Elenco Electronics M-1150K User guide

ANALOG MULTIMETER
MODEL M-1150K
Assembly and Instruct on Manual
Elenco Electron cs, Inc.
Copyright © 1995 Elenco Electronics, Inc. Revised 1997 REV-D 753 12

PARTS LIST
RESISTORS
QTY SYMBOL VALUE COLOR CODE PART #
r1R26 .25ΩShunt Wire 1 269
r1 R12 .96Ω1% 1/2W black-white-blue-silver-brown 1 9631
r1R11 1Ω1% 1/4W brown-black-black-gold-brown 121 3
r1 R2 18.5Ω1% 1/4W brown-gray-green-gold-brown 121832
r1R1 12Ω1% 1/4W brown-black-red-black-brown 131 34
r1R21 2Ω1% 1/4W red-black-black-black-brown 132 3
r1 R2 24 Ω1% 1/4W red-yellow-black-black-brown 13243
r1R18 2KΩ1% 1/4W red-black-black-brown-brown 142 3
r1R9 3KΩ1% 1/4W orange-black-black-brown-brown 143 33
r1R3 5KΩ1% 1/4W green-black-black-brown-brown 145 3
r1 R24 18KΩ1% 1/4W brown-gray-black-red-brown 15183
r1 R17 31KΩ1% 1/4W orange-brown-black-red-brown 15313
r1 R22 34KΩ1% 1/4W orange-yellow-black-red-brown 15343
r1R4 4KΩ1% 1/4W yellow-black-black-red-brown 154 3
r1 R19 44KΩ1% 1/4W yellow-yellow-black-red-brown 15443
r1 R13 83.3KΩ1% 1/4W gray-orange-orange-red-brown 15833
r1 R5 15 KΩ1% 1/4W brown-green-black-orange-brown 161533
r1 R23 195KΩ1% 1/4W brown-white-green-orange-brown 16193
r1 R14 36 KΩ1% 1/4W orange-blue-black-orange-brown 16363
r1R6 8KΩ1% 1/4W gray-black-black-orange-brown 168 3
r1 R15 1.8MΩ1% 1/2W brown-gray-black-yellow-brown 171831
r1R7 4MΩ1% 1/2W yellow-black-black-yellow-brown 174 31
r1 R16 6.75MΩ1% 1/2W blue-violet-green-yellow-brown 176731
r1 R8 15MΩ1% 1W brown-green-black-green-brown 181532
r1 R1 68 ΩPot 191311
r1 R25 1 KΩPot 191515
* NOTE: All fixed resistors are 1% tolerance (last stripe, brown). In some cases, resistors with a .5% tol-
erance (last stripe, green) may be used in place of the 1% resistors. Please ignore the tolerances printed
on the resistor card.
CAPACITORS
QTY SYMBOL VALUE MARKING PART #
r1 C2 (47 ) . 47 or . 22µF (473) or (223) 24478
Note: C1 is not used
SEMICONDUCTORS
QTY SYMBOL VALUE DESCRIPTION PART #
r4 D1 - D4 2CZ82P or 1N4148 Diode 314148
MISCELLANEOUS
-1-
QTY DESCRIPTION PART #
r1 PC Board 51 2C
r1 Fuse .5 Amp 533 4
r5 Solder . 62 551162
r2 Battery 1.5V AA 59 1
r1 Battery 9V 59 9
r1 Battery Snap 59 98
r1 Battery Contact Double 59 94
r2 Battery Contact Single 59 95
r1 Selector Contact * 61 1
r1 Thumb Wheel Knob 622 12
r1 Selector Knob * 622 18
r1 Top Cover Assembly 62312
r1 Back cover 6232 6
r1 Selector Base * 626 15
QTY DESCRIPTION PART #
r1 Screw 5/8 641573
r2 Fuse Clip 663 6
r3 Input Socket 664 2
r1 Ball Bearing * 6664 1
r1 Selector Spring * 68 2
r1 Manual Assembly 753 12
r1 Grease * 785
r2 Wire Bare 3/4 8344
r1 Wire 1 3/4 8345 1
r2 Wire 2 8345 2
r1 Wire 3 8345 3
r1h
FE Test Lead Set 8833
r1 Test lead set RWTL115
* These parts are part of the ma n rotary sw tch assembly. Th s may come preassembled by the factory.

