Clarke CDM20 User manual

0607
DIGITAL MULTIMETER
Model No: CDM20
PartNo: 4500007

WARNING
Before attempting to open the case, Always be sure that test leads have been disconnected from
measurement circuits. Close case and tighten screws completely before using the meter to avoid
electrical shock hazard.
DO NOT dispose of this product with general household waste. It must be disposed of according to all laws
governing waste electrical and electronic products at a recognised disposal facility

Thank you for purchasing this CLARKE Digital Multimeter.
Please read this leaflet thoroughly and follow the instructions carefully, in doing so you can look forward to
the multimeter giving you long and satisfactory service.
Guarantee
This CLARKE product is guaranteed against faulty manufacture for a period of 12 months from the date of
purchase. Please keep your receipt as proof of purchase.
This guarantee is invalid if the product is found to have keen abused or tampered with in any way, or not
used for the purpose for which it was intended.
Faulty goods should he returned to their place of purchase. No product can he returned to us without prior
permission. This guarantee does not effect sour statutory rights.
WARNING
Before attempting to open the case, ALWAYS ensure that the test leads have been
disconnected from their measurement circuits. Close the case and tighten the screws
completely before using the meter to avoid the possibility of electric shock
CDM-20 Page-2

CONTENTS PAGE
1. SAFETY INFORMATION ................................................................................................. 1
1.1 PRELIMINARY ................................................................................................................ 1
1.2 DURING USE ................................................................................................................. 2
1.3 SYMBOLS ....................................................................................................................... 3
1.4 MAINTENANCE ............................................................................................................ 4
2. DESCRIPTION ................................................................................................................ 5
3. OPERATING INSTRUCTIONS ......................................................................................... 8
3.1 MEASURINGVOLTAGE ................................................................................................. 8
3.2 MEASURING CURRENT ................................................................................................ 9
3.3 MEASURING RESISTANCE ............................................................................................ 10
3.4 TESTING DIODE ............................................................................................................. 11
3.5 TESTING TRANSISTOR ................................................................................................... 11
CDM-20 Page-3

CDM-20 Page-4
3.6 CONTINUITY TEST .......................................................................................................... 12
4. SPECIFICATIONS ........................................................................................................... 13
4.1 GENERAL ......................................................................................................................13
4.2 DC VOLTAGE ............................................................................................................... 15
4.3 AC VOLTAGE ............................................................................................................... 16
4.4 DC CURRENT ................................................................................................................ 17
4.5 ACCURRENT ................................................................................................................. 18
4.6 RESISTANCE .................................................................................................................. 19
4.7 DIODE AND AUDIBLE CONTINUITY TEST ..................................................................... 20
4.8 TRANSISTOR liFE TEST .................................................................................................... 20
5. ACCESSORIES .............................................................................................................. 21
6. BATTERY & FUSE REPLACEMENT .................................................................................. 21

1. SAFETY PRECAUTIONS
This multimeter has been designed according to lEG-lOb concerning electronic measuring instruments with
an overvoltage category (CAT II) and pollution 2.
Follow all safety and operating instructions to ensure that the meter is used safely and is kept in good
operating condition.
1.1 PRELIMINARY
❉When using this meter, the user must observe all normal safety rules concerning:
• Protection against the dangers of electronic current.
• Protection of the meter against misuse.
❉Full compliance with safety standards can be guaranteed only if used with the test leads supplied. If
necessary, they must be replaced with the same model or same electronic ratings. Measuring leads
must be in good condition. Replacements are available from CLARKE International - see back page.
CDM-20 Page-5

1.2 DURING USE
❉Never exceed the protection limit values indicated in specifications for each range of measurement.
❉When the meter is linked to measurement circuit, do not touch unused terminals.
❉When the value scale to be measured is unknown before hand, set the range selector at the highest
position.
❉Before rotating the range selector to change functions, disconnect test leads from the circuit under
test.
❉Never perform resistance measurements on live circuits.
❉Always be careful when working with voltage above 60V dc or 30V AC rms. Keep fingers behind the
probe barriers while measuring.
❉Before attempting to insert transistors for testing, always be sure that test leads have been
disconnected from any measurement circuits.
❉Components should not be connected to the hFE socket when making voltage measurements with
test leads.
CDM-20 Page-6

