Test/review of DMM UNI-T UT33A+

DMM UNI-T UT33A+

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This is a fairly simple and small DMM, but has a nice selection of ranges.

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The box is for all the UT33 meters with a checkmark for the actual model and a table on the back for comparing the models (in Chinese).
If you want all the function, you must buy all the models, none of them can everything.

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In the box was the meter, probe leads and a instruction sheet in both Chinese and English. The instruction sheet is for all four models in the series (A, B, C, D).

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The standard probes are about normal size, but rating them for 10A is on the optimistic side.

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The plugs are fully shrouded.

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With the meter lying flat it is possible to turn the switch, but on the tilting bale it will slide around.

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Display

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All the segments are shown during power on, not all are used by this meter.

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



Functions

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Buttons:

• Sel/rel: Used to select AC in mV and current ranges and to zero capacity range.
  
• Hold/Backlight: Will freeze the display reading, until pressed again. Hold down to turn backlight on.
  

Rotary switch:

• Off: Meter is turned off
  
• VAC: AC Voltage
  
• VDC: DC Voltage
  
• mV: Milli volt AC and DC, use SEL to select.
  
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  Clik here to view.: Resistance range.
  
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  Clik here to view.: Continuity range.
  
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  Clik here to view.: Diode range.
  
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  Clik here to view.: Capacitance range, use REL to zero before measuring low values.
  
• uA: Micro ampere range, use SEL to select AC.
  
• mA: Milli ampere range, use SEL to select AC.
  
• A: Ampere range, use SEL to select AC.
  

Input

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• 10ADC: 10A DC current input.
  
• COM: The common terminal for all ranges.
  
• xxx: All other ranges, including mA. It is always problematic when a current range shares connector with a voltage range, if the switch is in the wrong position the fuse will blow (at least). This will only affect current, voltage will still work.
  

Measurements

• Volt and frequency
  
  
  
  • 1V AC readings is 5% down at 2.5kHz
    
  • Input impedance is 10-11Mohm on DC and AC
    
  • Input protection is 600V AC/DC
    
  
  
• Current
  
  
  
  • 10A range is fused with a 10A/250V 5×20mm fuse
    
  • mA range is fused with a 0.2A/250V 5×20mm fuse
    
  • 10A range has an audible alarm at 10A or above.
    
  
  
• Ohm, continuity, diode and capacity
  
  
  
  • Ohm needs about 3.5s to measure 100ohm
    
  • Ohm voltage is 1V open and 0.31mA shorted
    
  • Continuity is fast (About 20ms).
    
  • Continuity beeps when resistance is below 31ohm.
    
  • Continuity is 2.1V open and 0.31mA shorted
    
  • Diode range uses 2.2V, max. display is 1.999V at 0.07mA, max. current is 0.9mA shorted
    
  • 2000uF takes about 9 seconds to measure.
    
  • Overload protection is 600V AC/DC
    
  
  
• Miscellaneous
  
  
  
  • Current consumption of meter is 1.2 to 1.6mA (15.5mA with backlight).
    
  • Display gets unstable about 1.6V, but it might show overflow before, battery symbol show at 2.4V.
    
  • Readings will be correct down to 2.4V, below that they can be high or display can show OL
    
  • Backlight works down to 1.6V
    
  • Viewing angle is good, except from the top
    
  • Display updates around 2.5 times/sec
    
  • Backlight will turn off in about 30 seconds.
    
  • Will automatic turn power off in about 15 minutes.
    
  • Standard probes fits in the meter.
    
  • The meter usual need a couple of display update to reach the final value.
    
  • Weight is 208g without accessories, but with sleeve and batteries.
    
  • Size is 135 × 77 × 47mm
    
  
  
• Probes
  
  
  
  • Probe resistance 72mOhm for one, that is fairly high.
    
  • Probe wire is a bit thin, the are 89cm long.
    
  
  

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The meter is a true-rms meter.




Tear down

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I had to remove two screws, the battery cover could stay on.

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The circuit board is shaped to fit the box and uses ceramic fuses.

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I had to remove 3 screws around the range switch to get the circuit board out.

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And four screws to remove the lcd display, the backlight is soldered to the circuit board.

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There is no parts on this side, only pads for switches and lcd display and a marking of where ranges.

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The resistor for the uA range (R7: 99ohm) and uA range (R8: 0.99ohm) is protected by two diodes (D1 & D2: M7). The main input shunt is two resistors (R1 & R2: 2×5Mohm), there is also a secondary input chain (R4 & R5: 2X499kOhm). Ohm output is protected by a PTC (PTC1) and two transistors (Q1 & Q2).
The multimeter IC is a COP (Chip on board) that is bonded directly to the circuit board and then covered with some black stuff.

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Conclusion

The CAT rating do not match the fuses used, i.e. it is not correct, but at least it use fuses and fairly good ones.
The meter has a nice selection of ranges, but is missing frequency and min/max functions for a general purpose meter. This is the best meter in the UT33+ range, but the other meters in the range each has one function this meter is missing (Battery test, temperature, NCV).
I was a bit surprised that this meter is a true rms meter.



Notes

UNI-T do often make rebranded meters, i.e. it may exist with other names on it.

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