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RMS G-Meter
Team 12 Final Report Adam Eshkanian Adam Young Takahisa Nakahama Cammi Stewart Omar Bennani Sponsored by: Greg Hoshal, Instrumented Sensor Technology Executive Summary: Ideal operating conditions for machinery and the demand for higher quality shipments has created the requirements for a simple tool to monitor vibration damage. Instrumented Sensor Technology (IST) sponsored this project to develop a real-time acceleration-monitoring instrument. The device, a “G-meter”, outputs the acceleration in units of the Earth’s gravitational pull as a peak, average, or integrated value. The design team used the highest quality acceleration sensors available to create an extremely accurate G-meter. The team’s final prototype met all specifications provided by IST. The code created for the G-meter was made in such a way that the same circuit board can support multiple models of acceleration sensors and microcontrollers. By allowing for multiple hardware devices, the design team has prepared for future hardware specification changes as well as the ability to extend the software for additional features.
Table of Contents:
- PRODUCT DESCRIPTION:.............................................................................................................................
- OBJECTIVES AND DESIGN SPECIFICATIONS:
- FINAL DESIGN IMPLEMENTATION:
- USER INTERFACE
- ALGORITHM DESIGN
- INITIALIZATION
- FINAL DESIGN PERFORMANCE:
- SUMMARY OF DESIGN TEAM ORGANIZATIONAL ROLES:
- KEY INTELLECTUAL CONTRIBUTIONS:................................................................................................
- SUGGESTIONS FOR FUTURE IMPROVEMENTS:
- CONCLUSIONS:.................................................................................................................................................
- APPENDICES:.....................................................................................................................................................
- APPENDIX A: SCHEMATICS AND LAYOUTS
- APPENDIX B: BUDGET/PARTS LIST
- APPENDIX C: SPEC SHEETS
- Accelerometer
- LCD.......................................................................................................................................................
- PIC
- REFERENCES:
Final Design Implementation: Algorithm Design There were several options to consider when converting the raw output from the accelerometer to the different RMS mode values. The first option considered was to use only calculate the information necessary for the current mode. The problem with this approach is that the data would reset every time the mode is changed. This is a bad feature if the user wants to switch modes to get different analysis of the same data. This also used extra instructions that had to be executed which made the G-meter less power efficient. To solve this we decided to calculate all the values of the different modes at the same time. It is simple, practical, power efficient, and gives the user the most flexibility when operating the device. Initialization In order to determine a reference point for the accelerometer, an initialization process is used. This process measures the output of the accelerometer for 1000 samples and calculates the minimum, maximum, and average value of the samples. By doing this, a 0G orientation is established. Further samples use this reference point to calculate the actual acceleration experienced by the device, ignoring the Earth’s gravitational pull. User Interface A simple user interface is one of the most important design requirements for the RMS G-meter. The interface consists of three major components, LCD, buttons, and casing. A basic character LCD manufactured by Matrix Orbital was chosen for its power efficiency and low product cost. A button was attached to the backlight of the LCD so that it only illuminates when the button is pressed. This allows for power conservation. The buttons are intuitive and easy to manipulate, even with gloves. A slide switch is used for controlling the power. This is to make it more difficult for the device to be turned off due to vibrations or collisions with other objects. The device packaging required that it be simple, lightweight and durable. Plastic was chosen for the material because it is lightweight, reasonably strong, low cost, and most importantly, rigid so as to not dampen the accelerometer readings. The casing also includes a compartment to allow easy battery replacement. Final Design Performance: The specification provided to the design team from Instrumented Sensor Technologies (IST) had very concise requirements. All of these requirements were met or exceeded except one, which was met as best as possible within the limitations of currently available hardware. The specification required an acceleration-sensing platform with a 5G full-scale range and 1% precision. In order to eliminate any high frequency noise, a 500Hz 4-pole low pass Butterworth filter was specified. After searching all major accelerometer vendors, only one met the accuracy specification for a 5G scale. This accelerometer has a built-in 60Hz low pass filter. After speaking to the sponsor, it was decided that accuracy was more important than the 500Hz low pass filter.
