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Development of a novel mechatronic system for mechanical weed ...

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4.1.2 Data acquisition<br />

4.1.2.1 Hardware<br />

Materials and methods<br />

After conditioning, signals from sensors are acquired with a notebook PC<br />

computer through a plug and play multifunctional USB DAQPad-6015 from<br />

National Instruments. The combination <strong>of</strong> DAQPad-6015 and signal<br />

conditioning unit is designed <strong>for</strong> a broad range <strong>of</strong> measurements in the field.<br />

The DAQPad-6015 consists <strong>of</strong> sixteen 16-bit analog input channels, two analog<br />

output channels and eight digital input/output channels and two counters. The<br />

<strong>system</strong> is user friendly, including NI-DAQmx measurement services s<strong>of</strong>tware <strong>for</strong><br />

simple applications and it is compatible with NI LabVIEW, LabWindows/CVI,<br />

Measurement Studio <strong>for</strong> Visual Studio .NET and other USB data acquisition<br />

devices. The maximum sampling rate <strong>of</strong> the device is up to 200,000 samples/s<br />

<strong>for</strong> a single channel.<br />

4.1.2.2 S<strong>of</strong>tware<br />

The s<strong>of</strong>tware solution <strong>for</strong> the data acquisition and plant position detection was<br />

realised with LabVIEW 8 from National Instruments. LabVIEW is a plat<strong>for</strong>m and<br />

development environment <strong>for</strong> a visual programming language commonly used<br />

<strong>for</strong> data acquisition, instrument control, and industrial automation.<br />

The visual programming language used in LabVIEW is a dataflow language<br />

also known as G code or block diagram code. Execution is determined by the<br />

structure <strong>of</strong> a graphical block diagram, which is actually the source code. This<br />

language allows parallel execution on multi-processing and multi-threading<br />

hardware. Data flow completely defines the execution sequence and it is as<br />

well-defined as with any textually coded language such as C, Visual BASIC, etc.<br />

Programs and subroutines are called virtual instruments (VI-s). Each VI has<br />

three components: a block diagram, a front panel and a connector panel.<br />

LabVIEW includes a compiler that produces native code <strong>for</strong> the CPU plat<strong>for</strong>m.<br />

The graphical code is translated into executable machine code by interpreting<br />

the syntax and by compilation. The syntax is strictly en<strong>for</strong>ced during the editing<br />

39

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