DIGITAL MULTIMETER KIT

DIGITAL MULTIMETER KIT

MODEL M-1006K

Assembly and Instruction Manual

Qty.

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PARTS LIST

If you are a student, and any parts are missing or damaged, please see instructor or bookstore.

If you purchased this meter kit from a distributor, catalog, etc., please contact Elenco Electronics

(address/phone/e-mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.

RESISTORS

(Parts mounted on card.)

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5

1

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Symbol

R9

R8

R7

R13

R6

R5

R17

R12

R14

R4

R15

R3

R25

R10, R11, R24

R2

R18 - R22

R1

R23

Value

.01

Ω

.99

Ω .5% 1/4W

9

Ω .5% 1/4W

100

Ω 5% 1/4W

100

Ω .5% 1/4W

900

Ω .5% 1/4W

910

Ω 1% 1/4W

1k

Ω 5% 1/2W

4.7k

Ω 5% 1/4W

9k

Ω .5% 1/4W

30k

Ω 1% 1/4W

90k

Ω .5% 1/4W

100k

Ω 5% 1/4W

220k

Ω 5% 1/4W

352k

Ω .5% 1/2W

470k

Ω 5% 1/4W

548k

Ω .5% 1/2W

1M

Ω 5% 1/4W

Placed in bag with carded parts.

1 R16 200

Ω (201)

Color Code

Shunt Wire black-white-white-silver-green white-black-black-silver-green brown-black-brown-gold brown-black-black-black-green white-black-black-black-green white-brown-black-black-brown brown-black-brown-gold yellow-violet-red-gold white-black-black-brown-green orange-black-black-red-brown white-black-black-red-green brown-black-yellow-gold red-red-yellow-gold orange-green-red-orange-green yellow-violet-yellow-gold green-yellow-gray-orange-green brown-black-green-gold

Potentiometer

Qty.

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4

1

Symbol

C1

C2, C3, C4, C6

C5

Value

100pF (101)

.1

µF (104)

.1

µF (104)

CAPACITORS

Description

Disc

Mylar (small yellow)

Mylar

Qty.

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Symbol

D1

Value

1N4007

SEMICONDUCTORS

Description

Diode (mounted on resistor card)

191310

Part #

221017

251017S

251017

Part #

314007

Part #

100161

109930

119000

131000

131050

139050

139130

141000

144700

149050

153030

159050

161000

162200

163551

164700

165451

171000

Description

LCD

Zebra

PC Board IC Installed

Fuse 0.2A, 250V

Battery 9V

Battery Snap

Selector Knob

Case Top (Black)

Case Bottom (Black)

Zebra Frame

Screw 2mm x 6mm

MISCELLANEOUS

Part #

351115

500006

516101

533002

590009

590098

622104

623113

623209

629012

643439

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1

6

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3

2

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Description

Screw 2mm x 10mm

Fuse Holder Clips

Socket Transistor

Input Socket

Ball Bearing

Slide Contact

Spring 1/4” (Selector Knob)

Label Front

Grease

Solder Tube

Test Lead Set

Part #

643447

663100

664007

664101

666400

680013

680014

724012

790004

9ST4

RWTL1000B

NOTE:

Not used but printed on PC board: R26 - R29, T1

The 7106 IC1 is already installed on the PC board. This type of installation is called C.O.B. (chip on board). The IC is tested after it is installed on the PC board.

-1-

PARTS IDENTIFICATION

Resistors Battery Snap

Shunt Wire

Selector Knob Potentiometer Fuse

Clip

Slide

Contact

PC Board with IC LCD Assembly

Zebras/LCD/Frame/Cover

Transistor

Test Socket

Zebras

Zebra

Frame

Fuse

LCD

Capacitors

Input Socket

Ball Bearing

Diode

C5

Mylar

Discap

IDENTIFYING RESISTOR VALUES

Use the following information as a guide in properly identifying the value of resistors.

4 Bands

1

2

Multiplier

Tolerance

1 2

5 Bands

3 Multiplier

Tolerance

IDENTIFYING CAPACITOR VALUES

Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or

µF (microfarads). Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in the following manner. The maximum operating voltage may also be printed on the capacitor.

Second Digit Multiplier

Multiplier

For the No.

