DMM Borbede BD-168B



This is a smaller meter that has a lot of ranges. It exist in a A (Square wave out) and B (Measures temperature) version.





I got the meter in a brown cardboard box, the drawing mostly matches the meter.



It included the DMM, a pair of probes, a thermocoupler and a manual.





The probes is rated for CAT III, but do not include the partial tip covers.



The shrouded plug is the slightly short variety.




A standard cheap thermocoupler.



The range switch is a bit difficult to use single handed when meter is on the tilting bale, it slides around.





















Display



The above picture shows all the segments on the display, the square wave symbol is not used on this meter.



Typical display during usage, it will show the number and what measurement is selected.



The NCV is the usual bars and the buzzer.



Functions



Buttons:

• Select (Yellow): Select the ranges printed with yellow.
• Hold: Freezes the display, hold down for backlight.
• Range/Rel: Will disable auto range and change range, hold down to activate auto range. In capacity mode it will zero the reading.
• Max/min: Starts recording maximum and minimum value, press to select between max/min/disable. Hold down to turn the flashlight on/off.

MAX/MIN will change to manual range and return to auto range when disabled.

Rotary switch:

• Off: Meter is turned off
• VAC: Show AC voltage, using the Select button to select frequency and duty cycle.
• VDC: Show DC voltage.
• : Resistance, diode, continuity, diode and capacitance.
• Hz: Logical frequency and duty cycle (Use Select to change between them).
• A: Current DC and AC (Use Select to change between them).
• mA: Current DC and AC (Use Select to change between them).
• uA: Current DC and AC (Use Select to change between them).
• Temp: Show temperature, use select to change between Fahrenheit and Celsius
• NCV: Non-contact voltage or electric field detection.

Input

• 10A: High current input
• COM: The common terminal for all ranges.
• xxx: All other ranges.

Measurements

• Volt and frequency
  • At 100mVrms in AC voltage frequency range is from 1Hz to 2.1kHz
  • At 2Vrms in AC voltage frequency range is from 1Hz to 60kHz
  • At 1Vrms in frequency input range is from 1Hz to 41MHz
  • At 1Vrms in frequency input the meter can handle a DC offset from -2.5V to +3.1V
  • Duty cycle do not work at 2V input due to the automatic offset compensation, it only shows the correct value shortly when duty cycle as away from 50%.
  • Duty cycle works from 1% to 99% at 100kHz with 4Vpp, precision is within 0.3 (Mostly 0.1).
  • Max/min needs about 150ms to capture a voltage with repeating pulses.
  • 1 VAC is 5% down at 2.3kHz (RMS will not work at the frequency).
  • Input impedance is 10..11Mohm on DC and AC
  • Frequency input is above 1Mohm up to around 1.5 volt, then the protection clamps to 3kOhm
  • Overload protection on DC is 1000VDC and 750VAC peak, except 6V range is 550V DC or AC peak.
  • Overload protection on AC is not rated.
  • Overload protection on frequency is 550VDC and AC peak, but meter may be damage at 250VAC peak (This is what the specifications says).
• Current
  • uAmA current is protected by a 0.63A/250V or 0.6A/250V 5x20mm glass fuse.
  • 10A current is protected by a 10A/250V 5x20mm ceramic fuse.
  • The 10A range has an audible alarm at 10A.
  • Current ranges must only be used up to 36VDC or 25VAC
• Ohm, Continuity, diode and capacitance
  • Ohm needs about 3.0s to measure 100ohm
  • Ohm is 1.1V open and 0.25mA shorted
  • Continuity is fast (About 20ms).
  • Continuity beeps when resistance is below 50ohm.
  • Continuity is 2.1V open and 0.25mA shorted
  • Diode range uses 4.0V, max. display is 3.300V at 0.25mA, max. current is 1.5mA shorted
  • 10uF takes about 2.5 seconds to measure.
  • 11000uF takes about 9.8 seconds to measure.
  • 70000uF takes about 9.8 seconds to measure.
  • Overload protection is 550V DC or AC peak
• Miscellaneous
  • Current consumption of meter is 1.3 to 1.7mA depending on range (Mostly 1.6mA), with backlight it is up to 8.4mA, with both flashlight and backlight it is 13mA.
  • Meter works down to 2.2V where it turns off, battery symbol show at 2.3V.
  • Reading do changes when voltage is down to 2.5V, but it is less than 1% before meter turns off.
  • Backlight and flashlight changes with voltage and works down to the meter turns off.
  • The meter usual shows the correct value on the first display update.
  • Viewing angle is good, except from top.
  • Display updates around 3 times/sec
  • Backlight will automatic turn off in about 12 seconds.
  • Backlight has a hotspot in front of the minus sign.
  • Flashlight can be manually turn on/off and will turn off when the meter turns off.
  • Will automatic turn power off in about 18 minutes.
  • Standard probes cannot be pushed fully down.
  • Weight is 209g without accessories, but with rubber sleeve and batteries.
  • Size is 145 x 70 x 37mm with rubber sleeve.
• Probes
  • Probe resistance 46mOhm for one.
  • Probe wire is soft and 73cm long.

A look at the capacitance measurement waveform.



Frequency input resistance depends on input voltage.



AC voltage may show low voltage when large DC offset is present.



Tear down



There where four screws holding the meter together.





The circuit board is rectangular with most parts on the other side.





Six more screws and the circuit board could be removed.





This side has the fuses, the PTC, the buzzer, the flashlight led and the crystal for the multimeter chip, basically anything that needs some space in height.
The two points marked SW1 & CAL is accessible from the battery compartment without opening the meter.









At the bottom near the input connectors are the current shunts, 0.01ohm wire for 10A, 0.99ohm and 99ohm for mA and uA and a TVS diode for over protection together with the fuse. There is also two MELF resistors for voltage input (2x5Mohm). There is a led (LED3V), probably for some protection and a transistor pair (Q1 & Q2) for protection together with the PTC.
The PTC and transistor clamp is used in all ohm, frequency and temperature selections.
THE NCV antenna is at the top of the circuit board and has a large pull down resistor (R40: 22Mohm).
The multimeter chip must have internal calibration memory, there is no adjustments on the circuit board. It do also include a true RMS converter.







Conclusion

As usual CAT rating is overstated with 250V fuses and a single PTC it will not handle CAT III 1000V or CAT IV 6000V.
The meter is a very cost optimized construction, but it has most of the common function (I am missing mV), even a max/min is included.
It is a nice meter for around the house or hobby usage.



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