ANALOG MULTIMETER
MODEL M-1150K
Assembly and Instruction Manual
Elenco Electronics, Inc.
Copyright © 1995 Elenco Electronics, Inc. Revised 1997 REV-D 753012
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PARTS LIST
RESISTORS
QTY SYMBOL VALUE COLOR CODE PART #
r 1R26 .025Ω Shunt Wire 100269
r 1 R12 .96Ω 1% 1/2W black-white-blue-silver-brown 109631
r 1R11 10Ω 1% 1/4W brown-black-black-gold-brown 121030
r 1 R20 18.5Ω 1% 1/4W brown-gray-green-gold-brown 121832
r 1R10 102Ω 1% 1/4W brown-black-red-black-brown 131034
r 1R21 200Ω 1% 1/4W red-black-black-black-brown 132030
r 1 R2 240Ω 1% 1/4W red-yellow-black-black-brown 132430
r 1R18 2KΩ 1% 1/4W red-black-black-brown-brown 142030
r 1R9 3KΩ 1% 1/4W orange-black-black-brown-brown 143033
r 1R3 5KΩ 1% 1/4W green-black-black-brown-brown 145030
r 1 R24 18KΩ 1% 1/4W brown-gray-black-red-brown 151830
r 1 R17 31KΩ 1% 1/4W orange-brown-black-red-brown 153130
r 1 R22 34KΩ 1% 1/4W orange-yellow-black-red-brown 153430
r 1R4 40KΩ 1% 1/4W yellow-black-black-red-brown 154030
r 1 R19 44KΩ 1% 1/4W yellow-yellow-black-red-brown 154430
r 1 R13 83.3KΩ 1% 1/4W gray-orange-orange-red-brown 158330
r 1 R5 150KΩ 1% 1/4W brown-green-black-orange-brown 161533
r 1 R23 195KΩ 1% 1/4W brown-white-green-orange-brown 161930
r 1 R14 360KΩ 1% 1/4W orange-blue-black-orange-brown 163630
r 1R6 800KΩ 1% 1/4W gray-black-black-orange-brown 168030
r 1 R15 1.8MΩ 1% 1/2W brown-gray-black-yellow-brown 171831
r 1R7 4MΩ 1% 1/2W yellow-black-black-yellow-brown 174031
r 1 R16 6.75MΩ 1% 1/2W blue-violet-green-yellow-brown 176731
r 1 R8 15MΩ 1% 1W brown-green-black-green-brown 181532
r 1 R1 680Ω Pot 191311
r 1 R25 10KΩ Pot 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 #
r 1 C2 (470) .047 or .022µF (473) or (223) 244780
Note: C1 is not used
SEMICONDUCTORS
QTY SYMBOL VALUE DESCRIPTION PART #
r 4 D1 - D4 2CZ82P or 1N4148 Diode 314148
MISCELLANEOUS
-1-
QTY DESCRIPTION PART #
r 1 PC Board 510002C
r 1 Fuse 0.5 Amp 533004
r 5 Solder 0.062 551162
r 2 Battery 1.5V AA 590001
r 1 Battery 9V 590009
r 1 Battery Snap 590098
r 1 Battery Contact Double 590094
r 2 Battery Contact Single 590095
r 1 Selector Contact * 610100
r 1 Thumb Wheel Knob 622012
r 1 Selector Knob * 622018
r 1 Top Cover Assembly 623120
r 1 Back cover 623206
r 1 Selector Base * 626015
QTY DESCRIPTION PART #
r 1 Screw 5/8 641573
r 2 Fuse Clip 663060
r 3 Input Socket 664002
r 1 Ball Bearing * 666401
r 1 Selector Spring * 680020
r 1 Manual Assembly 753012
r 1 Grease * 785000
r 2 Wire Bare 3/4 834400
r 1 Wire 1 3/4 834501
r 2 Wire 2 834502
r 1 Wire 3 834503
r 1h
FE Test Lead Set 883300
r 1 Test lead set RWTL1150
* These parts are part of the main rotary switch assembly. This may come preassembled by the factory.
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-2-
CONSTRUCTION
Introduction
Assembly of your M-1150 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.
Soldering
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 - 40 watts is recommended. The tip of the iron must be kept clean at all
times and well tinned. 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 rosin 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 - 100Ω 5% 1/4W Resistor
(brown-black-brown-gold)
Foil Side
þ
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-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.
r Insert 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.
Figure A
680Ω Pot
Figure B
Capacitor C2
0.047 or 0.022µF
Figure C
Diodes have polarity.
Mount them with the
band as shown on the
top legend.
Band
r R1 - 680Ω Pot
(see Figure A)
r D2 - 2CZ82P Diode
(see Figure C)
r R18 - 2KΩ 1% 1/4W Resistor
(red-black-black-brown-brown)
r R24 - 18KΩ 1% 1/4W Resistor
(brown-gray-black-red-brown)
r R19 - 44KΩ 1% 1/4W Resistor
(yellow-yellow-black-red-brown)
r D3 - 2CZ82P Diode
r D4 - 2CZ82P Diode
(see Figure C)
r C2 - .047µF or .022µF Cap.
