LabVIEW and Arduino as a gateway to PLC programming

Abstract

LabVIEW and Arduino as a gateway to PLC programmingThe key topics of an instrumentation and controls course are a) the transducers that convert thephenomenon of interest into a predictable signal b) the actuators that influence the process inquestion and c) the hardware and software that control these outputs based the measured inputs. Common candidates for these control systems are data acquisition (DAQ) systems,microcontrollers, and programmable logic controllers (PLCs). Outside of the electricalengineering technology curriculum, engineering technology students at UNC Charlotte do notcover any of these devices until senior year (if then). In a graduate course focused on facilitiesinstrumentation and controls, National Instruments DAQ systems, Arduino microcontrollers, andAllen Bradley PLCs were introduced in that order to quickly bring students up to speed on thestrengths, weaknesses, and suitable applications for each device.The graduate students in the class came from both civil engineering and constructionmanagement undergraduate programs. As such, they had limited backgrounds in electronics andprogramming. This assessment was reflected in an initial course survey where students ratedtheir abilities in electronics theory, electronics hands on, LabVIEW, and MATLAB as beingweak, slightly weak, or average (the three lowest categories on the survey). Conversely, theyrated their abilities in math and physics as being average, strong, or very strong (the three highestcategories on the survey).National Instruments LabVIEW and a NI USB-6009 multifunction DAQ were chosen as astarting platform given the graphical programming environment, readily available tutorials, andintegration with the hardware. Students were shown demonstrations involving simplebreadboard circuits before the students worked in small groups to replicate and extend theLabVIEW code and breadboard wiring to include measurements circuits with voltage dividers,RC filters, thermocouples, operational amplifiers, and controlling outputs with pulse widthmodulation and transistors.After completing the breadboard exercises with LabVIEW and the USB DAQ, they werereplicated using the Arduino 1.0 Integrated Development Environment (IDE) and an ArduinoUno microcontroller. As a high level programming language, students viewed the Arduinosketches as easy to follow given a limited introduction in lecture and access to the the Arduinowebsite (www.arduino.cc ). The abundance of published sketches made it easy for students tosee the versatility of the microcontroller platform. Other key skills that were acquired throughthe Arduino exercises included effective documentation of code, addressing inputs and outputs,and understanding the difference between analog outputs (available on the NI USB DAQ) andthe emulated analog outputs utilizing PWM (available on the Arduino Uno).Allen Bradley PLCs programmed with RSLogix software were the third platform introduced tothe students. Relay ladder logic was presented with a focus on the similarities to the graphical,‘wiring’ approach to programming. The Arduino skills of addressing inputs and outputs anddocumenting code were also reemphasized. Finally, relays were compared and contrasted to thetransistors used with Arduino, and the utility of normally open (NO) and normally closed (NC)contacts in relay ladder logic was highlighted.