Calibrated Tilt Monitoring System Using Fpga

Published Date: 02 Nov 2017

Abstract: Measurement of tilt is having a very much importance in the applications such as railway track monitoring, mining, aviation, tunneling, bridge and dam monitoring system, etc. The tilt is measured in terms of degrees and is made with respect to the original tilt of the surface on which the meter is kept. This paper proposes an embedded tilt measurement system, which uses a level sensor, A/D converter, Spartan 3 board and a controller designed in FPGA using VHDL with the help of Xilinx software. The proposed model of the tilt measurement system would measure the tilt based on an initial calibration and the Reference tilt set at the beginning. Here we have an output tilt which is available in degrees and it changes as per the input changes .The controller designed using VHDL would sense the changes in the inputs which is the change in the tilt, measured as 8 bit values (measured by level sensor and fed to Spartan 3 board via A/D converter). Accordingly the tilt will be displayed using LCD module on Spartan 3 Board. The proposed system can be calibrated to get the specified precision in calculating the tilt. The system is able to calibrate the tilt up to required precision. The model will be scalable so that the input and output ranges could be easily changed as per the situation demands.

Keywords: A/D converter, LCD module, VHDL, sparten 3 FPGA, ModelSim.

1. INTRODUCTION

System is used to capture and calibrate the small changes in the level of the surface on which it is mounted, with respect to its initial position. The tilt or deflection of the system at its initial position is called as reference tilt and is always considered as 0‟ degree the designed system is a multipurpose embedded system for the measurement of tilt based on SPARTAN 3 FPGA. It has very much application in the field of aviation, robotics, dam monitoring system, bridge monitoring system, etc.

This system mainly consists following parts ,level sensor, Simple A/D converter, SPARTAN 3 Board Here a Tri-axial sensor using a multi turn potentiometer pot is use to serve the purpose of capturing the inclination of surface[1].

The output of a sensor is a voltage i.e. an analogue value which is dependent on the level or position of the surface on which it is mounted.

If there is change or deflection in the level of surface the output of the sensor will vary depending on the amount of variation in the level of surface[1]. Output of the level sensor is fed to the simple A/D converter which is used to convert the analog value into corresponding 8 bit value i.e. the digital data.

This digital data corresponds to the amount of the changes in the level of surface which will be dependent on the o/p of the sensor (analogue value) fed to it. The O/P of the A/D converter is fed to the SPARTAN 3 board .

The controller will display these values on the display provided on SPARTAN 3 boards in required format as e.g. TILT: 019.00 DEG. This system is capable of displaying the tilt in the range of 0 to 255 degrees[3].

2. PROPOSED BLOCK DIAGRAM

Spartan 3 FPGA board

Fig 1: Block diagram of tilt measurement system

2.1 Sensor

The Tilt is a static measurement where gravity is the acceleration being measured.

Therefore, to achieve the highest degree resolution of a tilt measurement, a low-g, high sensitivity accelerometer is required. Sensor arrangement is used to sense the surface deformation or change in the position of object on which the tilt meter is mounted with respect to its reference position. We are using gravity based resistive sensor[2]. When tilt occurs resistance of the potentiometer changes. According to this the output voltage changes which is given to A to D converter, which coverts analog value to digital value and then it is given to expansion header. We choose a multi-turn for more power, better resolution, linearity, and stability than a single turn.

2.2 ADC 0808

General Description

The ADC0808, data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator ,a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals.

The device eliminates the need for external zero and full-scale adjustments. Easy interfacing to microprocessors is provided

by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs.

The design of the ADC0808, ADC0809 has been optimized

by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808, ADC0809 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications. For 16-channel multiplexer with common output (sample/hold port) see ADC0816 data sheet. (See AN-247 for more information.)

Features

â–  Easy interface to all microprocessors

â–  Operates ratiometrically or with 5 VDC or analog span adjusted voltage reference

â–  No zero or full-scale adjust required

â–  8-channel multiplexer with address logic

â–  0V to VCC input range

â–  Outputs meet TTL voltage level specifications

â–  ADC0808 equivalent to MM74C949

â–  ADC0809 equivalent to MM74C949-1

BLOCK DIAGRAM OF ADC 0808

Fig 2: block diagram of ADC 0808

2.3 LCD MODULE

LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data.

The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. Click to learn more about internal structure of a LCD.

2.4 Working Principle

The designed system is a multipurpose embedded system for the measurement of tilt based on SPARTAN III FPGA. It has very much application in the field of aviation, robotics, dam monitoring system, bridge monitoring system, etc. This system mainly consists following parts ,level sensor, Simple A/D converter, SPARTAN 3 Board Here a gravity based resistive sensor using a multi turn potentiometer pot is use to serve the purpose of capturing the inclination of surface.

The output of a sensor is a voltage i.e. an analogue value which is dependent on the level or position of the surface on which it is mounted.

If there is change or deflection in the level of surface the output of the sensor will vary depending on the amount of variation in the level of surface. Output of the level sensor is fed to the simple A/D converter which is used to convert the analogue value into corresponding 8 bit value i.e. the digital data. This digital data corresponds to the amount of the changes in the level of surface which will be dependent on the o/p of the sensor (analogue value) fed to it[3]. The controller will display these values on the display provided on SPARTAN 3 boards in required format as e.g. TILT: 019.00 DEG. This system is capable of displaying the tilt in the range of 0 to 255 degrees.

3. QUANTIZATION STEP IN A8DC080

4. CONCLUSION

This paper demonstrate the Embedded controller for tilt measurement where an

external sensor is used for tilt measurement .The sensor has 5 outputs and gives the tilt in digital angle format .Being a 5 bit output device, it can measure tilt to an accuracy of 360/2^5 = 11.25 degrees, each bit indicates a 11.25 degrees approximate tilt, from the reference tilt. To further elucidate the point let us take an example, the output 00110 indicates a tilt of 6 * 11.25 = 67.25 degree tilt from the reference tilt. This measured tilt will be given to the Spartan 3 Board and the tilt would be displayed on the LCD.The LCD data pins as present on the board are used. The expansion slot 1 is used as the slot to take input from the tilt meter sensor[3]. The VHDL code that will be burnt inside the Cyclone chip would convert this value into a proper tilt value and then produce the output accordingly. The output produced out of this conversion would be shown on the LCD screen. The LCD operates on a 27 states, 11 states are used for initialization and the other 16 states write a single line output on the LCD in the form of ASCII HEX characters.