, NI-9218 refers to both connector types.

NI-9218 Pinout


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Table 1. Signals by Measurement Type
Mode Pin
1 2 3 4 5 6 7 8 9 10 [1]1 NI-9218 with LEMO only.
±16 V EX+ AI-, EX- AI+
±65 mV EX+ 2 Optional sensor excitation. [2] EX- [2] AI+ AI- [3]3 Tie to pin 3.
Full-Bridge EX+ [2] EX- [2] RS+ RS- AI+ AI- SC SC
IEPE AI+ AI-
TEDS T+ [4]4 TEDS Class 1 data connection. T- T+ [5]5 TEDS Class 2 data connection.
Table 2. Signal Descriptions
Signal Description
AI+ Positive analog input signal connection
AI- Negative analog input signal connection
EX+ Positive sensor excitation connection
EX- Negative sensor excitation connection
RS+ Positive remote sensing connection
RS- Negative remote sensing connection
SC Shunt calibration connection
T+ TEDS data connection
T- TEDS return connection

Measurement Types

The NI-9218 provides built-in support for the following measurement types.

  • ±16 V
  • ±65 mV
  • Full-Bridge
  • IEPE
Tip NI-recommends using the NI-9982 screw-terminal adapter when using built-in measurement types on the NI-9218.

The NI-9218 provides additional support for the following measurement types when using a measurement-specific adapter.

  • ±20 mA, requires the NI-9983
  • ±60 V, requires the NI-9987
  • Half-Bridge, requires the NI-9986
  • Quarter-Bridge, requires the NI-9984 (120 Ω) or NI-9985 (350 Ω)

±16 V Connections


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The NI-9218 provides optional 12 V sensor excitation. To use the 12 V excitation, connect a 9 VDC to 30 VDC power supply to Vsup, connect the excitation terminals on your sensor to EX+/EX-, and enable 12 V excitation in your software.

±65 mV Connections


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  • You must connect AI- to EX- on the NI-9218.
  • The NI-9218 provides optional 12 V sensor excitation. To use the 12 V excitation, connect a 9 VDC to 30 VDC power supply to Vsup, connect the excitation terminals on your sensor to EX+/EX-, and enable 12 V excitation in your software.

Full-Bridge Connections


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  • The NI-9218 provides 2 V excitation to loads ≥120 Ω or 3.3 V excitation to loads ≥350 Ω.
  • The NI-9218 provides optional connections for remote sensing (RS) and shunt calibration (SC). Remote sensing corrects for errors in excitation leads and shunt calibration corrects for errors caused by resistance within one leg of the bridge.

IEPE Connections


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  • The NI-9218 provides an excitation current for each channel that powers IEPE sensors.
  • AI+ provides DC excitation and AI- provides the excitation return path.

±20 mA Connections


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  • Connecting ±20 mA signals requires the NI-9983.
  • The NI-9218 provides optional 12 V sensor excitation. To use the 12 V excitation, connect a 9 VDC to 30 VDC power supply to Vsup, connect the excitation terminals on your sensor to EX+/EX-, and enable 12 V excitation in your software.

Connecting a loop-powered 2-wire or 3-wire transducer requires adding a 20 kΩ resistor between AI- and Ex-.


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±60 V Connections


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Connecting ±60 V signals requires the NI-9987.

Half-Bridge Connections


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  • Connecting half bridges requires the NI-9986.
  • The NI-9218 provides 2 V excitation to half bridges of ≥240 Ω total or 3.3 V excitation to half bridges of ≥700 Ω total.
  • The NI-9218 provides optional connections for remote sensing (RS) and shunt calibration (SC). Remote sensing corrects for errors in excitation leads and shunt calibration corrects for errors caused by resistance within one leg of the bridge.

Quarter-Bridge Connections


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  • Connecting 120 Ω quarter bridges requires the NI-9984.
  • Connecting 350 Ω quarter bridges requires the NI-9985.
Tip NI-recommends 2 V excitation when using a NI-9984 with 120 Ω quarter bridges and 3.3 V excitation when using the NI-9985 with 350 Ω quarter bridges.

TEDS Connections


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For more information about TEDS, visit ni.com/info and enter the Info Code rdteds.

TEDS Support

TEDS Class 1 sensors provide an interface for transferring information from sensors. The NI-9218 with LEMO, NI-9218 with DSUB, NI-9982L, NI-9982D, NI-9982F support TEDS Class 1 sensors.