-2-
CONSTRUCTION
Introduct on
Assembly of your M-115 Analog Multimeter Kit will prove to be an exciting project and give you much satisfaction and personal
achievement. If you have experience in soldering and wiring techniques, then you should have no problem with the assembly
of this kit. Care must be given to identifying the proper components and in good soldering habits. Above all, take your time
and follow these easy step-by-step instructions. Remember, An ounce of prevention is worth a pound of cure. Avoid making
mistakes and no problems will occur.
CAUTION: WEAR SAFETY GLASSES WHEN ASSEMBLING THIS KIT.
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 and the board is turned to solder the
component leads on the foil side. Solder immediately unless the pad is adjacent to another hole which will interfere with the placement
of the other component. Cut excessive leads with a diagonal cutter. Then, place a check mark in the box provided next to each step to
indicate that the step is completed. Be sure to save the extra leads for use as jumper wires if needed.
Solder ng
The most important factor in assembling your multimeter is good soldering techniques. Using the proper soldering iron is of prime
importance. A small pencil type soldering iron of 25 - 4 watts is recommended. The t p of the ron must be kept clean at all
t mes and well t nned. Many areas on the PC board are close together and care must be given not to form solder shorts. Size
and care of the tip will eliminate problems.
For a good soldering job, the areas being soldered must be heated sufficiently so that the solder flows freely. Apply the solder
simultaneously to the component lead and the component pad on the PC board so that good solder flow will occur. Be sure that
the lead extends through the solder smoothly indicating a good solder joint. Use only ros n core solder of 60/40 alloy. DO NOT
USE ACID CORE SOLDER! Do not blob the solder over the lead because this can result in a cold solder joint.
1. Solder all components from
the copper foil side only.
Push the soldering iron tip
against both the lead and
the circuit board foil.
Component Lead
Soldering Iron
Circuit Board
Foil
2. First 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 com-
ponent and the circuit foil to
melt the solder.
Solder
Soldering Iron
Foil
Example 1
Poor solder connections occur
when the lead is not heated
sufficiently. The solder will not
flow onto the lead as shown. To
correct. reheat the connection
and, if necessary, apply a small
amount of additional solder to
obtain a good connection.
Solder does not flow onto the
lead. A hard rosin bead sur-
rounds and insulates the con-
nection.
Poor solder
connection
Mount Part
Soldering iron posi-
tioned incorrectly.
Example 2
A solder bridge occurs when
solder runs between circuit
paths and creates a short cir-
cuit. This is usually caused
by using too much solder. To
correct this, simply drag your
soldering iron across the sol-
der bridge as shown.
4. Here is what a good sol-
der connection looks like.
Cut off excess leads.
3. Allow the solder to flow
around the connection.
Then, remove the solder
and the iron and let the con-
nection cool. The solder
should have flowed
smoothly and not lump
around the wire lead.
Solder Soldering Iron
Foil
Bend Leads to Hold Part Solder and Cut Off Leads
Rx - 1 Ω5% 1/4W Resistor
(brown-black-brown-gold)
Foil Side
þ

-3-
ASSEMBLE COMPONENTS TO THE PC BOARD
After each step, put a check in the box located next to the step that you have completed.
rInsert the three input sockets into the PC board holes as shown in Figure 1. Note that there is a lip on
one end of the input socket. The lip should rest on the legend side of the PC board. Solder the input
sockets to the PC board as shown in Figure 1. Apply enough heat to allow the solder to flow around the
input socket.
F gure A
68 ΩPot
F gure B
Capacitor C2
. 47 or . 22µF
F gure C
Diodes have polarity.
Mount them with the
band as shown on the
top legend.
Band
rR1 - 68 ΩPot
(see Figure A)
rD2 - 2CZ82P Diode
(see Figure C)
rR18 - 2KΩ1% 1/4W Resistor
(red-black-black-brown-brown)
rR24 - 18KΩ1% 1/4W Resistor
(brown-gray-black-red-brown)
rR19 - 44KΩ1% 1/4W Resistor
(yellow-yellow-black-red-brown)
rD3 - 2CZ82P Diode
rD4 - 2CZ82P Diode
(see Figure C)
rC2 - . 47µF or . 22µF Cap.
(473) or (223) (see Figure B)
r
R23 - 195KΩ1% 1/4W Resistor
(brown-white-green-orange-brown)
rR17 - 31KΩ1% 1/4W Resistor
(orange-brown-black-red-brown)
rR2 - 24 Ω1% 1/4W Resistor
(red-yellow-black-black-brown)
rR22 - 34KΩ1% 1/4W Resistor
(orange-yellow-black-red-brown)
rR21 - 2 Ω1% 1/4W Resistor
(red-black-black-black-brown)
rWire - 2 long
rR2 - 18.5Ω1% 1/4W Resistor
(brown-gray-green-gold-brown)
rR12 - .96Ω1% 1/2W Resistor
(black-white-blue-silver-brown)
rR11 - 1 Ω1% 1/4W Resistor
(brown-black-black-gold-brown)

