Brymen BM251s User manual

USER'S
MANUAL
BM251s
BM252s
BM255s
BM257s

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 IEC/UL/EN61010-1 Ed. 3.0,
IEC/EN61010-2-030 Ed. 1.0, IEC/EN61010-2-033 Ed. 1.0, IEC/UL/EN61010-031 Ed. 1.1 and
CAN/CSA-C22.2 No. 61010-1-12 Ed. 3.0 to Category II 1000V, CAT III 600V and CAT IV 300V AC
& DC.
Terminals (to COM) measurement category:
V / mAA / A :Category II 1000V, CAT III 600V and CAT IV 300V AC & DC.
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.

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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 rated CAT III 1000V 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

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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 10A (20A 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.

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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.
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.

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AutoCheckTM mode (models 257s & 255s only)
This innovative AutoCheckTM feature automatically selects measurement function of DCV, ACV or
Resistance () based on the input via the test leads.
●With no input, the meter displays “Auto” when it is ready.
●With no voltage signal but a resistance below 10M(nominal) is present, the meter displays the
resistance value. When the resistance is below “Audible Threshold”, the meter further gives a
continuity beep tone.
●When a signal above the voltage threshold of 1V DC or AC up to the rated 1000V is present, the
meter displays the voltage value in appropriate DC or AC, whichever larger in peak magnitude.
Note:
*Range-Lock and Function-Lock Feature: When a measurement reading is being displayed in
AutoCheckTM mode, press the RANGE or SELECT button momentarily 1 time can lock the range
or function it was in. Press the button momentarily repeatedly to step through the ranges or
functions.
*As Hazardous-Alert: When making resistance measurements in AutoCheckTM mode, an
unexpected display of voltage readings alerts you that the object under test is being energized.
*Ghost-voltage Buster: Ghost-voltages are unwanted stray signals coupled from adjacent hard
signals, which confuse common multimeter voltage measurements. Our AutoCheckTM mode
provides low (ramp-up) input impedance (approx. 2.5kΩ at low voltage) to drain ghost voltages
leaving mainly hard signal values on meter readings. It is an invaluable feature for precise
indication of hard signals, such as distinguishing between hot and open wires (to ground) in
electrical installation applications.

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WARNING:
AutoCheckTM mode input impedance increases abruptly from initial 2.5kΩ to a few hundred kΩ’s
on high voltage hard signals. “LoZ” displays on the LCD to remind the users of being in such low
impedance mode. Peak initial load current, while probing 1000VAC for example, can be up to
566mA (1000V x 1.414 / 2.5kΩ), decreasing abruptly to approx. 3.8mA (1000V x 1.414 / 375kΩ)
within a fraction of a second. Do not use AutoCheckTM mode on circuits that could be damaged by
such low input impedance. Instead, use rotary selector or high input impedance voltage
modes to minimize loading for such circuits.
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.

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Resistance, Continuity, Capacitance (models 257s, 255s & 252s only), &
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).
DCmV, ACmV, Temperature oC & oF functions (models 257s, 255s & 252s only)
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.

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Note: Be sure to insert the banana plug K-type temperature bead probe Bkp60 with correct
polarities. You can also use a plug adapter Bkb32 (Optional purchase) with banana pins to K-type
socket to adapt other standard K type mini plug temperature probes.
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.

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*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.
PC computer interface capabilities
The instrument equips with an optical isolated interface port at the meter back for data
communication. Press HOLD button while turning the meter on to enable meter PC-COMM output.
Optional purchase PC interface kit BRUA20X is required to connect the meter to the PC computer
RS232 or USB ports.
MAX/MIN at Fast 20/s measurement mode (models 257s & 255s only)
Press REC button momentarily to activate MAX/MIN recording mode. The LCD “MAX MIN” turn
on, and the reading update rate will be increased to 20/second. The meter beeps when new MAX
(maximum) or MIN (minimum) reading is updated. Press the button momentarily to read the MAX
and MIN readings in sequence. Press the button for 1 second or more to exit MAX/MIN recording
mode. Auto-ranging remains, and Auto-Power-Off is disabled automatically in this mode.
5ms CREST capture mode (models 257s & 255s only)