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Chapter 2
Operating the NI 435x Device
©
National Instruments Corporation
2-27
measured signal is outside the input range, the NI 435
x
may exhibit
additional errors. To minimize these errors, keep the signal source, the
NI 435
x
, and its accessory away from strong AC magnetic sources and
minimize the area of the loop formed by the wires connecting the signal
source with the accessory. Choosing the notch filter frequency of 10 Hz
provides the best AC noise rejection. If the peak value of the measured
voltage is likely to exceed the selected input range, select the next higher
input range.
Thermal EMF
Thermoelectric potentials or thermal EMFs are voltages generated at the
junctions of dissimilar metals and are functions of temperature. Thermal
EMFs in the source generating the signal can introduce errors in
measurements that change with variations in temperature.
To minimize thermal EMFs, use copper wires to connect the signal to the
NI 435
x
accessory. Avoid using dissimilar metal wires in connections.
Also, keep out temperature gradients in the space enclosing the signal
source, the NI 435
x
, and its accessories.
Using the Current Source
The NI 435
x
features a precision current source, which supplies 25
µ
A and
provides excitation to a total maximum resistance of 600 k
Ω
. The NI 4351
has an additional precision current source, which supplies 1 mA and
provides excitation to a total maximum resistance of 15 k
Ω.
These resistances can be in the form of RTDs, thermistors, or any other
resistor. The calibrated value of the current source is stored on-board, and
NI-DAQ uses this precise value in its computations. Refer to the
Temperature with RTDs and Thermistors and Measuring Resistance
section for details on how to use this current source.
Using Digital Inputs and Outputs
The NI 435
x
features TTL-compatible digital lines. These lines can be
individually configured either as inputs or as outputs. When the NI 435
x
powers on, these digital lines are configured as high-impedance inputs.
You can use the DIO lines as an interface to control processes; control
events such as turning on and off heaters, relays, motors, or lights; generate
patterns for testing; and communicate with peripheral equipment. If the