computerized telemetry with closed loop control -...

Computerized Telemetry with Closed Loop ControlSudipta Chakraborty

Department of Electronics and Instrumentation EngineeringTechno India Group

Rajarshi De Biswas Department of Electronics and Instrumentation EngineeringSaroj Mohan Institute of Technology, Techno India Group.

West Bengal, India.

Abstract: This project focuses on long distance measurement and control; implemented by design & fabrication of a very simple low cost yet stable and powerful circuit, so as to measure a physical variable (in this case, for example, temperature) as well as to utilize it as controller of the same using wireless communication either with Centralized Control Room or with DCS.

Keywords: Semi-Automatic Closed-loop control, On-Off with threshold, Temperature monitor, DCS.

I. INTRODUCTION

There are many important variables in process plant like pressure, temperature, flow, level etc. which are required to be measured & controlled precisely in order to obtain better quality of product, lesser cost with better safety of operation. Designing a controller involves selection of sensor, calibration, adlibbing control algorithm, implementation of control loop and further workarounds, if required.

The rest of this paper has been organized in the following parts:

2. Proposal of simple hardware design circuitry.3. Experimental application.4. Algorithm for software development.

II. PROPOSAL OF SIMPLE HARDWARE DESIGN.A) Primer:

‘Simplicity is the soul of design’, to make the system cost effective, responsive and yet stable enough, we had to focus on designing the hardware part (i.e. the local sensor and indicator) in the simplest way. We, in our prototype circuitry had used only an IC based sensor, a couple of MCU’s, one LCD and few external passive components. Following is the block diagram of the various units.

International Journal of Innovations in Engineering and Technology (IJIET)

Vol. 2 Issue 4 August 2013 115 SSN: 2319-1058

Figure 1: the Block Diagram.



B) Briefing of each Module:

Figure 2: Identification of each module.

C) The detailed circuitry:,

To design and fabricate a Microcontroller based temperature indicating & monitoring system we require to interface an ADC and an LCD with Microcontroller, which are described below.

1. LCD display is used here to display the measured variable, which is easier to interface with the microcontroller and it also has minimum number of pins (11) to connect with the microcontroller. To interface the LCD display with the microcontroller we have connected the port 2 and port 3 of 89C51 with the LCD. The pins 7-14(D0-D7) of LCD are connected with port 2 (21-28) of microcontroller and the pins



4, 5, 6 (RS, R/W, EN) of LCD are connected with port 3.7, port 3.6, port 3.5 (17, 16, 15 pins) of microcontroller. Pin-1 is connected with the GND, and pin-2 is connected with the +5v, and pin 3 is connected with the contrast adjustment circuit.

2. To interface the ADC with the Microcontroller we connect P1 with the o/p port of ADC as an input port. CSP3.1 AND P3.2 respectively. To start the operation we configure P3.2 (INTR) as an input port pin signal. After that we send a low to high pulse to start conversion. After that we poll the INTR (P3.1) to check the end of conversion. After ensuring a low logic from port P3.1 we send active low RDdigital output, and we save this data to the accumulator.

The circuit diagrams are as follows:

Figure 3.1: The remote Sensor and Display Circuit. (Click on Picture to Enlarge)

1. A simple PIC based HID-pnp Model (Generic human Interface Parser) available as online resource for entry level PIC projects, has been modified by ourselves here to work cumulatively as

i. A/D Converter to process the sensor data; ii. USB Bridge to communicate with the Local Computer;

iii. Control Action Signal Career and Driver of the FCE.



The Main workflow of the system is as follows:

§ The sensor data is tapped once before the 0804 A/D converter and is fed directly to the ADC0 Pin of the PIC, this RAW data is forwarded at once to the Control Software of the host computer which itself performs necessary signal conditioning, averaging, and reproduction of the same.

§ After the aforesaid operation, the temperature is displayed on the PC screen both digitally and in a 2° to 100° Centigrade temperature bar graph scale.

§ Besides displaying, the software continuously monitors the changes in the temperature status, and compares it with a User Defined Set Point Value. As soon as it reaches One Degree over the set point, the system triggers the Final Control Element, and keeps it running until the temperature is Five Degrees below the set point.

§ The software also encloses an option for Manual Intervention- whenever initiated, the FCE auto triggering gets halted, and however, monitoring of temperature still goes on.

§ To make the communication bidirectional, a push to on momentary alarm button is placed in the PIC board, which, when pressed, notifies a signal in the software screen.

§ The unit is also capable of being shared over Ethernet via any USB sharing protocol, like USBIP, USB over Network etc.

Figure 3.2: The PIC based Data Acquisition system. (Click on Picture to Enlarge)



III. EXPERIMENTAL ARRANGEMENT

A. Sensor Calibration:

To calibrate the sensor, we have to compare its output at different common ambient temperature with the output of a pre-calibrated (standardized) instrument. In order to do the same, following steps are performed: 1. First the sensor is subjected to the exposure of normal ambient condition. 2. The Output of the Sensor is registered. 3. In the same ‘as is’ situation, a standard calibrated instrument is introduced. 4. The output of the second instrument is also registered in a separate field. 5. The above process is repeated in different temperature levels. 6. Two different outputs are compared. 7. A standard deviation curve is generated.

Table of Sensor Calibration:

TEMP RATED PRACTICAL DEVIATION PRECENTAGE ERROR

C V V V

10 0.1 0.14 0.04 40

20 0.2 0.21 0.01 5

30 0.3 0.32 0.02 6.666666667

40 0.4 0.39 -0.01 2.5

50 0.5 0.47 -0.03 6

60 0.6 0.58 -0.02 3.333333333

70 0.7 0.71 0.01 1.428571429

80 0.8 0.81 0.01 1.25

90 0.9 0.91 0.01 1.111111111100 1 1 0 0



Figure 4. Standard Deviation Curves.



IV. SOFTWARE DEVELOPMENT: FLOW CHARTSA. The 8051 Firmware:

(Click on Picture to Enlarge)



B. The PIC Firmware:



C. The PC Interface:

(Click on Picture to Enlarge)



V. CONCLUSIONCompared with the present days’ telemetry gadgets, this project deals with a rather old-fashioned concept, for the sake of simplicity and cost-friendliness, however, the precision and other qualities of service are not far compromised. Thanks to the PC based control UI, the system can be coupled either with any type of network frameworks (i.e. LAN, WAN VPN etc.) or with custom DCS panels. The provision for manual intervention is also there to handle uninvited or hasty situations.

REFERENCES

[1] Modern Electronics Measurements and Instrumentation, by S.K. Singh.[2] Automatic Control Systems, by Benjamin C. Kuo.[3] The Encyclopedia of Electronic Circuits, by Rudolf. F. Graf.[4] Data Communication and Networking, by Behrouz A Forouzan.[5] Modern Electronic Instrumentation and Measurement Techniques, by Helfrick & Cooper.[6] Microcontrollers: Architecture, Programming, Interfacing and System Design, by Raj Kamal.[7] http://ieeexplore.ieee.org[8] www.pyroelectro.com[9] http://www.microchip.com[10] http://msdn.microsoft.com



computerized telemetry with closed loop control -...

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