3 ½ DIGITAL MULTIMETER

SUBMITTED TO: SIR AKLAQ ALI KHAN

GROUP MEMBERS:NADIA SHAUKATSEHRISH KHANFARAH RIAZSADIA GUL

DEFINITION:A meter is a measuring instrument.

An ammeter measures current,

a voltmeter measures the potential difference (voltage) between two points,

and an ohmmeter measures resistance.

A multimeter combines these functions, and possibly some additional ones as well, into a single instrument.

There are two types of multimeters Analog & Digital

We have made a 3 ½ digital multimeter.

Modern multimeters are often digital due to their accuracy, durability and extra features. A digital multimeter displays the quantity measured in a number.

What 3 ½ means???The term 3½ digits refers to the number of

digits displayed on the display of a multimeter.

The three full numeric characters on the right can show any value from 0 through 9, but the leading (most significant) digit can be only 0 or 1, and is called the “½ digit”. It can display numbers from 0 to 1999. It is also known as 2000-count DMM.

There are 2 styles of multimetersSwitched:Manually switch between ranges to get most accurate reading.

Auto Range:Switches between ranges automatically for best reading.

Both of these styles work the same.

COMPONENTS:

COMPONENTS:Resistors (0.25W carbon)820 grey red brown............. R3 ..................................127K red violet orange ........ R2,5,6 ............................347K yellow violet orange ... R1 ..................................1100K brown black yellow.. R4 ..................................11M brown black green....... R7 ..................................1

COMPONENTS:Capacitors100pF 101 ceramic ............. C3 ..................................1100nF 104 monobloc......... C1,2 ...............................2220nF 224 monobloc......... C5 ..................................1470nF 474 monobloc......... C4 ..................................1SemiconductorsBC547, NPN transistor....... Q1..................................17106 IC............................... IC1.................................1

3 ½ Digit LCD A/D converter

COMPONENTS:MiscellaneousTrimpot, 200W.................... P1 ..................................1Liquid Crystal Display........ LCD...............................1

3 ½ digit, VI-302-DP-RCIC socket, 40 pin.........................................................2

For mounting IC1 and LCD9V battery snap...........................................................1PCB, K127 .................................................................

CIRCUIT DIAGRAM

CIRCUIT DESCRIPTION:DMM is essentially an Analog to digital converter (A/D)

with a digital display.IC 7106:Our main component is IC-7106IT contains in it all the active circuitry for a 31/2 digit panel

meter (DPM) in a single chip. It was designed to interface directly to a liquid crystal display (LCD).

It automatically detect polarity, show positive and negative values, have much better overload protection, and offer automatic as well as manual range selection options.

CIRCUIT DESCRIPTION(cont…)We use a few additional external passive components with

7106 chip to make our DIGITAL multimeter.The heart of the meter is the A/D converter built into the

7106. It uses a dual slope conversion technique. It relies on the charging and discharging of an integrating capacitor and having a counter count when the capacitor voltage is above a set value.

In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal.

CIRCUIT DESCRIPTION(cont…)Dual slope conversion technique:

MULTIMETER AS An AMMETER:Ammeter mode measures current in Amperes. To

measure current you need to power off the circuit, you need to break the circuit so that the ammeter can be connected in series. All the current flowing in the circuit must pass through the ammeter.

Multimeter As An Ammeter(cont..):Meters are not supposed to alter the behavior of the circuit, so

the ammeter must have a very LOW resistance. The diagrams below show the connection of a multimeter to measure current.

Multimeter As An Ammeter(cont..):The current must be converted into a voltage

using a shunt resistor. The voltage divider resistors RA and RB are not used. The principal is shown in Figure 6.

MULTIRANGE AMMETER:

MULTIMETER AS A VOLTMETER:To use a multimeter as a voltmeter it is connected in parallel between the two points where the measurement is to be made. The voltmeter provides a parallel pathway so it needs to be of a high resistance to allow as little current flow through it as possible.

In our meter VREF is set to 100mV but is adjustable from 89 - 107mV

To measure voltage greater than 200mV an input voltage divider is required

MULTIRANGE VOLTMETER

MULTIMETER AS A OHMMETERPower always has to be offComponent has to be removed from circuitStart at lowest Ohm setting

RESOLUTION AND ACCURACY:The resolution of a multimeter is the smallest part

of the scale which can be shown.The three full numeric characters on the right can

show any value from 0 through 9, but the leading (most significant) digit can be only 0 or 1, and is called the “½ digit”. It can display numbers from 0 to 1999. It is also known as 2000-count DMM.

The larger number of counts should translate into higher resolution, and usually DMMs with a higher resolution have higher accuracy. However, DMM accuracy also depends on other design factors

Accuracy specifications: ±(% of reading + number of LSD)

Reading = the true value of the signal that the DMM measures

LSD = least significant digit

ANY QUESTIONS????

MAY ALLAH BLESS US!

THANKS..!