dads assignment 2

GROUP PROJECT Project Stage 2

48570 Data Acquisition and Distribution

Autumn 2014

Report Complied By

Benny Tantawi Swardi 11546037

Denny Gunawan Tjhong 11494921

Myo Ko Ko 11459245

48570 Data Acquisition and Distribution Project Stage 2Autumn 2014

Table of Contents1 Introduction............................................................................................................2

2 DAQ Board..............................................................................................................2

3 Analysis of open-loop characteristics.............................................................................3

4 Controller design......................................................................................................3

5 Closed-loop Control System.........................................................................................3

6 Analysis of closed-loop characteristics............................................................................4

Conclusion................................................................................................................ 6

Appendix..................................................................................................................7

Page 1 Benny T. Swardi, Denny G. Tjhong, Myo Ko Ko11546037 11494921 11459245


1 IntroductionThe main aim of this project is to regulate the temperature of a resistor with a heat-sink (see Figure 1). The temperature of the resistor R is measured by a temperature sensor mounted on the heat-sink. The measured analogue signal needs to be conditioned by an instrumentation amplifier and a low pass filter before being interfaced to an ADC, either on a PC DAQ board or Microcontroller.

In order to track the reference temperature, you need to implement control algorithms to generate a digital output signal (PWM) from the DAQ/PIC. This digital signal can manipulate a MOSFET on or off to regulate the temperature of the resistor to the desired value. In order to improve transient response of temperature regulation, a fan is also installed to cool the resistor. The fan is controlled using a digital output line from the DAQ/PIC. The fan can either be switched ON/OFF or regulated by using a PWM input.

This report includes Stage 2 of the project – LabVIEW Virtual instrument, where we are required to regulate the temperature of the resistor with a heat-sink by using LabVIEW and a Data Acquisition (DAQ) Board by using a reference voltage. To track the reference temperature we implement a control algorithms to generate digital output signals from the DAQ board. This digital signals can manipulate the MOSFETs on or off to regulate the resistor temperature to the desired value.

2 DAQ BoardThe DAQ Board is an analogue signal conditioning apparatus utilized for sampling real world signal sources and processing the sampled signal into a useful digital format which can be further utilized by using computer software, such as LabVIEW. We sampled three output signals, namely temperature sensor (from op-amp buffer), level shifter, and active filter from the Stage 1 Project and utilize them to construct a digital controller which is able to set the resistor temperature to the reference voltage which we have in the LabVIEW.



Using the pulse width modulation (PWM), the MOSFET of the resistor driver can be turned on and off. At a fixed frequency 100 Hz, MOSFET should be turned on and off. In addition, in order to control the temperature, we can change “on” width. When the duty cycle of the MOSFET (ratio of “on” width to period) increases, the temperature of the resistor will also rise. It can be noted that the logic zero state of a signal from the DAQ board corresponds to the MOSFET being ON. After that, a knob in VI is created so as to change PWM duty cycle. Therefore, it can be said that the “manual” control over the temperature is created. Moreover, the pulse width on VI also should be displayed.

3 Analysis of open-loop characteristics Before doing analysis of closed-loop characteristics, the open-loop characteristic was demonstrated first. First of all, both steady-state and dynamic characteristics were investigated, which means the input-output relationship of the steady-state and the step response of the process. So as to record the data and analysis for the process, the LabVIEW and Excel software were used. In the end the result were tabulated as below:

In order to calculate the PID parameters the Ziegler-Nichols method was used as shown below:



Since we used the PI controller in the project, the following equations were used to analyse the response of the fan and heater. First of all the variable of the response were determined as follow:

y∞=¿ steady state

y0=¿ Initial value

t 0=¿ time of changing duty from 0.2 to 0.7

t 1=¿ time for 10% of the responset 2=¿ time for 63% of the response

u∞=¿ final duty cycleu0=¿ first duty cycle

After that the value of k0 was calculated:

k o=y∞− y0u∞−uo

Then;

τ 0=t 1−t0v0=t 2−t1k p=0.9v0K0 τo

T i=3 τ0K i=K p

T i

4 Controller designAfter the results were described, the control algorithm and the parameters were selected. The method of selecting controller parameters were described below,



5 Closed-loop Control SystemFor the closed-loop control system, first the “automatic” control system in VI was created to control over the temperature. Which means that a set-point controller that utilise feedback measurements has been implemented? Next, in order to improve the transient response of the closed loop system, the fan was regulated. Moreover, the switch between “manual” and “automatic” control was also created in VI. Finally, in ideal case, the input voltages read the same value. For example, if the reference potentiometer setting corresponds to 60°C, then the outputs from Stage 1 should be calibrated to read the same temperature.

6 Analysis of closed-loop characteristics In the analysis of closed-loop, first of all, the tracking performance (the output of the active filter) and the duty cycle of the PWM waveform of the control system for reference inputs were recorded using Lab VIEW. The reference input was recorded between 30 °C and 80 °C, in steps of 10 °C. After that, an analysis to the performance of the underdamped response has been made according to its properties such as settling time, rise time, overshoot and steady-state error. In the end, all the result were tabulated as below.



Figure 2-Time Domain Controller Response



Conclusion In the report, the main aim of the projects is to regulate the temperature of a resistor with a heat sink is briefly described. Then, as a stage 1 of the project, Analogue Signal Conditioning, is specifically described. Generally, in the signal conditioning process, the driver stage, sensor stage, level shifter and active filter processing are demonstrated respectively. Moreover, a detail calculations and specific diagrams to each of the process is described and the report is written as an answering essay referring to all of the questions that are asked in the projects.



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