1.3 SYMBOLS
Important safety information, refer to the operating manual.
Dangerous voltage may be present.
Earth ground.
Double insulation ( Protection class II).
A Fuse must be replaced with ratings specified in the manual.
1.4 MAINTENANCE
❉Before opening the meter, always disconnect test leads from all sources of electric current.
❉For continue protection against fire, replace fuse only with the specified voltage and current rating:
F 2A1250V (quick acting).
❉If any faults or abnormalities are observed, the meter cannot be used. It must be inspected and
❉repaired by a qualified technician, or returned to CLARKE International for repair.
❉Never use the meter unless the back cover is in place and fastened fully.
❉Do not use abrasives or solvents on the meter, use a damp cloth and mild detergent only. CDM-20 Page-7

2. DESCRIPTION
This meter is a compact, rugged, battery operated,
handheld 3 ½ digit multimeter, capable of
performing the following functions:
• DC and AC voltage measurement
• DC and AC current measurement Resistance
measurement
• Diode measurement
• Audible continuity test
• Transistor hEE measurement
The Dual-slope A/D Convert uses CMOS technology
for auto-Zeroing, polarity selection and overrange
indication. Full overload protection and low battery
indication are provided
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1. Power Switch
2. Display
3. Transistor Testing
Socket
4. Rotary Switch
5. Input Jacks
0.888

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2.1 POWER SWITCH
A push - push switch is used to turn the meter on or off.
2.2 DISPLAY
3 ½ digit, 7 segment, 18mm high LCD.
2.3 FUNCTION AND RANGE SELECTOR
There are different functions and 32 ranges provided. A rotary switch is used to select functions and ranges.
2.4 INPUT JACKS
1. “COM” jack - Plug in connector for black (negative) test lead
2. “V/Ω” jack - Plug in connector for red (positive) test lead for voltage and resistance.
3. “2A” jack - Plug in connector for red test lead for current (2A MAX).
4. “10A” jack - Plug in connector for red test lead for 10A measurement.

CDM-20 Page-10
3. OPERATING INSTRUCTIONS
3.1 MEASURING VOLTAGE
1. Connect the black test lead to the COM jack and the red test lead to the V/Q jack.
2. Set the rotary switch at the desired V or V range position and connect test leads across the source
or load under measurement.
The polarity of the red lead connection will be indicates along with the voltage value when making
DC voltage measurement.
3. When only the figure 1 is displayed, it indicates overrange situation and the higher range has to be
selected
~

CDM-20 Page-11
3.2 MEASURING CURRENT
1. Connect the black test lead to the COM jack and the red test lead to the A jack for a maximum of
2A current For a maximum of 20A, move the red lead to the 10A jack.
2. Set the rotary switch at desired A or A range position and connect test leads in series with the load
under measurement
The polarity of the red lead connection will be indicated along with the current value when making
DC current measurement.
3. When only the figure “1” displayed, it indicates overrange situation and the higher range has to be
selected
~

CDM-20 Page-12
3.3 MEASURING RESISTANCE
1. Connect the black test lead to the COM jack and the red test lead to the V/Ωjack. (The polarity of
red lead is “+” )
2. Set the rotary switch at desired Q position and connect test leads across the resistor under
measurement.
NOTE
1. If the resistance being measured exceeds the maximum value of the range selected or the input is
not connected, an overrange indication “1” will be displayed.
2. When checking in-circuit resistance, be sure the circuit under test has all power removed and that all
capacitors have been fully discharged .
3. For measuring resistances above 1M
Ω the meter may take a few seconds to stabilise. This is normal
for high resistance measurements.

