Matco Tools MD251 Manuale utente
USER'S MANUAL
MD251 Basic Multimeter
1
1) SAFETY
Terms in this manual
WARNING identifies conditions and actions that could result in serious injury or even death to
the user.
CAUTION identifies conditions and actions that could cause damage or malfunction in the
instrument.
This manual contains information and warnings that must be followed for operating the instrument
safely and maintaining the instrument in a safe operating condition. If the instrument is used in a
manner not specified by the manufacturer, the protection provided by the instrument may be
impaired. The meter is intended only for indoor use.
The meter protection rating, against the users, is double insulation per IEC61010-1 2nd Ed.,
EN61010-1 2nd Ed., UL61010-1 2nd Ed. and CAN/CSA C22.2 No. 61010.1-0.92 to Category II
1000V, CAT III 600V and CAT IV 300V AC & DC.
Terminals (to COM) measurement category:
V : Category II 1000V, CAT III 600V and CAT IV 300V AC & DC.
mAA : Category III 500Vac and 300Vdc.
A : Category III 600Vac and 300Vdc.
Per IEC61010-1 2nd Ed. (2001) Measurement Category
Measurement Category IV (CAT IV) is for measurements performed at the source of the low-
voltage installation. Examples are electricity meters and measurements on primary overcurrent
protection devices and ripple control units.
Measurement Category III (CAT III) is for measurements performed in the building installation.
Examples are measurements on distribution boards, circuit- breakers, wiring, including cables,
bus-bars, junction boxes, switches, socket-outlets in the fixed installation, and equipment for
industrial use and some other equipment, for example, stationary motors with permanent
connection to the fixed installation.
Measurement Category II (CAT II) is for measurements performed on circuits directly connected
to the low voltage installation. Examples are measurements on household appliances, portable
tools and similar equipment.
2
WARNING
To reduce the risk of fire or electric shock, do not expose this product to rain or moisture. To avoid
electrical shock hazard, observe the proper safety precautions when working with voltages above
60 VDC or 30 VAC rms. These voltage levels pose a potential shock hazard to the user. Do not
touch test lead tips or the circuit being tested while power is applied to the circuit being measured.
Keep your fingers behind the finger guards of the test leads during measurement. Inspect test
leads, connectors, and probes for damaged insulation or exposed metal before using the
instrument. If any defects are found, replace them immediately. Do not measure any current that
exceeds the current rating of the protection fuse. Do not attempt a current measurement to any
circuit where the open circuit voltage is above the protection fuse voltage rating. Suspected open
circuit voltage should be checked with voltage functions. Never attempt a voltage measurement
with the test lead inserted into the A/mA or A input jack. Only replace the blown fuse with the
proper rating as specified in this manual. Only use the test lead provided with the equipment or UL
Listed Probe Assembly with rating or better.
CAUTION
Disconnect the test leads from the test points before changing functions. Always set the instrument
to the highest range and work downward for an unknown value when using manual ranging mode.
INTERNATIONAL ELECTRICAL SYMBOLS
!
Caution ! Refer to the explanation in this Manual
Caution ! Risk of electric shock
Earth (Ground)
Double Insulation or Reinforced insulation
Fuse
AC--Alternating Current
DC--Direct Current
2) CENELEC DIRECTIVES
The instruments conform to CENELEC Low-voltage directive 2006/95/EC and Electromagnetic
compatibility directive 2004/108/EC
3
3) PRODUCT DESCRIPTION
Note: Top of the line model is used as representative for illustration purposes. Please refer to your
respective model for function availability.
1) 3-5/6 digits 6000 counts LCD
display
2) Push-buttons for special
functions & features
3) Selector to turn the Power On or
Off and Select a function
4) Input Jack for milli-amp and
micro-amp current functions
5) Input Jack for all functions
EXCEPT current (A, mA, A)
functions
6) Common (Ground reference)
Input Jack for all functions
7) Input Jack for 8A (15A for 30sec)
current function
Analog bar-graph
The analog bar graph provides a visual indication of measurement like a traditional analog meter
needle. It is excellent in detecting faulty contacts, identifying potentiometer clicks, and indicating
signal spikes during adjustments.