0

Multiply By 1

1

10

2

100

3

1k

4 5 8

10k 100k .01

9

0.1

First Digit

103K

100V

Tolerance*

Note: The letter “R” may be used at times to signify a decimal point; as in 3R3 = 3.3

Maximum Working Voltage

The value is 10 x 1,000 =

10,000pF or .01

µF 100V

*

The letter M indicates a tolerance of +20%

The letter K indicates a tolerance of +10%

The letter J indicates a tolerance of +5%

METRIC UNITS AND CONVERSIONS

Abbreviation

p n

µ m

– k

M

Means

pico nano micro milli unit kilo mega

Multiply Unit By

.000000000001

.000000001

.000001

.001

1

1,000

1,000,000

Or

10 -12

10 -9

10 -6

10 -3

10 0

10 3

10 6

-2-

1,000 pico units = 1 nano unit

1,000 micro units = 1 milli unit

1,000 units = 1 kilo unit

1,000 nano units = 1 micro unit

1,000 milli units = 1 unit

1,000 kilo units = 1 kilo unit

CONSTRUCTION

Introduction

The most important factor in assembling your M-1006K Digital Multimeter Kit is good soldering techniques.

Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is recommended. The tip of the iron must be kept clean at all times and well tinned.

Safety Procedures

• Wear eye protection when soldering.

• Locate soldering iron in an area where you do not have to go around it or reach over it.

• Do not hold solder in your mouth. Solder contains lead and is a toxic substance. Wash your hands thoroughly after handling solder.

• Be sure that there is adequate ventilation present.

Assemble Components

In all of the following assembly steps, the components must be installed on the top side of the PC board unless otherwise indicated.

The top legend shows where each component goes.

The leads pass through the corresponding holes in the board and are soldered on the foil side.

Use only rosin core solder of 63/37 alloy.

DO NOT USE ACID CORE SOLDER!

What Good Soldering Looks Like

A good solder connection should be bright, shiny, smooth, and uniformly flowed over all surfaces.

1.

Solder all components from the copper foil side only.

Push the soldering iron tip against both the lead and the circuit board foil.

Soldering Iron

Component Lead

Foil

Types of Poor Soldering Connections

1.

Insufficient heat

- the solder will not flow onto the lead as shown.

Rosin

2.

Apply a small amount of solder to the iron tip. This allows the heat to leave the iron and onto the foil.

Immediately apply solder to the opposite side of the connection, away from the iron.

Allow the heated component and the circuit foil to melt the solder.

3.

Allow the solder to flow around the connection.

Then, remove the solder and the iron and let the connection cool.

The solder should have flowed smoothly and not lump around the wire lead.

Solder

Foil

Solder

Foil

4.

Here is what a good solder connection looks like.

Circuit Board

Soldering Iron

Soldering Iron

Soldering iron positioned incorrectly.

2.

Insufficient solder - let the solder flow over the connection until it is covered.

Use just enough solder to cover the connection.

Solder

Component Lead

Gap

3.

Excessive solder - could make connections that you did not intend to between adjacent foil areas or terminals.

Solder

-3-

4.

Solder bridges - occur when solder runs between circuit paths and creates a short circuit. This is usually caused by using too much solder.

To correct this, simply drag your soldering iron across the solder bridge as shown.

Foil

Soldering Iron

Drag

ASSEMBLY INSTRUCTIONS

Identify and install the following parts as shown. After soldering each part, mark a check in the box provided.

Be sure that solder has not bridged to an adjacent pad.

C1 - 100pF (101) Discap

C2 - .1

µF (104) Mylar (small yellow)

R22 - 470k

Ω 5% 1/4W Resistor

(yellow-violet-yellow-gold)

(see Figure A)

R21 - 470k



(see Figure A)

R25 - 100k


(brown-black-yellow-gold)

(see Figure A)

R15 - 30k


(orange-black-black-red-brown)

(see Figure A)

R16 - 200

Ω (201) Potentiometer

(see Figure B)

R17 - 910


(white-brown-black-black-brown)

(see Figure A)

R14 - 4.7k


(yellow-violet-red-gold)

(see Figure A)

R13 - 100


(brown-black-brown-gold)

(see Figure A)

R19 - 470k


R18 - 470k



(see Figure A)

R20 - 470k



(see Figure A)

C5 - .1

µF (104) Mylar

R24 - 220k


(red-red-yellow-gold)

(see Figure A)

C4 - .1


C3 - .1


R23 - 1M


(brown-black-green-gold)

(see Figure A)

R6 - 100

Ω .5% 1/4W Resistor

(brown-black-black-black-green)

(see Figure A)

R5 - 900


(white-black-black-black-green)

(see Figure A)

R4 - 9k


(white-black-black-brown-green)

(see Figure A)

R3 - 90k


(white-black-black-red-green)

(see Figure A)

Figure A Figure B

Stand resistor on end as shown.

