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The design and implementation of an autoranging multimeter. - Coggle…
The design and implementation of an autoranging multimeter.
Safety Issues
sdp-k1 microcontroller
is SIL ready : IEC 61508 SC3 compliant, which means it passes an international functional safety standard
TUV Rheinland certified
a TÜV certification ensures that a product has been tested for safety. It complies with the requirements of national, regional, and international regulations. It assures consumers that the product has been checked thoroughly for any defects or potentially hazardous materials.
X-CUBE-STL library
Software-based diagnostic suite designed to detect random hardware failures in STM32 safety-critical core components (CPU + SRAM + Flash memory)
Warnings given :
not intended for use as a
consumer end product or as a portion of a consumer end product
designed to be used solely in a laboratory environment.
does not include a
shielded enclosure
therefore may cause interference to other
electrical devices in close proximity.
This board should not be
used in or near any medical equipment or RF devices.
unused boards are to be stored in the protective shipping package.
ADALM2000
The Restriction of Hazardous Substances Directive
damage source ( batteries/computer)
Lifecycle Implications
SDP-K1 Evaluation board
Procedure For Return of ADI Evaluation Boards in accordance with requirements of Waste Electrical and Electronic Equipment
ADALM2000
Procedure For Return of ADI Evaluation Boards in accordance with requirements of Waste Electrical and Electronic Equipment
ADALP2000
WEEE dropoff recycling point or Civic Amenity Site
RoHS
- Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment
WEEE
- Waste Electrical and Electronic Equipment is electrical and electronic equipment that is broken or unwanted
If battery powered, mywaste (a WEEE scheme) has battery recycling facilities for the utilization of the public.
Marketability
Commerical Use as desktop Multimeter
Opportunity to add further features remains open
Integration with App
Easy Access
User Friendly Interface and Operation
Bluetooth Integration
Allows for wireless connection
Bluetooth is a widespread connection option
Convenience for Users
Quick and Easy Operation
Allows Distribution through major app outlets
Play Store (Android)
App store (IOS)
Low Power Operation
USB powered at 5V (+/- 10%)
DC Jack powered at 7V - 12V
Multi-variable Analysis
Resistance
Voltage
Frequency
Capacitance
Current Market Leaders in Digital Multimeter Development
Fluke Corporation (US)
Tektronix (US)
Keysight Technologies (US)
Yokogawa (Japan)
Gossen Metrawatt (Germany)
Market Demand
Asia Pacific is expected to be the largest digital multimeter market during the forecast period
Forecast Period 2019–2024
multimeter with infrared sensors for thermal imaging
Requirements
Capacitance
Error Analysis
Measure multiple capacitors using the in lab LCD
Measure the same capacitors using the project multimeter
Quantify the difference in capacitance measurements
Take the difference as a margin for error of the project multimeter capacitance measurements
Accuracy
Avoid overloading (supplying multimeter with difficult to measure values/out-of-range values)
Utilize multiple resistors that can accommodate capacitors from nF to uF capacitance to result in a friendly time constant reading (too small/too large)
Calibration
Minimise any measurement uncertainty by ensuring the accuracy of test equipment
Run a calibrating test code before a capacitance is measured to ensure system constants are as they should be.
If test is not passed, user is alerted to issues within the system.
Precision
Ensure the value of resistance is known and calibrated (possible testing required)
Ensure input voltage is known and calibrated (possible testing required)
Ensure code corresponds to the known values
Implementation
𝝉 = R ✕ C
𝝉 = Duration of capacitor charging to 63% of the input voltage.
Frequency
Error Analysis
Error Analysis will be conducted by comparing frequency recorded using digital multimeter to frequency recorded via desktop multimeter
Compare Digital Multimeter frequency reading to lab oscilloscope reading
Precision
Ensure clock signal is known and calibrated
Ensure Voltage Peak Detector is calibrated, accurate and operational
Ensure code corresponds to known values
Accuracy
Increasing gate time improves accuracy as automatic arming mode is inaccurate
To ensure the most stable operation of the crystal, keep your counter in a spot where you don't have to unplug it, so it can alternate between on and standby mode.
The Quality of the timebase and how often it is calibrated will affect measurement accuracy
Trigger error is the RMS noise of the instrument's input amplifier and the RMS noise of the input signal over the bandwidth of the instrument. This variable affects accuracy of frequency counters
When measuring a low frequency signal limiting the bandwidth will eliminate high frequency noise.