JACK
JACK
!
4
Average sensing RMS calibrated
RMS (Root-Mean-Square) is the term used to describe the effective or equivalent DC value of an
AC signal. Most digital multimeters use average sensing RMS calibrated technique to measure
RMS values of AC signals. This technique is to obtain the average value by rectifying and filtering
the AC signal. The average value is then scaled upward (calibrated) to read the RMS value of a
sine wave. In measuring pure sinusoidal waveform, this technique is fast, accurate and cost
effective. In measuring non-sinusoidal waveforms, however, significant errors can be introduced
because of different scaling factors relating average to RMS values.
True RMS
True RMS is a term which identifies a DMM that responds accurately to the effective RMS value
regardless of the waveforms such as: square, sawtooth, triangle, pulse trains, spikes, as well as
distorted waveforms with the presence of harmonics. Harmonics may cause :
1)Overheated transformers, generators and motors to burn out faster than normal
2)Circuit breakers to trip prematurely
3)Fuses to blow
4)Neutrals to overheat due to the triplen harmonics present on the neutral
5)Bus bars and electrical panels to vibrate
Crest Factor
Crest Factor is the ratio of the Crest (instantaneous peak) value to the True RMS value, and is
commonly used to define the dynamic range of a True RMS DMM. A pure sinusoidal waveform has
a Crest Factor of 1.4. A badly distorted sinusoidal waveform normally has a much higher Crest
Factor.
NMRR (Normal Mode Rejection Ratio)
NMRR is the DMM's ability to reject unwanted AC noise effect that can cause inaccurate DC
measurements. NMRR is typically specified in terms of dB (decibel). This series has a NMRR
specification of >60dB at 50 and 60Hz, which means a good ability to reject the effect of AC noise
in DC measurements.
CMRR (Common Mode Rejection Ratio)
Common mode voltage is voltage present on both the COM and VOLTAGE input terminals of a
DMM, with respect to ground. CMRR is the DMM's ability to reject common mode voltage effect
that can cause digit rolling or offset in voltage measurements. This series has a CMRR
specifications of >60dB at DC to 60Hz in ACV function; and >100dB at DC, 50 and 60Hz in DCV
function. If neither NMRR nor CMRR specification is specified, a DMM's performance will be
uncertain.
4) OPERATION
CAUTION
Before and after hazardous voltage measurements, test the voltage function on a known source
such as line voltage to determine proper meter functioning.
5
DCV, ACV, & Line Frequency functions
Press the Hz push-button for one second or more to activate or to exit Hz.
!
DCV
JACK
JACK
ACV
!
JACK
JACK
!
JACK
JACK
Hz
Note:
*Input sensitivity varies automatically with function range selected before activating the Hz function.
6V function range has the highest and the 1000V range has the lowest. It is recommended to first
measure the signal voltage (or current) level then activate the Hz function in that voltage (or
current) range to automatically set the most appropriate trigger level. You can also press the
RANGE button momentarily to select another trigger level manually. If the Hz reading becomes
unstable, select lower sensitivity to avoid electrical noise. If the reading shows zero, select higher
sensitivity.
*Number of Bar-graph pointer is used to indicate input range (sensitivity) selected. 1/2/3/4 pointers
indicate 6/60/600/1000V, 6/10/-/-A, 60/600/-/-mA or 600/6000/-/-uA is selected in corresponding V,
A, mA or uA function respectively. ( “-” means range not available)
*The Hz of mV function is designed specially for logic level (3V or 5V family) frequency
measurement.
6
Resistance, Continuity, Diode test functions
Press the SELECT button momentarily to select the subject functions in sequence. Last selection
will be saved as power up default for repeat measurement convenience.
CAUTION
Discharge capacitors before making any measurement. Large value capacitors should be
discharged through an appropriate resistance load.
CAUTION
Using resistance and continuity function in a live circuit will produce false results and may damage
the instrument. In many cases the suspected component must be disconnected from the circuit to
obtain an accurate reading
Continuity function is convenient for checking wiring connections and operation of switches. A
continuous beep tone indicates a complete wire.