Solder and cut off the excess leads.

Mount the potentiometer to the PC board as shown.

-4-

ASSEMBLY INSTRUCTIONS

Identify and install the following parts as shown. After soldering each part, mark a check in the box provided.

Be sure that solder has not bridged to an adjacent pad.

R7 - 9


(white-black-black-silver-green)

R8 - .99


(black-white-white-silver-green)

R12 - 1k


(brown-black-brown-gold)

Figure C

Stand diode on end. Mount with band as shown on the top legend.

C6 - .1


R1 - 548k


(green-yellow-gray-orange-green)

R2 - 352k


(orange-green-red-orange-green)

R11 - 220k



(see Figure A)

R10 - 220k



(see Figure A)

D1 - 1N4007 Diode

(see Figure C)

Band

Install the following parts. Then, mark a check in the box provided.

Insert the narrow end of the three input sockets into the PC board from the solder side, as shown in Figure D.

Solder the sockets to the PC board on the component side only. The solder should extend completely around the socket (see Figure D).

Insert the shunt wire (R9) into the PC board holes from the component side as shown in Figure D. Adjust the wire so that it sticks out the other (solder) side of the PC board 3/16 of an inch. Solder the wire to the

PC board on the component side only.

Be sure that the 8-pin transistor socket will slide easily through its hole in the top case from either direction.

If it does not, carefully slide it through the hole several times in each direction to remove any burrs. Do not push on the socket leads or they may be damaged.

Insert the socket into the PC board holes from the solder side as shown in Figure D.

Be sure that the tab lines up with the hole as shown in the figure. Solder the socket to the PC board on the component side of the PC board as shown in the figure and cut off excess leads.

Feed the battery snap wires up through the holes in the PC board from the solder side as shown in Figure D.

Insert the red wire into the hole marked (9V+) and black wire into hole marked (9V–) as shown. Solder the wires to the PC board.

Insert the two fuse clips into the PC board holes as shown in Figure D. Be sure that the tabs are on the outside as shown in the figure. Solder the clips to the PC board.

-5-

Fuse Clips

Tab

Solder Side

Solder

Shunt Wire

Input Sockets

Battery Snap

Figure D

Zebras

Red Wire

Black Wire

Transistor

Socket

Zebra Frame

Solder Side

Close-up view of the transistor socket and

PC board.

Remove the clear protective film from the front of the LCD (Note:

DO NOT remove the silver backing). Place the LCD, zebra frame, and zebras into the top case as shown in Figure E. Be sure that the LCD tab is in the same direction as shown in the figure.

Cut open the plastic envelope containing the grease and put a small amount of grease in each spring hole of the selector knob as shown in Figure F. Then, insert a 1/4” spring into each hole as shown in the figure.

LCD

Tab

Top Case

Clear Protective Film

1/4” Springs

Spring Holes

Figure E Figure F

-6-

Put the bearings into two opposite indents in the case top as shown in Figure G.

Place the six slide contactors on the selector knobs as shown in Figure G.

Place the selector knob into the case top so that the springs fit over the bearings as shown in Figure G.

Place the PC board over the selector knob. Be sure that the 8-pin socket slides into its hole. Then fasten the PC board with two 6mm screws as shown in Figure G.

Insert the 0.25A, 250V fuse into the fuse clips. Your fuse may be unmarked.

Peel the backing off of the front label and place it on the case top.

Connect a 9V battery to the battery snap.

6mm Screws

PC Board

Figure G

Selector Knob

Rib

Close-up View

Slide Contactor

-7-

Bearings

Battery Compartment

Case Top

TESTING, CALIBRATION, AND TROUBLESHOOTING

TESTING OF LCD

With no test leads connected to the meter, move the selector switch around the dial. You should obtain the following readings. A (–) sign may also be present or blinking.

1) ACV Range: 750

200

2) DCA,10A Ranges: 200

µ

2000

µ

20m

200m

10A

0 0.0

0 0 0

0 0.0

0 0 0

0.0 0

0 0.0

0.0 0

3) Ohms, Diode and h

FE

Ranges: B indicates blank.

h

FE

0 0 0

Diode ( )

200

1 B B B

1 B B.B

2000

20k

200k

2000k

1 B B B

1 B.B B

1 B B.B

1 B B B

4) DCV Range: 200m

2000m

20

200

1000

0 0.0

0 0 0

0.0 0

0 0.0

0 0 0

If any of these tests fail: a) Check that the battery is good.

b) Check the values of resistors R14, R15, R19, R20, R23 - R25.

c) Check the values of capacitors C1 - C6.

d) Check the PC board for solder bridges and bad solder connections.

e) Check that the slide contactors are seated correctly.

f ) Check that the LCD and zebras are seated correctly.