-4-
F gure F
Battery snap - Insert red or white wire
through the hole marked B2+ and black or
blue wire through hole marked B2--. Then
solder wires to PC board.
F gure E
Insert fuse clips through the
PC board. Be sure tabs are
positioned as shown below.
Solder clips to PC board. Be
sure to heat clips thoroughly
when soldering. Install the
.5A fuse.
Tabs
r R14 - 36 KΩ1% 1/4W Resistor
(orange-blue-black-orange-brown)
r R15 - 1.8MΩ1% 1/2W Resistor
(brown-gray-black-yellow-brown)
r R16 - 6.75MΩ1% 1/2W Resistor
(blue-violet-green-yellow-brown)
rD1 - 2CZ82P Diode
(see Figure C)
rWire - 2 Long
rR8 - 15MΩ1% 1W Resistor
(brown-green-black-green-brown)
rR7 - 4MΩ1% 1/2W Resistor
(yellow-black-black-yellow-brown)
rR6 - 8 KΩ1% 1/4W Resistor
(gray-black-black-orange-brown)
rR5 - 15 KΩ1% 1/4W Resistor
(brown-green-black-orange-brown)
rR3 - 5KΩ1% 1/4W Resistor
(green-black-black-brown-brown)
rR4 - 4 KΩ1% 1/4W Resistor
(yellow-black-black-red-brown)
rWire - 1 3/4 long
rWire - 3 long
rR1 - 1 2Ω1% 1/4W Resistor
(brown-black-red-black-brown)
rFuse Clips / Fuse .5A
(see Figure E)
rR9 - 3KΩ1% 1/4W Resistor
(orange-black-black-brown-brown)
r R13 - 83.3KΩ1% 1/4W Resistor
(gray-orange-orange-red-brown)
rBattery Snap
(see Figure F)
rR25 - 1 KΩPot
(see Figure D)
Note: Make sure that the lead from
D1 doesnt short to R2, B2+ or R13.
F gure D
Mount the 1 KΩpot to the foil side of the PC board as
shown. Solder the leads to the foil side of the PC board.
1 kΩPot
Foil Side of PC Board
Red or White
Black or Blue

-5-
ASSEMBLE COMPONENTS TO THE PC BOARD
rSolder the shunt wire into the R26 (. 25Ω) position on the PC board as shown in Figure 2. The leads should extend
approximately 1/16 out of the bottom (solder side) of the PC board.
rBend the two 3/4 bare
wires as shown. Insert
one wire into the B1+
and -- slots on the PC
board. Bend the lead
over so it lays flat on
the copper pad. Solder
the two leads to the
copper pad as shown.
F gure 2
F gure 3
ASSEMBLE THE DIAL SELECTOR (Sk p f preassembled by the factory.)
rApply grease along the detent wall as shown in Figure 4.
rInsert the spring into the selector housing and apply a small amount of grease on top of the spring.
rPlace a ball bearing on top of the spring and carefully push it down into the housing.
rHolding the bearing in place, insert the housing into the case as shown in Figure 4. Keep holding the housing in
place of the ball bearing will come out.
rFrom the front of the case, align the selector knob shaft with the housing shaft and press together.
rAttach the selector contact to the selector housing by first inserting the tab on the contact into the notch on the
housing. Then, lay the contact on the housing as shown in Figure 4.
M+
M--
SOLDER METER MOVEMENT WIRES TO PC BOARD
rSolder the black wire from the meter movement to the hole marked M-- on the PC board (see Figure 3).
r
Solder the red wire from the meter movement to the solder pad marked M+ on the legend side of the PC board
(see Figure 3).