(473) or (223) (see Figure B)
r
R23 - 195KΩ 1% 1/4W Resistor
(brown-white-green-orange-brown)
r R17 - 31KΩ 1% 1/4W Resistor
(orange-brown-black-red-brown)
r R2 - 240Ω 1% 1/4W Resistor
(red-yellow-black-black-brown)
r R22 - 34KΩ 1% 1/4W Resistor
(orange-yellow-black-red-brown)
r R21 - 200Ω 1% 1/4W Resistor
(red-black-black-black-brown)
r Wire - 2 long
r R20 - 18.5Ω 1% 1/4W Resistor
(brown-gray-green-gold-brown)
r R12 - .96Ω 1% 1/2W Resistor
(black-white-blue-silver-brown)
r R11 - 10Ω 1% 1/4W Resistor
(brown-black-black-gold-brown)
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-4-
Figure 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.
Figure 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
0.5A fuse.
Tabs
r
R14 - 360KΩ 1% 1/4W Resistor
(orange-blue-black-orange-brown)
r
R15 - 1.8MΩ 1% 1/2W Resistor
(brown-gray-black-yellow-brown)
r
R16 - 6.75MΩ 1% 1/2W Resistor
(blue-violet-green-yellow-brown)
r D1 - 2CZ82P Diode
(see Figure C)
r Wire - 2 Long
r R8 - 15MΩ 1% 1W Resistor
(brown-green-black-green-brown)
r R7 - 4MΩ 1% 1/2W Resistor
(yellow-black-black-yellow-brown)
r R6 - 800KΩ 1% 1/4W Resistor
(gray-black-black-orange-brown)
r R5 - 150KΩ 1% 1/4W Resistor
(brown-green-black-orange-brown)
r R3 - 5KΩ 1% 1/4W Resistor
(green-black-black-brown-brown)
r R4 - 40KΩ 1% 1/4W Resistor
(yellow-black-black-red-brown)
r Wire - 1 3/4 long
r Wire - 3 long
r R10 - 102Ω 1% 1/4W Resistor
(brown-black-red-black-brown)
r Fuse Clips / Fuse 0.5A
(see Figure E)
r R9 - 3KΩ 1% 1/4W Resistor
(orange-black-black-brown-brown)
r
R13 - 83.3KΩ 1% 1/4W Resistor
(gray-orange-orange-red-brown)
r Battery Snap
(see Figure F)
r R25 - 10KΩ Pot
(see Figure D)
Note: Make sure that the lead from
D1 doesnt short to R2, B2+ or R13.
Figure D
Mount the 10KΩ pot to the foil side of the PC board as
shown. Solder the leads to the foil side of the PC board.
10kΩ Pot
Foil Side of PC Board
Red or White
Black or Blue
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-5-
ASSEMBLE COMPONENTS TO THE PC BOARD
r Solder the shunt wire into the R26 (.025Ω) 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.
r Bend 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.
Figure 2
Figure 3
ASSEMBLE THE DIAL SELECTOR (Skip if preassembled by the factory.)
r Apply grease along the detent wall as shown in Figure 4.
r Insert the spring into the selector housing and apply a small amount of grease on top of the spring.
r Place a ball bearing on top of the spring and carefully push it down into the housing.
r Holding 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.
r From the front of the case, align the selector knob shaft with the housing shaft and press together.
r Attach 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
r Solder 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).
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INSTALL THE FOLLOWING PARTS
r Install the double battery contact as shown in Figure 5.
r Install 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).
r Install the the two AA batteries in the battery compartment. Be sure to observe the polarity markings on
the bottom of the battery compartment.
r Connect the battery snap to the 9 volt
battery and place the battery in the 9 volt
battery compartment.
r Place the thumb wheel knob onto the 0Ω
ADJ pot located at the lower right of the
meter dial.
r Install the back cover using the 5/8
screw as shown in Figure 6.
Figure 5
Figure 4
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CALIBRATION
Meter Calibration (See Operating and Testing the Multimeter Section for meter operating instructions).
1.
Obtain a voltage source of 0.1V as measured by an accurate voltmeter. The circuit of Figure 7 will work fine.
2. Set the range switch to 0.5VDC.
3. Connect the test leads as shown in Figure 7.
4. Adjust R1 for a reading of 0.1V (10 on 50V scale) on the M-1150 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 250V scale).
Shunt Wire Calibration
To calibrate the shunt wire, you will need a 5A current source like a 5V power supply and a 1Ω 25 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 0.25A/10A position and connect the red and black test leads as
shown in Figure 8. Read the current on the 0-10 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.