CDM-20 Page-13
3.4 TESTING DIODE
1. Connect the black test lead to the COM jack and the red test lead to the V/Ω jack. (The polarity of
red lead is “+”.
2. Set the rotary switch at the position and connect red lead to the anode, black lead to the
cathode of the diode under testing. The meter will show the approx. forward voltage of the diode. If
the lead connection is reversed, only figure “1” displayed.
3.5 TESTING TRANSISTOR
1. Set the rotary switch at hFE position.
2. Determine whether the transistor to be tested is NPN or PNP type and locate the Emitter, Base and
Collector leads. Insert leads of the transistor into proper holes of the transistor testing socket.
3. The meter will show the approx. hFE value at test condition of base current 10µA and Vce 2.8V.
3.6 CONTINUITY TEST
1. Connect the black test lead to the COM jack and the red test lead to the V/Ωjack. (The polarity of
the red lead is positive “+”
2. Set the rotary switch at position and connect test leads across two points of the circuit under test.
If continuity exists (i.e. resistance less than about 30Ω), built-in buzzer will sound.

CDM-20 Page-14
4.SPECIFICATIONS
Accuracy is specified for a period one year after calibration and at 18º C to 28º C (64º F to 82º F) with
relative humidity to 80 %.
4.1 GENERAL
Maximum Voltage between ............................................... CAT II 1000V.
Teminal and Earth Ground .................................................. CAT III 600V.
Fuse Protection ..................................................................... A: F 2A1250V; 10A: unfused.
Power Supply ........................................................................ 9V battery, Neda 1604 or 6F22.
Display ................................................................................... LCD, 1999 counts, updates 2-3/sec.
Measuring Method ............................................................... Dual-Slope integration ND converter.
Overrange indication .......................................................... “1” figure only on the display.

CDM-20 Page-15
Polarity indication ................................................................ “-” displayed for negative polarity.
Operating Temperature ...................................................... 0ºC to40ºC (32ºF to l04ºF).
Storage Temperature ........................................................... 10ºC to 50ºC (14ºF to 122ºF).
Temp for guaranteed accuracy ........................................ 23ºC ± 5ºC.
Low Battery Indication ......................................................... appears on the display.
Size ( W x L x H) ...................................................................... 88W x 172L x 36H mm.
Weight .................................................................................... 370g (including battery).

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4.2 DC VOLTAGE
Range Accuracy Resolution
200mV 100µV
2V 1mV
20V ± 0.5% of rdg ±1 digits 10mV
200V l00mV
1000V lV
Input Impedance: 10MΩ on all ranges.
Overload Protection: 250 V rms AC for 200mV range, 1000 V peak or 700 V rms AC for other ranges

CDM-20 Page-17
4.3 AC VOLTAGE
Range Accuracy Resolution
200mV ±1.2 % of rdg + 3 digits 100µV
2V 1 mV
20V ±0.8 % of rdg + 3 digits 10mV
200V l00mV
700V ±1.2% of rdg + 3 digits 1V
Input Impedance: 10MΩon all ranges.
Frequency Range: 40Hz to 1 kHz; Indication: Average (rms of sine wave).
Overload Protection: 250V rms AC for 200mV range and 1000V DC or 700V rms AC for other ranges.

CDM-20 Page-18
4.4 DC CURRENT
Range Accuracy Resolution
20µA ± 2.0 % of rdg+ 5 digits 10nA
200µA 0.1µA
2mA ±0.8% of rdg + 1 digits 1µA
20mA 10µA
200mA ± 1.2 % of rdg ± 1 digits 100µA
2A 1mA
10A ±2.0% of rdg + 5 digits l0mA
Max Input Current: 2A:2A. 10A:10A continuous, 20A 15 sec.MAX.
Overload Protection: 2A/250V fuse (10A range unfused); Measuring Voltage Drop: 200mV

CDM-20 Page-19
4.5 AC CURRENT
Range Accuracy Resolution
20µA ±3.0% of rdg + 7digits l0nA
200µA 0 .1µA
2mA ±1.0% of rdg + 3digits 1µA
20mA 10µA
200mA ± 1.8% of rdg 3 digits 100µA
2A 1mA
10A ± 3.0% of rdg + 7 digits l0mA
Max Input Current: 2A2A. 10A10A continuous, .20A 15 sec MAX
Overload Protection: 2A/250V fuse (10A range unfused); Frequency Range 40Hz to 1kHz
Indication: Average (rms of sine wave) Measuring Voltage Drop 200mV