CALIBRATION

Refer to the METER OPERATION section for test lead connections and measurement procedure.

A/D CONVERTER CALIBRATION

Turn the range selector switch to the 20V position and connect the test leads. Using another meter of known accuracy, measure a DC voltage of less than 20 volts (such as a 9V battery). Calibrate the kit meter by measuring the same voltage and adjusting R16 until the kit meter reads the same as the accurate meter (do not use the kit meter to measure its own battery). When the two meters agree, the kit meter is calibrated. Turn the knob to the OFF position and remove the voltage source.

SHUNT WIRE CALIBRATION

To calibrate the shunt wire, you will need a 5 amp current source such as a

5V power supply and a 1 ohm, 25 watt resistor. If a 5 amp source is not available, you can use a lower current (2 amps). If no supply is available, it is not important to do this test. Set the range switch to the 10A position and connect the test leads as shown in Figure H. If the meter reads higher than

5A, resolder the shunt wire so that there is less wire between the 10A DC and

COM sockets.

If the meter reads low, resolder the shunt wire so that there is more wire between the sockets.

123

10A DC

V

ΩmA

COM

Power Supply

+

5VDC

–

1

Ω

25 Watts

Figure H

If the calibration fails: a) Check the PC board for solder bridges and bad solder connections.

b) Check the value of resistors R7 - R9, R23, and capacitor C3.

-8-

DC VOLTS TEST

1) If you have a variable power supply, set the supply to about the midpoint of each of the DCV ranges and compare the kit meter reading to a meter known accuracy.

2) If you do not have a variable power supply, make the following two tests: a) Set the range switch to 2000mV and measure the voltage across the 100 ohm resistor of Figure Ia. You should get about 820mV. Compare the reading to a meter of known accuracy.

b) Set the range switch to 200mV and measure the voltage across the 100 ohm resistor of Figure Ib. You should get about 90mV. Compare the reading to a meter of known accuracy.

If any of these tests fail:

123 123 a) Recheck the meter calibration.

b) Check the value and the soldering of resistors R1-

R6, R12-R17, R21-R24, and capacitor C3.

9V

1k

Ω

10A DC

V

ΩmA

COM

9V

10k

Ω

10A DC

V

ΩmA

COM

100

Ω

100

Ω

Figure Ia Figure Ib

AC VOLTS TEST

To test the ACV ranges, we will need a source of AC voltage. The AC power line is the most convenient.

CAUTION: Be very careful when working with 120VAC. Be sure that the range switch is in the 200 or 750VAC position before connecting the test leads to 120VAC.

1) Set the range to 200VAC and measure the AC power line. The voltage should be about 120VAC. Compare the reading to a meter of known accuracy.

2) Set the range to 750VAC and measure the AC power line. The voltage should be about 120VAC. Compare the reading to a meter of known accuracy.

If either if the above tests fail: a) Check the values and the soldering of resistors R1 - R6, R22.

b) Check that diode D1 is mounted as shown in the assembly instructions.

DC AMPS TEST

1) Set the range switch to 200

µA and connect the meter as in Figure J. With R

A equal to 100k

Ω the current should be about 90

µA. Compare the reading to a known accurate meter.

2) Set the range switch and R

A as in the following table. Read the currents shown and compare to a known accurate meter.

123

Range Switch

2000

µA

20mA

200mA

R

A

10k

Ω

1k

Ω

470

Ω

Current (approx.)

900

µA

9mA

19mA

R

A

9V

10A DC

V

ΩmA

COM

Accurate

Meter

If any of the above tests fail: a) Check the fuse.

b) Check the value and soldering of resistors R7, R8, and R9.

Figure J

-9-

RESISTANCE/DIODE TEST

1) Measure a resistor of about half of the full scale value of each resistance range. Compare the kit meter readings to those from a meter of known accuracy.

2) Measure the voltage drop of a good silicon diode. You should read about 700mV. Power diodes and the base to emitter junction of power transistors may read less.

If any of these tests fail: a) Check the values and the soldering of resistors R1 - R6, and R12.

h

FE

1) Set the range switch to h

FE transistor socket.

and insert a small transistor into the appropriate NPN or PNP holes in the

2) Read the h

FE of the transistor. The h reading between 100 and 300.