-6-
INSTALL THE FOLLOWING PARTS
rInstall the double battery contact as shown in Figure 5.
rInstall the two single battery contacts as shown in Figure 5. Solder the bare wires from B1 to the battery
contacts (as shown in Figure 5).
rInstall the the two AA batteries in the battery compartment. Be sure to observe the polarity markings on
the bottom of the battery compartment.
rConnect the battery snap to the 9 volt
battery and place the battery in the 9 volt
battery compartment.
rPlace the thumb wheel knob onto the Ω
ADJ pot located at the lower right of the
meter dial.
rInstall the back cover using the 5/8
screw as shown in Figure 6.
F gure 5
F gure 4

-7-
CALIBRATION
Meter Cal brat on (See Operating and Testing the Multimeter Section for meter operating instructions).
1.
Obtain a voltage source of .1V as measured by an accurate voltmeter. The circuit of Figure 7 will work fine.
2. Set the range switch to .5VDC.
3. Connect the test leads as shown in Figure 7.
4. Adjust R1 for a reading of .1V (1 on 5 V scale) on the M-115 meter.
If a DC power supply or an accurate voltmeter is not available, then use a fresh 1.5V battery and adjust R1
to read 1.55V on the 2.5V scale (155 on 25 V scale).
Shunt W re Cal brat on
To calibrate the shunt wire, you will need a 5A current source like a 5V power supply and a 1Ω25 watt resis-
tor. If a 5A source is not available, you can use a lower current (2A). If no supply is available, it is not impor-
tant to do this test. Set the range switch to .25A/1 A position and connect the red and black test leads as
shown in Figure 8. Read the current on the -1 scale immediately below the meter mirror. If the meter
reads high, resolder the shunt wire so that there is less between the two mounting holes. If the meter reads
low, resolder the shunt wire so that there is more wire between the mounting holes.
F gure 6
F gure 7 F gure 8

TROUBLESHOOTING CHART
This chart lists the condition and possible causes of several malfunctions. If a particular part is mentioned
as a possible cause, check that part to see if it was installed correctly. Also, check that part and the parts
connected to it for good solder connections.
PROBLEM POSSIBLE CAUSE
No DC voltage reading 1. Check for open fuse.
Refer to Figure 7 for a better understanding 2.
Check resistors R2 through R9 for correct values and
of how the meter works. good solder connections.
3. Check that the PC board is seated properly and that
the three board clamps are engaged.
4. Check D3 and D4 for shorts.
5. Check R1 for an open connection.
6. Check the meter movement. Unsolder the red wire
from the meter movement to the PC board. Place a
51KΩresistor between the red wire and the positive
side of a 1.5V battery. Connect the negative side of
the battery to the black wire from the meter move-
ment. The meter should read a little over half scale.
Wrong meter readings 1. Check resistors R24, R25 and R2 through R9 for cor-
rect values and good solder connections.
No AC voltage reading 1. Check for open fuse.
Refer to Figure 8 for a better understanding 2. Check diodes D1 through D4 for opens and shorts.
of how the meter works. 3. Check resistors R13 through R16 and capacitor C1
for correct values and good solder connections.
No DC current reading 1. Check for open fuse.
Refer to Figure 9 for a better understanding 2. Check resistors R1 , R11, R12 and R26 for correct
of how the meter works. values and good solder connections.
Ohms 1. If meter cannot be zeroed:
Refer to Figure 1 for a better understanding A. Check for open fuse.
of how the meter works. B.
Check for weak or improperly installed batteries.
C. Check that the battery snap and battery con-
tacts are installed correctly.
D. Check resistors R19 through R25 for correct
value and good solder connections.
2. If meter does not read correctly:
A. Check R19 through R25 for correct value and
good solder connections.
No hFE reading 1. See Ohms above.
Refer to Figure 11 for a better understanding 2. Check that the test leads are in the correct socket
of how the meter works. for the type of transistor being tested.
-8-