A simple user interface is important for this device. The user needs to be able to use the device to its full potential without understanding what it is doing exactly. To accomplish this, the prototype has only two buttons and a power switch. One button is for a Liquid Crystal Display (LCD) backlight, for when readings may need to be taken in darker areas. The other button is used to switch between measurement modes. With only these two buttons, the user should not have problems operating the device and recording data. Three operating modes were required in the specifications. These modes calculate the root-mean-squared (RMS) values of the peak acceleration, average acceleration, and a sum of all acceleration measured since power-on. The device computes all three of these values simultaneously so that a user can switch between modes without having to reset the device between mode selections. The team added an optional forth mode that displays the current acceleration in terms of G’s not as an RMS value so that the current acceleration of an object can be shown instantly instead of having to wait for an RMS measurement. Since one of the applications of the RMS G-meter is to be able to place the product in a shipment such as a package sent by FedEx, UPS, or freight cargo, low power was a requirement. This constraint was met by checking the power usage of each major component during the design phase. The requirement stated that the device should be able to operate for 24 hours on a standard 9V battery. The final design of the G-meter exceeds this requirement by lasting for 40 hours, nearly 60% longer than required. Summary of Design Team Organizational Roles: Omar Bennani was the team manager. He was responsible for organizing meetings, make sure that deadlines are met, and revising the project plan in response to changing circumstances. Adam Young was the webmaster. He designed and maintained team’s website throughout the semester. Adam Eshkanian was responsible for all document preparation. He put together all the documents including the proposal and group reports. Cammi Stewart took care of preparing the team for presentations. She created the presentation slides and organized what topic each member would discuss. Takahisa Nakahama was the lab coordinator so he was responsible for keeping the lab clean, and ordering parts with the ECE shop. He also made the poster displayed on Design Day. Key Intellectual Contributions: Adam Young’s main tasks were designing the circuit, low pass filter, and soldering the printed circuit board (PCB). After it was found out that the low pass filter would be unnecessary due to the built-in filter on the accelerometer, Adam helped work on the liquid crystal display (LCD). The LCD proved to be harder to program than expected so Adam worked with Cammi to extend the LCD driver into easier to use programming functions. Once the first functional prototype was created, Adam Young worked with Omar and Cammi to build a spinning arm to test the device’s accuracy. When the arm was completed, Adam took acceleration measurements from the device using a wireless video
application had a frequency greater than 60Hz the chosen model would not operate well. A simple solution would be to replace the accelerometer with one that did not have the built in filter. As stated early this is not an option in order to meet the specified accuracy so a trade off would be necessary to make this improvement. Smaller hardware could be used which would allow for an even smaller final design. With full scale PCB manufacturing a much smaller package could be chosen for the microcontroller. In conjunction with a smaller regulator and resistors the final design could be dramatically smaller. If a backlight is deemed unnecessary and a more advanced battery is chosen the design could be at least 1/3rd the size. It would also be relatively simple to design a SD card writer into the PIC to record all samples from the point that the unit is turned on. This would decrease battery life but would make it possible to view a time plot of all accelerations experienced. Conclusions: RMS G-meter measures the acceleration in the Z-axis up to 5Gs. This G-meter can be put inside or on the object of what the user wants to measure. The user will be able to see the measured values in different modes, peak, average, integrated, and raw. With its easy to read screen and simple buttons, the G-meter is very user friendly and the user will be able to easily comprehend the values displayed by the G-meter. As a result of the additional work done the user can now access simultaneous calculations for all modes instead of just one at a time. In addition, the code and design have been made so that any analog accelerometer can be used with almost any PIC microcontroller. This makes it possible for multiple models to be made for different needs with a minimal amount of overhead involved. All while being fully verified and meeting all constraints set forth by Instrumented Sensor Technologies.
Appendices: Appendix A: Schematics and Layouts Figure A: G-meter Schematic
Appendix B: Budget/Parts List Part Name Model Number Manufacturer Cost(USD) Single Cost(USD) High Volume Accelerometer MMA1250 Freescale Semiconductor
Microcontroller dsPIC30F3013 Microchip $9.20 $4. LCD Display MOP-AL082- BYFY Matrix Orbital $9.99 $9. Voltage Regulator LM7805 Fairchild Semiconductor
Casing Electric Enclosures Serpac $7.00 $7. Total Cost: $38.04 $26.
Appendix C: Spec Sheets Accelerometer
MMA
Low G Micromachined
Accelerometer
The MMA series of silicon capacitive, micromachined accelerometers feature signal conditioning, a 2 - pole low pass filter and temperature compensation. Zero-g offset full scale span and filter cut-off are factory set and require no external devices. A full system self-test capability verifies system functionality. Standard Features:
- Integral Signal Conditioning
- Linear Output
- 2 nd Order Bessel Filter
- Calibrated Self-test
- EPROM Parity Check Status
- Transducer Hermetically Sealed at Wafer Level for Superior Reliability
- Robust Design, High Shock Survivability Typical Applications: - Vibration Monitoring and Recording - Appliance Control - Mechanical Bearing Monitoring - Computer Hard Drive Protection - Computer Mouse and Joysticks - Virtual Reality Input Devices - Sports Diagnostic Devices and Systems LCD
dsPIC30F
High-Performance
Digital Signal Controller Data Sheet
Pins^ Program Memory Bytes Instructions SRAM Bytes EEPROM Bytes Timer 16 - bit Input Cap Output Comp/Std PWM A/D 12 - bit 100 Ksps UART^ SPI (^2) IC 28 24K 8K 2048 1024 3 2 2 10 ch 2 1 1