FE of transistors varies over a wide range, but you will probably get a

If this check fails: a) Check that the transistor socket is aligned according to Figure D.

b) Check the value and soldering of resistors R10, R11, and R29.

FINAL ASSEMBLY

Snap the case bottom onto the case top and fasten with the two 10mm screws as shown in Figure K.

Screws

Case

Bottom

Figure K

Battery

Case Top

-10-

THEORY OF OPERATION

A block diagram of the M-1006K is shown in Figure 1. Operation centers around a custom LSI chip. This chip contains a dual slope A/D (analog to digital) converter, display latches, seven segment decoder and display drivers. A block diagram of the IC functions is shown in Figure 2. The input voltage or current signals are conditioned by the selector switches to produce an output DC voltage with a magnitude between 0 and 199mV.

If the input signal is 100VDC, it is reduced to 100mVDC by selecting a 1000:1 divider. Should the input be

100VAC, it is first rectified and then divided down to 100mVDC. If current is to be read, it is converted to a DC voltage by internal shunt resistors.

V

AC

Converter

V

Voltage

Divider

V

DC

Analog

Data

A/D

Converter

& Display

Driver

Input

Selector

Switches

Ohms

Converter

Ω

Selector

Switches

Current

Shunt

I

Decimal

Point

Display

Figure 1

For resistance measurements, an internal voltage source drives the test resistor in series with a known resistor.

The ratio of the test resistor voltage to the known resistor voltage is used to determine the value of the test resistor.

The input of the 7106 IC is fed to an A/D converter. Here the DC voltage is changed to a digital format. The resulting signals are processed in the decoders to light the appropriate LCD segments.

Timing for the overall operation of the A/D converter is derived from an external oscillator whose frequency is selected to be 25kHz. In the IC, this frequency is divided by four before it clocks the decade counters. It is then further divided to form the three convert-cycles phases. The final readout is clocked at about two readings per second.

The digitized measurements are presented to the display as four decoded digits (seven segments) plus polarity.

The decimal point position on the display is determined by the selector switch setting.

A/D CONVERTER

A simplified circuit diagram of the analog portion of the A/D converter is shown in Figure 3. Each of the switches shown represent analog gates which are operated by the digital section of the A/D converter. The basic timing for switch operation is keyed by the external oscillator. The conversion process is continuously repeated. A complete cycle is shown in Figure 3.

Any given measurement cycle performed by the A/D converter can be divided into three consecutive time periods, autozero (AZ), integrate (INTEG) and read. A counter determines the length of the time periods. The integrate period is fixed at 1,000 clock pulses. The read period is a variable time that is proportional to the unknown input voltage. It can vary from zero counts for zero input voltage to 2,000 counts for a full scale input voltage. The autozero period varies from 1,000 to 3,000 counts. For an input voltage less than full scale autozero gets the unused portion of the read period. The value of the voltage is determined by counting the number of clock pulses that occur during the read period.

During autozero a ground reference is applied as an input to the A/D converter. Under ideal conditions, the output of the comparator would also go to zero. However, input-offset-voltage errors accumulate in the amplifier loop and appear at the comparator output as an error voltage. This error is impressed across the AZ capacitor where it is stored for the remainder of the measurement cycle. The stored level is used to provide offset voltage correction during the integrate and read periods.

-11-

The integrate period begins at the end of the autozero period. As the period begins, the AZ switch opens and the INTEG switch closes. This applies the unknown input voltage to the input of the A/D converter. The voltage is buffered and passed on to the integrator to determine the charge rate (slope) on the INTEG capacitor At the end of the fixed integrate period, the capacitor is charged to a level proportional to the unknown input voltage.

During the read period, this voltage is translated to a digital indication by discharging the capacitor at a fixed rate and counting the number of clock pulses that occur before it returns to the original autozero level.

As the read period begins, the INTEG switch opens and the read switch closes. This applies a known reference voltage to the input to the A/D converter. The polarity of this voltage is automatically selected to be opposite that of the unknown input voltage, thus causing the INTEG capacitor to discharge at a fixed rate (slope). This rate is determined by the known reference voltage. When the charge is equal to the initial starting point

(autozero level), the read period is ended. Since the discharge slope is fixed during the read period, the time required for discharge is proportional to the unknown input voltage. Specifically, the digital reading displayed is

1000 (V

IN

/ V

REF

).

The autozero period and thus a new measurement cycle begins at the end of the read period. At the same time the counter is released for operation by transferring its contents (the previous measurement value) to a series of latches. This stored data is then decoded and buffered before being used to drive the LCD display.

