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A digital multimeter (DMM) is a tool that is used in order to troubleshoot wiring and/or components to determine faulty equipment. It is used in various applications, from automotive, aircraft, minor electronic repair and other purposes. The DMM can be used to measure voltage, current, resistance, test diodes and the Hfe test. Voltage uses work (W) which is equal to the joule (J). The charged particles require work to move from the negative end to the positive end of the circuit. Which then is equal to the Force (N) times the Distance (meters). Current is generated when electrical movement is initiated. Current is represented by the SI unit Ampere (A). Resistance is the act of opposition of electron flow and makes it possible to cause current flow. The SI unit for resistance is the capital omega ( ). The diode test decides whether the diode in the given circuit functions on a forward voltage drop between 450 to 900 mV. The reverse voltage check results in a good diode if the indication reads a 1 in the most significant digit and blanks the remaining digits, it will read bad if the display reads “000″ or some other value in the display (DMM manual). Hfe is the forward current gain of the transistor.

The block diagram in figure one shows a brief description how the DMM functions. The selector switches is the switch on the outside of the DMM, the only switch that you can manipulate on the outside in order measure what you need. If the switch is selected on the outside to read DC voltage the information that is received is sent to voltage divider and then sent to which in turn tell the A/D converter to display in a digital format for easy understanding. If the selector switch is set to the AC position then the AC converter has to convert that input and then to the A/D converter for digital display. The switch could then be positioned to read resistance, in that case the ohms converter, converts the input into and readable entry in order to be displayed in the digital readout. If high current is needed to be measured then the current shunt is enabled to tell the selector switches inside to read high current and change the reading to display this.

A couple of interesting aspects in the assembly of the DMM are as follows: I decided against soldering all the smaller components first and then determined that I would solder the larger components. The reason that I did this was because I wanted to install the more difficult ones first just in case I ran into any problems in the beginning it would be easier to fix. If all the components were installed the likely-hood of easily repairing the situation would be difficult. I found it a little bit easier to measure each resistor individually and install one at a time by checking the color code and the resistance to ensure I was installing the correct component in the correct location. I also found by doing that it opened a lot more ways to improve on the soldering techniques because each individual solder joint was meticulously managed. Some of the directions were not so clear on the exact specifications of the components, because it showed in particular the input sockets going in a certain direction and did not give a detailed explanation exactly how it was installed. So in order to rectify this I had to “size” up the component inside the case and determine whether the pictorial representation was up to the same level and if I should do exactly what the book had said. Ultimately it was apparent that the input sockets had to be installed the way the book specified but it turned out the book did perform an unacceptable way to describe it. One note in particular that I could suggest for future assembly on this project is to make sure that the zebra board is free of debris. After I had completed my project one of the LCD segments was not correctly displayed in the LCD. So I took it apart a couple of times and finally corrected the malfunction by cleaning off the debris that was on the zebra board and the LCD contacts. The zebra boards conduct form top to bottom, essentially from the circuit board to the LCD. This current is then supplied to the LCD in order for it to display the needed information.

I thought this was a great project and I expect to enjoy the rest of the building and maintain the enjoyment throughout the cycle of evolution.

References

Digital Multimeter assembly and instruction manual.

Model M-1006k, Elenco Electronics, Inc.

Schaum’s Outlines: Basic Circuit Analysis (Second Edition) by John O’Malley

  • Chapter 1: Basic Concepts

  • Chapter 2: Resistance

Schaum’s Outlines: Basic Electrical Engineering (Second Edition) by Jimme J.

Cathey and Syed A. Nasar

  • Chapter 1: Circuit Elements and Laws


~~~~~Written by Tom -Visit Website~~~~~
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