-9-
OPERATING AND TESTING THE MULTIMETER
CAUTION: When measuring an unknown voltage or current, always start with the range switch set to the
highest scale. Then, if necessary, move the range switch down until the meter reads in the middle or right
half of the dial.
Checking your multimeter for proper operation is fairly easy. Of prime importance is knowing which scale
is read for each setting of the range switch. DC voltage is read on the dial immediately below the meter
mirror. This dial is marked with three scales with full scale readings of 1 , 5 and 25 . The -1 volt scale
is used for DC voltage ranges of .1, 1 and 1 VDC. The -5 volt scale is used for DC voltage ranges of
.5 and 5 VDC and the -25 volt scale is used for DC voltage ranges of 2.5 and 25 VAC. The readings taken
on these scales must be multiplied by the proper scale factor. For example, when the range switch is in
2.5VDC, a full scale reading on the -25 volt scale is actually 2.5 volts. You should therefore multiply you
reading by . 1 (move the decimal point 2 places to the left). DCmA are read using the same three scales
as DC volts.
AC volts are read on the red dial marked ACV using the same -1 , -5 and -25 scales as used for DC
volts. AC volts may also be read in decibels using the dB scale. The reference voltage ( dB) for the dB
scale is .775 volts. This voltage across 6 ohms dissipates 1mW of power. When dBs are read with the
range switch at 1 ACV, the dB scale is read directly. With the range switch at 5 ACV add 14dB. With the
range switch at 25 ACV add 28dB and at 1 ACV add 4 dB.
Ohms are read on the top scale. Multiply the reading by the appropriate factor 1, 1 , 1K or 1 K as indicat-
ed by the range switch.
If you are new to reading analog meter scales, assemble and try the Dial Scale Reading Exercise included
with this kit.
Before starting tests, set the meter needle to zero . The zero adjust screw is located on the meter face next
to the base of the needle. With no test leads connected, slowly turn this screw until the needle points to
zero on the -1 scale immediately below the meter mirror. We will now test each meter function. If the
meter should fail to perform as indicated, refer to the troubleshooting section for assistance.
DC Voltage Test
1) Plug the red test lead into the positive (+) socket, and the black lead into the --COM socket.
2) Set the range switch to 2.5VDC.
3) Connect the red lead to the positive side of a 1.5V battery (you may remove and use one of the 1.5V bat-
teries from the meter). Connect the black lead to the negative side of the battery. The meter should
read about 15 on the -25 scale. Move the decimal point 2 places to the left to obtain 1.5VDC.
4) Set the range switch to 1 VDC. The meter should read 1.5 on the -1 volt scale.
5) Set the range switch to 5 VDC. The meter should move about 1 1/2 small divisions on the -5 volt
scale.
Ohms Test
CAUTION: When measuring ohms, be sure that there is no voltage across the circuit being tested.
1) Plug the red test lead into the positive (+) socket, and the black lead into the --COM socket.
2) If you removed the 1.5 volt battery from the multimeter for the DC voltage test, replace it now.
3) Set the range selector switch to X1.
4) Short the test leads together and adjust the ΩADJ pot for a zero reading on the ohms (top) scale.
5) Connect the test leads to a known resistor between 1 and 1 ohms and observe the meter reading.
Multiply by the scale factor to obtain the resistance.
6) Set the range switch to X1 and repeat steps 4 and 5 using a 1 to 1K ohm resistor.
7) Set the range switch to X1K and repeat steps 4 and 5 using a 1K to 1 K ohm resistor.
8) Set the range switch to X1 K and repeat steps 4 and 5 using a 1 K to 1M ohm resistor.

