Connecting Signals to the BNC-2090 to Minimize Noise

Updated Apr 2, 2019

Reported In

Hardware

  • BNC-2090A

Issue Details

I am reading a lot of noise on my measurements using my BNC-2090 terminal block. How do I properly configure a bias resistor? More generally, what are the grounding options for the BNC-2090, and how do I configure them?

Solution

The BNC-2090 terminal connector is designed for use with the BNC-2090 and a 50, 68, or 100-pin MIO DAQ board or a 50-pin PC-LPM-16 DAQ board. 

The BNC-2090 can be set in three different modes for application specific measurements, but all channels must be configured for the same mode. These modes are differential, nonreferenced single-ended (NRSE), or referenced single-ended (RSE). This information can be found in Product Manuals: BNC-2090 User Manual . (The BNC-2090A can be configured to read different channels in different modes.)

The BNC-2090's green-and-orange terminal strip provides access to the DIO and counter/timer features on the E Series boards. The terminal strip "GND" does not reference the AIGND on the DAQ card. Instead this GND is tied to the shield of the connector to the DAQ device. An internal jumper determines the resistance between the GND terminal and the shield. The default setting is 100 Ω, but it can be changed to 0 Ω or open by setting a jumper inside the BNC-2090. 


Measurement Mode Configurations:

  • DIFF (Differential) Mode:
    Set all channel switches to DIFF and set the RSE/NRSE switch to NRSE mode.
    Connect your signals to the ACH0 - ACH7 connectors on the terminal block. The DIFF mode switch connects the center pin of ACH0 - ACH7 to channels 0-7, respectively, and the shield of ACH0 - ACH7 to channels 8 - 15, respectively, on the DAQ device. (For reference, the center pins of ACH8 - ACH15 are also connected to channels 8-15 on the DAQ device in DIFF mode. In other words, in DIFF mode ACH8 - ACH15 are connected to the shield of channels ACH0 - ACH7, respectively.)
    The BNC-2090 is designed to allow for various user-implementable signal conditioning options. Solder pads are available for wiring basic high and low-pass filters as well as bias resistors. These are located on the circuit board inside the BNC-2090. See the user manual for instructions on how to build basic signal conditioning circuits for the BNC-2090.
    Using bias resistors with the BNC-2090 will require partial disassembly of the terminal block. It is necessary to manually solder the resistors to the BNC-2090 circuit board. Please refer to Product Manuals: BNC-2090 User Manual for instructions on how to accomplish this. An alternative method for implementing bias resistors is described in the Bias Resistor Help section at the end of this document.
  • NRSE (Nonreferenced Single-Ended) Mode:
    Set all channel switches to SE. Set the RSE/NRSE switch to NRSE mode.
    In NRSE mode, all BNC connector shields are connected to AISENSE. AISENSE is not accessible from the front of the BNC-2090. You must use the pass-through connector to access the AISENSE line. Refer to the Bias Resistor section of this document for details.
  • RSE (Referenced Single-Ended) Mode:
    Set all channel switches to SE. Set the RSE/NRSE switch to RSE mode.
    In RSE mode, all BNC connector shields are connected to AIGND. AIGND is not accessible from the front of the BNC-2090. You must use the pass-through connector to access the AIGND line. Refer to the Bias Resistor Help section of this document below for details.  Using RSE mode may eliminate some noise when using a floating source. Please refer to the user manual or the white paper titled Field Wiring and Noise Considerations for Analog Signals for help choosing the proper grounding method for your signals. 
Bias Resistor 
The following set-up will allow you to configure the BNC-2090 with bias resistors without dismantling or soldering inside the BNC-2090 box.

Connect another terminal block (such as the SCB-68) via the 68-pin pass-through port to gain access to the AIGND and AISENSE lines on the BNC-2090. If using DIFF mode, connect a bias resistor (10 kΩ - 100 kΩ ) from the negative terminal on the BNC-2090 (i.e. ACH8 - ACH15) to AISENSE (NRSE mode) or AIGND (RSE mode) on the SCB-68.

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