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SC-2043-SG high frequency noise problem
Lionel P
Member
06-08-2005 04:32 AM
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Hi, I am experiencing a very persistent noise problem on my strain guage measurements. The SC-2043-SG card has a built-in low pass filter at 1600Hz. A high frequency spectral analysis of the voltage signal directly acquired through a home-made labview VI reveals that the noise frequency is higher than 1.6kHz, more around the 5-7kHz band. The signal is not being averaged but is a raw measurement. The noise amplitude is 10 to 15mV peak-peak. This noise covers most of the signal, making any gauge readings completely inaccurate. Does anyone have any idea why such high frequency noise is being measured even when the SC card is supposed to filter at those frequencies?
We are using a SC-2043-SG connected to a PCI MIO card 6033. All channels are connected to strain guages. When a channel is shorted, noise is still present but smaller. Strangely, shorting other channels than the one being acquired also reduces the noise on the strain gauge signal, and offsets the signal's zero setting. I suspect the problem is related to different ground signals being interconnected. Thanks for any suggestions!
We are using a SC-2043-SG connected to a PCI MIO card 6033. All channels are connected to strain guages. When a channel is shorted, noise is still present but smaller. Strangely, shorting other channels than the one being acquired also reduces the noise on the strain gauge signal, and offsets the signal's zero setting. I suspect the problem is related to different ground signals being interconnected. Thanks for any suggestions!
Kerouac
NI Employee (retired)
06-13-2005 03:50 AM
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Hello,
AISENSE is ground referenced on the SC-2043-SG. In order to avoid a ground loop, which may affect your measurements, all analog input signals MUST be floating. This pin is the reference node for the conditioned strain gauge bridge signals. AISENSE is directly connected to the excitation supply return and is earth-grounded. This makes AISENSE a low impedance reference. Therefore, all signals referenced to it MUST be floating.
Configure any unused channels for full-bridge connections and short their input screw terminals (CHn±) to their excitation return screw terminals (-EXn). If you are using an external excitation voltage, the -EX input signal is connected to DGND on the SC-2043-SG. Because this lowimpedance connection can cause a ground loop, which may affect your measurements, your excitation voltage source MUST be floating. If you are using an external + 5V power supply, the ground input signal is directly connected to DGND on the SC-2043-SG. In order to avoid a ground loop, which may affect your measurements, your +5 V power supply MUST be floating. Remember that your DAQ board must be configured for NRSE operation and all analog inputs are referenced to AISENSE.
Hope this helps.
Matthieu G.
National Instruments
AISENSE is ground referenced on the SC-2043-SG. In order to avoid a ground loop, which may affect your measurements, all analog input signals MUST be floating. This pin is the reference node for the conditioned strain gauge bridge signals. AISENSE is directly connected to the excitation supply return and is earth-grounded. This makes AISENSE a low impedance reference. Therefore, all signals referenced to it MUST be floating.
Configure any unused channels for full-bridge connections and short their input screw terminals (CHn±) to their excitation return screw terminals (-EXn). If you are using an external excitation voltage, the -EX input signal is connected to DGND on the SC-2043-SG. Because this lowimpedance connection can cause a ground loop, which may affect your measurements, your excitation voltage source MUST be floating. If you are using an external + 5V power supply, the ground input signal is directly connected to DGND on the SC-2043-SG. In order to avoid a ground loop, which may affect your measurements, your +5 V power supply MUST be floating. Remember that your DAQ board must be configured for NRSE operation and all analog inputs are referenced to AISENSE.
Hope this helps.
Matthieu G.
National Instruments
