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Using the SC-2043-SG With the DAQCard-1200

Hardware: Signal Conditioning Other>>SC Analog Accessories

Problem:
  1. Since the SC-2043-SG guarantees eight analog input channels, how can I connect it to the DAQCard-1200?
  2. Signals under nonreferenced single ended (NRSE) mode share a common ground line, but can I still connect strain gages?
  3. Why am I still getting noise if each signal is isolated?



Solution:
  1. Configure your DAQCard in NRSE mode, as the SC-2043-SG can only interact with data acquisition (DAQ) devices in NRSE mode.
  2. If you directly connect signals to the DAQCard under NRSE mode, using strain gages (or any rapidly varying signal) causes significant cross-talk between your lines. However, the SC-2043-SG has its own instrumentation amplifiers. Each of the amplifiers is isolated; therefore, when the signal passes the amplifier, the amplifier "rectifies" the signal to the common ground, and then passes it through to the device. This method ensures the ground line does not move, even in NRSE mode.
  3. You must ground your unused channels together, and to EX–, especially if you are using 1200 Series devices. Because there is no path to dissipate the extra potential between the two leads of the unused channels, the actual potential between them can "float" or "rail" at maximum. This causes the instrumentation amplifier to pass on the railed value. The instrumentation amplifier has a maximum output range of ±11 V. If the amplifier passes that value to a multifunction I/O (MIO) device, which has input ranges of ±15 V, the MIO device can read the value at ±11 V and continue with the scan of the next channel. However, the 1200 Series devices have input ranges of ±5 V. Therefore, when the SC-2043-SG rails, the DAQCard-1200 receives the ±11 V signal and cannot dissipate the extra charge. As a result, each of the channels receive random offsets. To avoid this, ground the unused channels to dissipate extra charge.


Related Links: Product Manuals: SC-2043-SG User Manual
Product Manuals: DAQCard-1200 User Manual


Attachments:





Report Date: 12/13/1997
Last Updated: 08/22/2003
Document ID: 14CIIIW1

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