The skew and/or jitter that occurs between two independent timebases will add to error. Therefore the design should lock all timebases to a single clock.
Calibration
The frequency component of the device will be calibrated by adjusting the time period over which frequency is measured
Test components used for calculating frequency
Implementation
Multiple Methods of Measuring Frequency
Different Methods of Recording Frequency
Input through transistor while internal timer takes constant time readings
1 Period = Time from 1st Switch On to 2nd Switch On
Frequency = 1/Period
Frequency Counter 3 ways to generate Square Clock Signal
Square Wave Generator using 555 Timer IC configured as an Astable Multivibrator.
duty cycle of about 99%
duty cycle depends only on the value of the threshold and discharge resistors
D = (R1+R2)/(R1+2R2)
Internal Clock Signal
Call upon internal clock timer
Use Diode peak detector and measure time elapsed between cycles
Schmitt-trigger inverter, with a capacitor and resistor.
Frequency = 1/Period
Definition = (Trigger Level Crossings)/(time in seconds)
Voltage
Error Analysis
Analyze voltage values obtained when testing using Laboratory equipment and values when using the device produced in this project
Take the differences in the values obtained as your margin of error, convert this difference to a percentage and state this tolerance in the spec sheet
Identify the cause of error and rectify where possible
Precision
Ensure the resistors used are the same value that they are rated as in the ADALP kit datasheet
Limit the power supply so that it is limited to -5 -> +5
Ensure that the code uploaded to the microcontroller is correct and that the correct resistance values are declared in the code
Test circuit in Laboratory using the highly accurate equipment available
Calibration
Measure the resistors used to make the voltage divider in the Engineering lab to verify the resistance of the component is as described in the ADALP Kit
Set up the voltage divider circuit in the Engineering lab. To ensure the highest degree of accuracy, use the power supply and multimeter available in the lab to perform the voltage measurement
Repeat this procedure but this time use the voltmeter constructed as part of this project
Compare the results from both procedures
Implementation
Printing results to Serial Monitor
Accuracy
Display voltage to two decimal places on serial monitor
Ensure input voltage does not exceed +-5V as this device is rated to measure voltages from -5 -> +5
Do not leave the device plugged into power for longer than needed
excess heating of resistors can lead to increased resistance as the atoms begin to vibrate, making it difficult for electrons to flow
use floating point numbers in c++ code
Floating point numbers can be processed quicker than doubles
Resistance
Error Analysis
Measure the resistance in the lab. Then measure them using our ohmmeter that we have created. measure the difference the two sets of results
From this we should be able to establish an approximate value for the margin of error of our ohmmeter
Precision
The resistance will be calculated using a similar value to the resistor that we are trying to find
once we get an initial estimate for the resistance, our reference resistor (R1) will be replaced by another resistor with a similar value
Calibration
Measure multiple resistances in the lab. Then measure them using our ohmmeter that we have created. measure the difference the two sets of results, the differences should be minimal.
Accuracy
ensure you don't take too long to get a reading for the resistance, as the current flows through the resistor for a prolonged period of time, the temperature of the resistor will increase, changing its value of resistance
Implementation
Multiple ways to measure an unknown resistance
V = IR
Voltage Divider
we can know Vin, Vout, and R1
To calculate for R2, manipulate the voltage divider formula to get R2 by itself
1 more item...
Wheatstone Bridge
More difficult to implement. But is more accurate than a voltage divider
If current can be measured
1 more item...
Team Oraganisation
John
Frequency
Code
Implementation
Explanation
Requirements
Technical Report Writeup
Marketability
Amy
Capacitance
Code
Implementation
Explanation
Requirements
Technical Report Writeup
Lifecycle Implications
David
Voltage
Implementation
Code
Explanation
Requirements
Technical Report
Cost Implications of Project
Ciaran
Technical Report Writeup
Safety features
Resistance
Code
Implementation
Explanation
Requirements
Cost Implications
Minimizing total cost is optimal
Reusing components rather than purchasing new components
Use components from ADALP Kit or from Electrical Engineering Labs
Adhering to the WEEE Directive
Simplify design to require less components to perform required task
Dedicate plenty of time to design and review of circuits
Team members can work together to analyze each others circuits to streamline design
Only connect the device to power when it's in use
Reduces overall electricity use
may reduce electricity bill
Reduce cost by trying to fit all circuits onto one breadboard
