T
F
and T
C
are the temperature readings in degrees Fahrenheit and degrees Celsius,
respectively.
Note
Use the average of a large number of samples to obtain the most accurate
reading. Noisy environments require averaging more samples for greater accuracy.
Connecting Nonreferenced or Floating Signal
Sources to Analog Inputs
A floating signal source is a signal source that is not connected in any way to the building
ground system but has an isolated ground-reference point. If an instrument or device has an
isolated output, that instrument or device falls into the floating signal source category. Some
examples of floating signal sources are outputs for the following: thermocouples,
transformers, battery-powered devices, optical isolators, and isolation amplifiers. The ground
reference of a floating source must be tied to the ground of the MIO DAQ device to establish a
local or onboard reference for the signal. If this reference is not established, erratic readings
from the board will occur.
Differential Inputs
To provide a return path for the instrumentation amplifier bias currents, floating sources must
have a 10 to 100 kΩ resistor connected to the AI GND signal line on one input if DC-coupled,
or both inputs if AC-coupled. For detailed information on connections to floating signal
sources and differential inputs, refer to your device documentation.
Single-Ended Inputs
When measuring floating signal sources, configure the MIO DAQ device to supply a ground
reference. Therefore, configure the MIO DAQ device for referenced single-ended (RSE) input.
In this configuration, the negative input of the MIO DAQ device instrumentation amplifier is
tied to the analog ground. For detailed information on connections to floating signal sources
and single-ended inputs, refer to your device documentation.
Connecting Ground-Referenced Signal Sources
to Analog Inputs
A grounded signal source is connected in some way to the building system ground; therefore,
the signal source is already connected to a common ground point with respect to the MIO
DAQ device (assuming the host computer is plugged into the same power system).
Nonisolated outputs of instruments and devices that plug into the building power system fall
into this category.
NI SCB-100 Installation Guide and Specifications
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© National Instruments
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