TEDS Class 2 sensors provide an interface for transferring information from TEDS enabled sensors. The NI-9218 with LEMO, NI-9982L, NI-9983L, NI-9984L, NI-9985L, and NI-9986L support TEDS Class 2 sensors.

Vsup Daisy Chain Topology


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The NI-9218 with LEMO provides four pins on the Vsup connector for daisy chaining.

NI-9218 Connection Guidelines

Make sure that devices you connect to the NI-9218 are compatible with the module specifications.

Custom Cabling Guidelines

Observe the following guidelines when using the NI-9988 solder cup connector adapter or the LEMO crimp connector (784162-01) to create custom cables.

  • Use a shielded cable for all signals.
  • Connect the cable shield to earth ground.
  • Use twisted-pair wiring for the AI+/AI- and RS+/RS- signals to achieve specified EMC performance.

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NI-9218 Block Diagram


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  • Two 24-bit analog-to-digital converters (ADCs) simultaneously sample both AI channels.
  • The NI-9218 provides channel-to-channel isolation.
  • The NI-9218 reconfigures the signal conditioning for each measurement type.
  • The NI-9218 provides excitation for IEPE and bridge completion measurement types.
  • The NI-9218 can provide optional 12 V sensor excitation for ±16 V, ±65 mV, and ±20 mA measurement types.

±16 V and ±65 mV Signal Conditioning


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Input signals on each channel are buffered, conditioned, and then sampled by an ADC.

Full-Bridge Signal Conditioning


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  • The analog input connections sense then amplify the incoming analog signal.
  • The excitation connections provide differential bridge-excitation voltage.
  • Remote sensing continuously and automatically corrects for lead-wire induced excitation voltage loss when using the RS connections.
  • Shunt calibration can be used to correct for lead-wire induced desensitization of the bridge.

IEPE Signal Conditioning


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  • The incoming analog signal is referenced to an isolated ground.
  • Each channel is configured for AC coupling with an IEPE current.
  • Each channel provides a TEDS Class 1 interface.

±20 mA Signal Conditioning


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The NI-9983 provides a current shunt for the incoming analog signal.

±60 V Signal Conditioning


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The NI-9987 provides an attenuator for the incoming analog signal.

Half-Bridge Signal Conditioning


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  • The NI-9886 provides half bridge completion resistors for the incoming analog signal.
  • You must connect AI+, EX+, and EX-.
  • RS+ and RS- connections are optional.
  • You do not need to connect the AI- signal because it is connected internally.

Quarter-Bridge Mode Conditioning


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The NI-9984 and NI-9985 provide a quarter-bridge completion resistor and half-bridge completion resistors.

Filtering

The NI-9218 uses a combination of analog and digital filtering to provide an accurate representation of in-band signals while rejecting 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 alias-free bandwidth.

The NI-9218 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-9218 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.

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 signal that appears in the alias-free bandwidth of the NI-9218 is not an aliased artifact 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, and it is equal to the data rate minus the stopband frequency.

Opening a Measurement Adapter

What to Do


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  1. Unlock the measurement adapter housing/cover.
  2. Slide the measurement adapter housing/cover to access the screw terminals.

Mounting the NI-998xD/998xL

What to Use

  • NI-998xD or NI-998xL Measurement Adapter
  • M4 or Number 8 Screw
  • Screwdriver

What to Do


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Mount the measurement adapter to a flat surface using the mounting hole on the measurement adapter and the screw.

Measurement Adapter Grounding

The ground terminals on a measurement adapter are connected to chassis ground when the measurement adapter is connected to the NI-9218 and the NI-9218 is installed in a chassis.

Measurement Adapter Pinouts

The following sections include pinouts for the NI-9218 measurement adapters.

NI-9982 ±16 V Connection Pinout


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Pins 3a and 3b are tied together on the NI-9982.

NI-9982 ±65 mV Connection Pinout


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Pins 3a and 3b are tied together on the NI-9982.

NI-9982 Full-Bridge Connection Pinout


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Pins 3a and 3b are tied together on the NI-9982.

NI-9982 IEPE Connection Pinout


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Pins 3a and 3b are tied together on the NI-9982.

NI-9983 Pinout


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Pins 3a and 3b are tied together on the NI-9983.

NI-9987 Pinout


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Pins 3a and 3b are tied together on the NI-9987.

1 NI-9218 with LEMO only.

2 Optional sensor excitation.

3 Tie to pin 3.

4 TEDS Class 1 data connection.

5 TEDS Class 2 data connection.