-12-

Figure 2

7106 IC Functions

b a e f d g a b c

28

BACKPLANE

TYPICAL SEGMENT OUTPUT

V+

0.5mA

Segment

Output

2mA

Internal Digital Ground

* Three inverters.

One inverter shown for clarity.

LCD PHASE DRIVER

7 Segment

Decode

7 Segment

Decode

7 Segment

Decode

LATCH

Thousand Hundreds Tens Units

200

*

To Switch Drivers

From Comparator Output

CLOCK

OSC 1

7

OSC 2

6

OSC 3

4

-4

LOGIC CONTROL

Internal Digital Ground

1V

V+

6.2V

500

Ω

3

TEST

8

V

DIGITAL SECTION

IN HI

39

C

V+

REF

+

10

µA

INT

REF HI

42 44

A-Z &

Z1

C

REF

REF LO C

REF

43

41

BUFFER

36

R

INT

V+

1

A-Z &

Z1

+

2.8V

Z1

DE (-) DE (+)

6.2V

37

C

AZ

AUTO

ZERO

INTEGRATOR

C

INT

35

INT

+

A-Z

+

COMPARATOR

A-Z

+

DE (+)

DE (-)

ZERO

CROSSING

DETECTOR

POLARITY

FLIP/FLOP

TO

DIGITAL

SECTION

ANALOG SECTION of 7106

COMMON

40

IN LO

38

INT

A-Z & DE(+)

& Z1

V

34

+ REF

(Flying

Capacitor)

Read AZ

To

Digital

Control

Logic

Integ.

Integ.

Unknown

Input

Voltage +

AZ

Figure 3

Counter Output

AZ

0

Integ.

Read

160ms

+.20

.15

.10

.05

0

1000

0 500 1000 1500

DUAL SLOPE A/D CONVERTER

2000

AZ

-13-

DC VOLTAGE MEASUREMENT

Figure 4 shows a simplified diagram of the DC voltage measurement function. The input voltage divider resistors add up to 1 megaohm. Each step down divides the voltage by a factor of ten. The divider output must be within the range –0.199 to +0.199 volts or the overload indicator will function. The overload indication consists of a 1 in the most significant digit and blanks in the remaining digits.

Volts

200mV

900k

Ω

2V

90k

Ω

20V

9k

Ω

200V

900

Ω

1kV

100

Ω

Low Pass

Filter

100mV

REF

7106

Common

Figure 4

Simplified DC Voltage Measurement Diagram

AC VOLTAGE MEASUREMENT

Figure 5 shows a simplified diagram of the AC voltage measurement function. The AC voltage is first rectified and passed through a low pass filter to smooth out the waveform. A scaler reduces the voltage to the DC value required to give the correct RMS reading.

Volts

Rectifier

Low Pass

Filter - Scaler

Low Pass

Filter

100mV

REF

7106

200V

900

Ω

750V

100

Ω

Common

Figure 5

Simplified AC Voltage Measurement Diagram

CURRENT MEASUREMENT

Figure 6 shows a simplified diagram of the current measurement function. Internal shunt resistors convert the current to between –0.199 to +0.199 volts which is then processed in the 7106 IC to light the appropriate LCD segments. When current in the range of 10A is to be read, it is fed to the 10A input and does not pass through the selector switch.

A

10A

200

µA

2000

µA

900

Ω

20mA

200mA

9

Ω

10A

.99

Ω

.01

Ω

100

Ω

2000

µA

200

20mA

200mA

10A

µA

Low Pass

Filter

100mV

REF

7106

Common

Figure 6

Simplified DC Amps Measurement Diagram

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RESISTANCE MEASUREMENT

Figure 7 shows a simplified diagram of the resistance measurement function. A simple series circuit is formed by the voltage source, a reference resistor from the voltage divider (selected by the selector switches), and the test (unknown) resistor. The ratio of the two resistors is equal to the ratio of their respective voltage drops. Therefore, since the value of one resistor is known, the value of the second can be determined by using the voltage drop across the known resistor as a reference. This determination is made directly by the A/D converter.

Ω

Test

Resistor

100

Ω

900

Ω

9k

Ω

2000

Ω/Dio

20k

Ω

90k

Ω

200k

Ω

Common

900k

Ω

200

Ω

2000k

Ω

Voltage

Source

Low Pass

Filter

Reference

Voltage

7106

Overall operation of the A/D converter during a resistance measurement is basically as described earlier with one exception. The reference voltage present during a voltage measurement is replaced by the voltage drop across the reference resistor. This allows the voltage across the unknown resistor to be read during the read period.