Normal forward voltage drop (forward biased) for a good silicon diode is between 0.400V to
0.900V. A reading higher than that indicates a leaky diode (defective). A zero reading indicates a
shorted diode (defective). An OL indicates an open diode (defective). Reverse the test leads
connections (reverse biased) across the diode. The digital display shows OL if the diode is good.
Any other readings indicate the diode is resistive or shorted (defective).
7
DCmV, ACmV
Press the SELECT button momentarily to select the subject functions in sequence. Last selection
will be saved as power up default for repeat measurement convenience.
A, mA, and A Current functions
Press SELECT button momentarily to toggle between DC and AC.Last selection will be saved as
power up default for repeat measurement convenience.
8
*Note: When measuring a 3-phase system, special attention should be taken to the phase-to-
phase voltage which is significantly higher than the phase-to-earth voltage. To avoid exceeding the
voltage rating of the protection fuse(s) accidentally, always consider the phase-to-phase voltage as
the working voltage for the protection fuse(s).
Electric Field EF-Detection
At Volt or Current function, press the EF button for one second or more and release to toggle to
EF-Detection feature. The meter displays “E.F.” when it is ready. Signal strength is indicated as a
series of bar-graph segments on the display plus variable beep tones.
• Non-Contact EF-Detection: An antenna is located along the top-right end of the meter, which
detects electric field surrounds current-carrying conductors. It is ideal for tracing live wiring
connections, locating wiring breakage and to distinguish between live or earth connections.
• Probe-Contact EF-Detection: For more precise indication of live wires, such as distinguishing
between live and ground connections, use the Red (+) test probe for direct contact measurements.
Hold
The hold feature freezes the display for later view. Press the HOLD button momentarily to toggle
the hold feature.
Relative Zero ( ) mode
Relative zero allows the user to offset the meter consecutive measurements with the displaying
reading as the reference value. Practically all displaying readings can be set as relative reference
value including MAX/MIN feature readings. Press the REL button momentarily to toggle relative
zero mode.
Manual or Auto-ranging
Press the RANGE button momentarily to select manual-ranging, and the meter will remain in the
range it was in, the LCD turns off. Press the button momentarily again to step through the
ranges. Press and hold the button for 1 second or more to resume auto-ranging.
Note: Manual ranging feature is not available in Hz and functions.
9
Set Beeper Off
Press the RANGE button while turning the meter on to temporarily disable the Beeper feature.
Turn the rotary switch OFF and then back on to resume.
Beep-Jack™ Input Warning
The meter beeps as well as displays “InEr” to warn the user against possible damage to the meter
due to improper connections to the A, mA, or A input jacks when other function (like voltage
function) is selected.
Auto-Power-Off (APO)
The Auto-Power-Off (APO) mode turns the meter off automatically to extend battery life after
approximately 34 minutes of no rotary switch or push button operations. To wake up the meter
from APO, press the SELECT, CREST or REC button momentarily or turn the rotary switch OFF
and then back on. Always turn the rotary switch to the OFF position when the meter is not in use
Disabling Auto-Power-Off
Press the SELECT button while turning the meter on to temporarily disable the Auto-Power-Off
(APO) feature. Turn the rotary switch OFF and then back on to resume.
5) MAINTENANCE
WARNING
To avoid electrical shock, disconnect the meter from any circuit, remove the test leads from the
input jacks and turn OFF the meter before opening the case. Do not operate with open case. Install
only the same type of fuse or equivalent
Cleaning and Storage
Periodically wipe the case with a damp cloth and mild detergent; do not use abrasives or solvents.
If the meter is not to be used for periods of longer than 60 days, remove the battery and store it
separately
Trouble Shooting
If the instrument fails to operate, check battery, fuses, leads, etc., and replace as necessary.
Double check operating procedure as described in this user’s manual
If the instrument voltage-resistance input terminal has subjected to high voltage transient (caused
by lightning or switching surge to the system) by accident or abnormal conditions of operation, the
series fusible resistors will be blown off (become high impedance) like fuses to protect the user and
the instrument. Most measuring functions through this terminal will then be open circuit. The series
fusible resistors and the spark gaps should then be replaced by qualified technician.
Indice
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