AC Voltage Test
In reading AC voltage, it is necessary to obtain a known source of AC. A 12 volt transformer is preferred.
If one is not available, use the 12 VAC line.
CAUTION: Be very careful when working with 12 VAC. Be sure that the range switch is in the 25 or
1 VAC position before connecting the test leads to 12 VAC.
1) Plug the red test lead into the + socket, and the black lead into the -COM socket.
2) Set the range switch to the appropriate ACV position. Touch the test leads to the power source and
observe the meter reading. Then, multiply by the appropriate scale factor.
DC Current Test
The DC current circuit is protected by a .5 amp fuse. Be sure that the test current is below this level.
Obtain a 68KΩresistor and a 1.5 volt battery (you may again use one of the 1.5V meter batteries).
Proceed as follows:
1) Plug the red test lead into the + socket and the black lead into the -COM socket.
2) Set the range switch to the 5 µADC position.
3) Connect the 68KΩresistor to the positive side of the battery. Connect the red test lead to the other side
of the resistor. Connect the black test lead to the negative side of the battery. The meter should read
about 22 on the -5 scale. This converts directly to 22µA.
4) Set the range switch to the 2.5mADC position. Repeat step 3 using a 1KΩresistor. The meter should
read about 15 on the -25 scale. Move the decimal point two places to the left to obtain 1.5mADC.
5) Check the remaining scales using a power supply and suitable resistors.
6) See Calibration Section for 1 amp range.
hFE Test
The hFE of a transistor is read using the two small test leads. One is a single lead with a single black alli-
gator clip and the other is a double lead with two wires, one with a red and the other with a black alligator
clip. There is a 24KΩresistor in series with the black wire on the double test lead. To measure the hFE (beta)
of an NPN transistor, proceed as follows.
1) Plug the double test lead into the --COM socket and the single test lead into the + socket.
2) If you removed the 1.5 volt battery from the multimeter, replace it now.
3) Set the range switch to the ohms X1 position.
4) Connect the single test lead to the red wire of the double test lead and adjust the ΩADJ pot for a zero
reading on the ohms scale.
5) Connect the single test lead to the emitter of the transistor.
6) Connect the red lead of the double test lead to the collector and the black lead to the base of the tran-
sistor.
7) Read the hFE of the transistor on the blue hFE scale immediately below the red ACV scale.
8) To measure a PNP transistor, connect the transistor to the test leads in the same way, but reverse the
test leads at the meter. That is, plug the single lead into the -COM socket and the double lead into the
+ socket.
Trans stor Leakage Current Test
Leakage current is read on the Iceo scale. For small geranium transistors, set the range switch to 15mA
(the blue marking under the X1 ohms position). For large geranium transistors, set the range switch to
15 mA. For silicon transistors, the leakage is usually too small to read. Read the leakage current as fol-
lows:
1) Plug the red test lead into the + socket and the black lead into the --COM socket.
2) Set the range switch to 15mA or 15 mA.
3) Short the test leads together and adjust the ΩADJ pot for a zero reading on the ohms (top) scale.
4) For an NPN transistor, connect the red test leads to the emitter and the black test lead to the collector.
For PNP transistors, connect the red test lead to the collector and the black lead to the emitter.
5) Read the leakage current on the Iceo scale. If you are on the 15 mA scale, move the decimal point one
place to the right.
-10-

-11-
D ode Tests
The diode forward current Ifand reverse current Irare read LI scale. To check a diode in the forward direc-
tion proceed as follows:
1) Plug the red test lead into the + socket and the black lead into the --COM socket.
2) Select the approximate forward current desired 15 µA, 15mA or 15 mA and set the range switch to this
position (blue markings in ohms range).
3) Short the test leads together and adjust the ΩADJ pot for a zero reading on the ohms (top) scale.
4) Connect the red test lead to the cathode (striped end) of the diode and the black test lead to the anode
of the diode.
5) Read the forward current on the LI scale. The voltage drop across the diode is shown on the LV scale
immediately below the LI scale.
THEORY OF OPERATION
Introduct on
Your multimeter is of professional quality using 1% precision resistors throughout the design. The accura-
cy at full scale reading will be within 3% of full scale DC voltage or current and 5% of full scale AC voltage.
The accuracy of the ohms measurement is 3% of arc.
On the DC volts range, the loading impedance of the meter is 2 , ohms per volt. This means that if the
range switch is on the 25 V position, the loading to the circuit under test will be 2 , x 25 = 5MΩ.
The input loading of the meter is a very important factor to be considered when measuring the voltage of a
high resistance circuit. Take the example where two 1MΩresistors are connected in series across a 9V bat-
tery. The voltage at the junction of the resistors will be 4.5V. When measured on the 1 V scale, the input
loading will be about 2 KΩ(2 , ohms/volt times 1 V). The voltage at the junction will therefore drop
to 1.28V and the meter will read this voltage. If the meter is switched to the 5 V position, the loading will
be 1MΩand the meter will read 3V. For reasonably accurate measurement, the circuit under test should
have an impedance of less than 1 KΩor you should use the higher ranges. The loading on the 25 V and
1 V ranges wil be 5MΩand 2 MΩrespectively, but it will be hard to read 4.5V on these ranges.
DC Voltage Measurement
Figure 9 shows a simplified diagram of the DC voltage measuring circuit. Here resistors are switched in
series with the meter to provide the desired ranges.
AC Voltage Measurement
Figure 1 shows a simplified diagram of the AC voltage measuring circuit. Two diodes are added to the
series resistors to rectify the AC voltage. The input impedance on the AC voltage ranges is 9KΩper volt.
On the 25 VAC range, the input impedance is therefore 2MΩ.
F gure 9
F gure 10
R9
3K
R3
5K
R4
4 K
R5
15 K
R6
8 K
R7
4M
R8
15M
1
25
5
1
2.5
.5
.1
FUSE-COM
R13
83.3K
R14
36 K
R15
1.8M
R16
6.75M
1
25
5
1
FUSE--COM