Figure 7

Simplified Resistance Measurement Diagram

h

FE

MEASUREMENT

Figure 8 shows a simplified diagram of the h

FE measurement function.

Internal circuits in the 7106 IC maintain the COMMON line at 2.8 volts below V+. When a PNP transistor is plugged into the transistor socket, base to emitter current flows through resistor R10. The voltage drop in resistor R10 due to the collector current is fed to the 7106 and indicates the h

FE of the transistor. For an NPN transistor, the emitter current through R11 indicates the h

FE of the transistor.

R10

220k

Ω

PNP

E

V+

B

C

NPN

C

B

R11

220k

Ω

Low Pass

Filter

100mV

Ref.

E

R23

10

Ω

Common

Figure 8

7106

SPECIFICATIONS

GENERAL

DISPLAY

OVERRANGE INDICATION

MAXIMUM COMMON MODE

VOLTAGE

STORAGE ENVIRONMENT

3 1/2 digit LCD, with polarity

3 least significant digits blanked.

500V peak.

–15 O C to 50 O C.

TEMPERATURE COEFFICIENT (0 O C to 18 O C and 28 O C to 50 O C) less than 0.1 x applicable accuracy specification per O C.

POWER

DIMENSIONS

9V alkaline or carbon zinc battery.

128 x 75 x 24mm.

DC VOLTAGE

RANGE

200mV

2000mV

20V

200V

1000V

RESOLUTION

0.1mV

1mV

10mV

100mV

1V

MAXIMUM ALLOWABLE INPUT

INPUT IMPEDANCE

ACCURACY

+0.5% rdg + 2d

+0.5% rdg + 2d

+0.5% rdg + 2d

+0.5% rdg + 2d

+0.5% rdg + 2d

1000VDC or peak AC.

1M

Ω.

DIODE CHECK

RANGE

DIODE

TRANSISTOR h

FE

TEST

RANGE

NPN/PNP

RESOLUTION

1mV

TEST RANGE

0 - 1000

DC CURRENT

RANGE

200

µA

2000

µA

20mA

200mA

10A

RESOLUTION

0.1

µA

1

µA

10

µA

100

µA

10mA

OVERLOAD PROTECTION

ACCURACY

+1% rdg + 2d

+1% rdg + 2d

+1% rdg + 2d

+1.2% rdg + 2d

+2% rdg + 3d

.25A/250V fuse (mA input only).

AC VOLTAGE

RANGE

200V

750V

RESOLUTION

100mV

1V

MAXIMUM ALLOWABLE INPUT

FREQUENCY

RESISTANCE

RANGE

200

Ω

2000

Ω

20k

Ω

200k

Ω

2000k

Ω

RESOLUTION

0.1

Ω

1

Ω

10

Ω

100

Ω

1k

Ω

MAXIMUM OPEN CIRCUIT VOLTAGE

750Vrms.

45 - 450Hz.

ACCURACY

+1.2% rdg + 10d

+1.2% rdg + 10d

2.8V.

ACCURACY

+0.8% rdg + 2d

+0.8% rdg + 2d

+0.8% rdg + 2d

+0.8% rdg + 2d

+1% rdg + 2d

MAX TEST CURRENT

1.4mA

TEST CURRENT

Ib = 10

µA

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MAX OPEN CIRCUIT VOLTAGE

2.8V

TEST VOLTAGE

Vce 3V

METER OPERATION

PRECAUTIONS AND PREPARATIONS FOR MEASUREMENT

1) Be sure the battery is connected to the battery snap and correctly placed in the battery compartment.

2) Before connecting the test leads to the circuit, be sure the range switch is set to the correct position.

3) Be sure that the test leads are connected to the correct meter terminals before connecting them to the circuit.

4) Before changing the range switch, remove one of the test leads from the circuit.

5) Operate the instrument only in temperatures between 0 and 50 O C and in less than 80% RH.

6) Pay careful attention to the maximum rated voltage of each range and terminal.

7) When finished making measurements, set the switch to OFF. Remove the battery when the instrument will not be used for a long period of time.

8) Do not use or store the instrument in direct sunlight or at high temperature or humidity.

VOLTAGE MEASUREMENTS

1) Connect the black test lead to the “COM” terminal.

2) Connect the red test lead to the “V

ΩMA” terminal.

3) Set the range switch to the desired “V ” or “V~” position. If the magnitude of the voltage is not known, set the switch to the highest range.