Figure 6
Figure 7 Figure 8
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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
51KΩ resistor 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 R10, 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 10 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-
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-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 10, 50 and 250. The 0-10 volt scale
is used for DC voltage ranges of .1, 10 and 1000VDC. The 0-50 volt scale is used for DC voltage ranges of
.5 and 50VDC and the 0-250 volt scale is used for DC voltage ranges of 2.5 and 250VAC. 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 0-250 volt scale is actually 2.5 volts. You should therefore multiply you
reading by .01 (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 0-10, 0-50 and 0-250 scales as used for DC
volts. AC volts may also be read in decibels using the dB scale. The reference voltage (0dB) for the dB
scale is .775 volts. This voltage across 600 ohms dissipates 1mW of power. When dBs are read with the
range switch at 10ACV, the dB scale is read directly. With the range switch at 50ACV add 14dB. With the
range switch at 250ACV add 28dB and at 1000ACV add 40dB.
Ohms are read on the top scale. Multiply the reading by the appropriate factor 1, 10, 1K or 10K 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 0-10 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 150 on the 0-250 scale. Move the decimal point 2 places to the left to obtain 1.5VDC.
4) Set the range switch to 10VDC. The meter should read 1.5 on the 0-10 volt scale.
5) Set the range switch to 50VDC. The meter should move about 1 1/2 small divisions on the 0-50 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 Ω ADJ pot for a zero reading on the ohms (top) scale.
5) Connect the test leads to a known resistor between 1 and 100 ohms and observe the meter reading.
Multiply by the scale factor to obtain the resistance.
6) Set the range switch to X10 and repeat steps 4 and 5 using a 10 to 1K ohm resistor.
7) Set the range switch to X1K and repeat steps 4 and 5 using a 1K to 100K ohm resistor.
8) Set the range switch to X10K and repeat steps 4 and 5 using a 10K to 1M ohm resistor.
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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 120VAC line.
CAUTION: Be very careful when working with 120VAC. Be sure that the range switch is in the 250 or
1000VAC position before connecting the test leads to 120VAC.
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 0.5 amp fuse. Be sure that the test current is below this level.
Obtain a 68KΩ resistor 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 50µ ADC position.
3) Connect the 68KΩ resistor 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 0-50 scale. This converts directly to 22µA.
4) Set the range switch to the 2.5mADC position. Repeat step 3 using a 1KΩ resistor. The meter should
read about 150 on the 0-250 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 10 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 h
FE (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 X10 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 h
FE 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.
Transistor 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 X10 ohms position). For large geranium transistors, set the range switch to
150mA. 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 150mA.
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 150mA scale, move the decimal point one
place to the right.
-10-
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Diode Tests
The diode forward current If and reverse current Ir are 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 150µA, 15mA or 150mA 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
Introduction
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 20,000 ohms per volt. This means that if the
range switch is on the 250V position, the loading to the circuit under test will be 20,000 x 250 = 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 1MΩ resistors 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 10V scale, the input
loading will be about 200KΩ (20,000 ohms/volt times 10V). 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 50V position, the loading will
be 1MΩ and the meter will read 3V. For reasonably accurate measurement, the circuit under test should
have an impedance of less than 100KΩ or you should use the higher ranges. The loading on the 250V and
1000V ranges wil be 5MΩ and 20MΩ respectively, 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 10 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 9KΩ per volt.
On the 250VAC range, the input impedance is therefore 2MΩ.
Figure 9
Figure 10
R9
3K
R35KR4
40KR5150KR6800KR74MR815M
1000
250
50
10
2.5
0.5
0.1
FUSE-COM
R13
83.3K
R14
360K
R15
1.8M
R16
6.75M
1000
250
50
10
FUSE--COM
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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 50mA 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.
Figure 11
Resistance 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, X10 and X1K ranges. On the X10K 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.
Figure 12
-12-
R12
.96
R9
3K
0.25A / 10A
R10
102
FUSE
--COM
25
2.5
R11
10
50µA
DC 10A
.025
Shunt
D4
D3
R20
18.5
R19
44K
FUSE
-COM
X1
External
Resistor
+
R21
200
R22
34K
X1K
X10
3V
X10K
9V
R25
10K
R24
18K
R23
195K
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-13-
hFE
Measurement
Figure 13 shows a simplified diagram of the hFE measuring circuit. Here the range switch is in the X10 ohms
position and the transistor circuit takes the place of the external resistor in the ohms measurement. The
higher the h
FE 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 h
FE of the transistor may be read on the hFE scale.
Figure 13
Specifications
Measurement Ranges Accuracy Remarks
DC Voltage All ranges 3% Input impedance 20KΩ/V
(DCV)
AC Voltage All ranges 5% Input impedance 9KΩ/V
DC Current 50µA-2.5mA-25mA-0.25A 3% Voltage drop:
10A . . . . . . . . . . . . . . . . . 10% 50µA . . . . . . . . . . 100mV
Others . . . . . . . . . 250mV
Resistance All ranges 3% of arc
Size - 6 x 3 7/8 x 1 1/2 inches
Weight - 0.62 pounds
R19
44K
FUSE
--COM
PNP Transistor
+
R21
200
3V
24K
R25
10K
R24
18K
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SCHEMATIC DIAGRAM
-14-
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Elenco Electronics, Inc.
150 W. Carpenter Avenue
Wheeling, IL 60090
(847) 541-3800
http://www.elenco.com
E-mail: elenco@elenco.com
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