# Design and Implementation of an Analog Multimeter Using Permanent Magnet Moving Coil (Pmmc) Meter Movement

KEVIN BARRAQUIAS DELOS SANTOS

2008-19116

MARX MARJONEL BIBAR JOVELLANO

2008-30845

PRINCE TEOMEL GUSTO MATEL

2008-18863

SUBMITTED TO THE FACULTY OF THE

COLLEGE OF ENGINEERING AND AGRO-INDSUTRIAL TECHNOLOGY,

UNIVERSITY OF THE PHILIPPINES LOS BAÑOS,

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREE OF

BACHELOR OF SCIENCE IN ELECTRICAL ENGINEERING

OCTOBER 2010

I. INTRODUCTION

An analog multimeter is a device that is composed of various meters combined. Such instrument can measure resistance, voltage and current. It is commonly known as volt-ohm meter or VOM. This device can also determine the continuity in a circuit and it measures with high accuracy. In this project, a VOM was built using the given parameters and tested it in various circuits. The knowledge in building this kind of instrument is very helpful for the students. A. OBJECTIVES OF THE STUDY

A.1 GENERAL OBJECTIVE

This project intends to design and to implement an Analog Multimeter using a Permanent Magnet Moving Coil (PMMC) meter movement. A.2 SPECIFIC OBEJECTIVE

The specific objectives are:

* To determine the internal resistance of the PMMC meter movement using variable resistor method. * To compute for the shunt resistance of 10mA and 100mA range ammeter. * To compute for the shunt resistance of 5 volts and 30 volts range voltmeter. * To determine the shunt resistance of ohmmeter with a 1.5 voltage. * To make a schematic diagram of the multimeter circuit.

B. SCOPE AND LIMITATIONS

* PMMC meter movements or the panel meter in the analog multimeter will not work correctly if directly connected to alternating current, because the direction of needle movement will change with each half-cycle of the AC. Permanent-magnet meter movements, like permanent-magnet motors, are devices whose motion depends on the polarity of the applied voltage or the direction of the current. Hence, it can only measure DC currents, DC voltages and resistances. * Have no scaling; the probability of parallax error is very high. * 100mA range ammeter is not functioning

* Ohmmeter is not functioning well

* Not portable since the case is not so handy

II. METHODOLOGY

A. MATERIALS

Table 1. Materials used for the project and their corresponding costs Material| Quantity| Cost/unit| Total cost|

100-A panel meter| 1| P230.00| P230.00|

6-position 2-pole switch| 1| P45.00| P45.00|

Pair of probes| 1| P35.00| P35.00|

Pcb| 1| P75.00| P75.00|

1-Ω resistor| 4| P1.00| P4.00|

1.2-Ω resistor| 4| P1.00| P4.00|

100-Ω resistor | 3| P1.00| P3.00|

330-Ω resistor | 1| P1.00| P1.00|

820-Ω resistor | 3| P1.00| P3.00|

10-kΩ resistor | 7| P1.00| P7.00|

15-kΩ resistor| 3| P1.00| P3.00|

470-kΩ resistor| 2| P1.00| P2.00|

TOTAL| P412.00|

B. METHODS

This project of designing and implementation of an analog multimeter consists of constructing and calibrating a Direct Current (DC) voltmeter, a DC ammeter, an ohmmeter. Determining the internal resistance of the PMMC meter movement was the first step. The panel meter was connected in series with a DC voltage source and a potentiometer as shown in Figure 1 to determine its internal resistance.

Fig. 1. Set-up of the circuit for determining the internal resistance Next, the internal resistance of the panel meter was measured using variable resistance method. Subsequently the internal resistance was computed and recorded using Equation 1: RIN = RHS – 2RFS [Equation 1] *

Where:

RIN - internal resistance of the panel meter

RHS - resistance of potentiometer at half scale

RFS - resistance of potentiometer at full scale

The next step was calibrating the DC ammeter. The values of shunt resistors were necessary for current ranges of 10 to 100 mA since the panel meter used has a maximum...

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