4) Connect the leads across the points to be measured and read the display. If the range switch is too high, reduce it until a satisfactory reading is obtained.

DCA MEASUREMENTS

HIGH CURRENTS (200mA to 10A)


2) Connect the red test lead to the 10ADC terminal.

3) Set the range switch to the 10A position.

4) Open the circuit to be measured and connect the leads in series with the load to be measured.

5) Read the display. If the display read less than 200mA, follow the low current procedure below.

6) Turn off all of the power to the circuit being tested and discharge all of the capacitors before disconnecting the test leads.

LOW CURRENTS (less than 200mA)


8) Connect the red test lead to the V

ΩMA terminal.

9) Set the range switch to the desired A position. If the magnitude of the current is not known, set the switch to the highest position.

10) Open the circuit to be measured and connect the leads in series with the load to be measured.

11) Read the display. If the range switch is too high, reduce it until a satisfactory reading is obtained.

12) Turn off all power to the circuit being tested and discharge all capacitors before disconnecting the test leads.

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RESISTANCE MEASUREMENTS



ΩMA” terminal.

3) Set the range switch to the desired “

Ω” position.

4) If the resistance being measured is connected to a circuit, turn off the power to the circuit being tested and discharge all of the capacitors.

5) Connect the leads across the resistor to be measured and read the display.

When measuring high resistance, be sure not to contact adjacent points even if insulated. Some insulators have relatively low resistance and will cause the measured resistance to be lower than the actual resistance.

DIODE CHECK



ΩMA” terminal.

3) If the diode being measured is connected to a circuit, turn off all power to the circuit and discharge all capacitors.

4) Set the range switch to “ ”.

Forward Voltage Check

5) Connect the red lead to the anode and the black lead to the cathode of the diode. Normally the forward voltage drop of a good silicon diode reads between 450 and 900mV.

Reverse Voltage Check

6) Reverse the leads to the diode. If the diode is good, an overrange indication is given (a 1 in the most significant digit and blanks in the remaining digits). If the diode is bad, “000” or some other value is displayed.

h

FE

MEASUREMENTS

1) Set the range switch to h

FE and insert the test transistor into the appropriate NPN or PNP holes in the transistor socket.

2) Read the h

FE of the transistor.

BATTERY & FUSE REPLACEMENT

To replace battery and fuse (250mA/250V), remove the 2 screws in the bottom of the case.

Simply remove the old fuse/battery and replace with a new fuse/battery.

QUIZ

1. The function of the A/D converter is to . . .

A) convert digital to analog.

B) divide the analog signal by 2.

C) convert analog to digital.

D) convert AC to DC.

2. The divider used for DC voltage measurements is a . . .

A) divide by 20.

B) capacitance divider.

C) divide by 5.

D) resistor divider.

3. When the AC voltage is measured, it is first . . .

A) divided by 2.

B) rectified.

C) divided by 100.

D) sent to a high pass filter.

4. When measuring current, the shunt resistors convert the current to . . .

A) –0.199 to +0.199 volts.

B) –1.199 to +1.199 volts.

C) –0.099 to +0.099 volts.

D) –199 to +199 volts.

5. The DC voltage divider resistors add up to . . .

A) 100

Ω.

B) 1000

Ω.

C) 100k

Ω.

D) 1M

Ω.

B

A,

B, 10.

B, 4.

C, 9.

D, 3.

, 8.

, 2.

A, 7.B

1.C

s:

, 6.

Answer

5.D

6. Resistance measurements are made by . . .

A) comparing voltage drops in the unknown resistor and a reference resistor.

B) measuring the current in the unknown resistor.

C) measuring the current in the reference resistor.

D) equalizing the voltage drops in the unknown and the reference resistors.

7. The measurement cycle performed by the A/D converter can be divided into time periods known as . . .

A) long and short.

B) autozero, integrate and read.

C) zero, read and interphase.

D) convert, integrate and display.

8. A resistor with the band colors green-black-green-brown-green is . . .

A) 50.5k

Ω +5%.

B) 5.15k

Ω +10%.

C) 5.05k

Ω +.5%.

D) 5.05k

Ω +1%.

9. The M-1005K has . . .

A) A 3 digit display.

B) A 3 1/2 digit display.

C) A 4 1/2 digit display.

D) None of the above.

10.When measuring 450mA, the meter leads should be connected to . . .

A) COM and V

ΩmA.

B) COM and 10A.

C) 10A and V

ΩmA.

D) COM and Building GND.

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SCHEMATIC DIAGRAM

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