Thermal Emf; Using The Current Source; Using Digital Inputs And Outputs - National Instruments NI 435 Series User Manual

Using the Current Source

Using Digital Inputs and Outputs

© National Instruments Corporation
measured signal is outside the input range, the NI 435x may exhibit
additional errors. To minimize these errors, keep the signal source, the
NI 435x, 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 435x accessory. Avoid using dissimilar metal wires in connections.
Also, keep out temperature gradients in the space enclosing the signal
source, the NI 435x, and its accessories.
The NI 435x features a precision current source, which supplies 25 µA and
provides excitation to a total maximum resistance of 600 kΩ. The NI 4351
has an additional precision current source, which supplies 1 mA and
provides excitation to a total maximum resistance of 15 kΩ.
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.
The NI 435x features TTL-compatible digital lines. These lines can be
individually configured either as inputs or as outputs. When the NI 435x
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
Chapter 2
2-27
Operating the NI 435x Device
Measuring
NI 435x User Manual