DC Current Measurement
Figure 11 shows a simplified diagram of the DC current measuring circuit. Here the resistors are placed
across the meter to shunt the current. On the 5 mA range, the current is fed directly to the meter and the
voltage drop across the meter at full scale deflection is .1 volt. On all of the other ranges, the full scale volt-
age drop across the meter is .25 volts. A .5 amp fuse and special diodes are added to the circuit for pro-
tection against overload.
F gure 11
Res stance Measurement
Figure 12 shows a simplified diagram of the resistance measuring circuit. Here a known 1% resistor, in par-
allel with the meter and the zero adjust resistors, is compared to the external resistor in a series circuit. The
current is supplied by the 3V battery on the X1, X1 and X1K ranges. On the X1 K range, a 9V battery is
placed in series with the 3V battery to supply more current to the series circuit. To calibrate the ohms cir-
cuit, the external resistor is made zero ohms by shorting the test leads together. This places the full battery
voltage across the internal resistors. The current in the meter is adjusted to full scale deflection, or zero
reading on the dial. When an external resistor is made equal to the internal resistance, the meter will deflect
to half scale and the dial marking will show its value.
F gure 12
-12-
R12
.96
R9
3K
.25A / 1 A
R1
1 2
FUSE
--COM
25
2.5
R11
1
5 µA
DC 1 A
. 25
Shunt
D4 D3
R2
18.5
R19
44K
FUSE
-COM
X1
External
Resistor
+
R21
2
R22
34K
X1K
X1
3V
X1 K
9V
R25
1 K
R24
18K
R23
195K

-13-
hFE Measurement
Figure 13 shows a simplified diagram of the hFE measuring circuit. Here the range switch is in the X1 ohms
position and the transistor circuit takes the place of the external resistor in the ohms measurement. The
higher the hFE of the transistor, the more current flows in the external circuit and the lower the effective resis-
tance. The meter reads this resistance and the hFE of the transistor may be read on the hFE scale.
F gure 13
Spec f cat ons
Measurement Ranges Accuracy Remarks
DC Voltage All ranges 3% Input impedance 2 KΩ/V
(DCV)
AC Voltage All ranges 5% Input impedance 9KΩ/V
DC Current 5 µA-2.5mA-25mA- .25A 3% Voltage drop:
1 A . . . . . . . . . . . . . . . . . 1 % 5 µA . . . . . . . . . . 1 mV
Others . . . . . . . . . 25 mV
Resistance All ranges 3% of arc
Size - 6 x 3 7/8 x 1 1/2 inches
Weight - .62 pounds
R19
44K
FUSE
--COM
PNP Transistor
+
R21
2
3V
24K
R25
1 K
R24
18K

SCHEMATIC DIAGRAM
-14-

Elenco Electron cs, Inc.
15 W. Carpenter Avenue
Wheeling, IL 6 9
(847) 541-38
http://www.elenco.com
E-mail: [email protected]