DMM UNI-T UT118B

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This is a small pen DMM with voltage, ohms and capacity.

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The meter was in a clamshell pack. On the back is a comparison between the 2 models in this series, only difference is NCV.

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In the pack was the meter, a probe, a screwdriver and a manual in English.

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The probes is standard size and rated for much more than the meter.

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The shroud is standard size.

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And plugs into the back of the meter.

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The tip has a cover that can be locked in retracted position by turning it. There is also a led near the tip to illuminate the area where the measurement is performed, but it is not very bright.

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Display

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The above picture shows all the segments on the display.

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Automatic mode in voltage, it will switch to AC or DC as needed. It is the word "SCAN" that means it is searching for mode.

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Here I have manually selected DC voltage, "SCAN" disappers and "AUTO" means automatic range.

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Automatic scan in ohm, diode, continuity and capacitance mode.

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Manual selection of capacitance.

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NCV or Electric field mode uses display and buzzer to signal that a field is detected.



Functions

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Buttons: Selection of max min will disable auto ranging

Slide switch:

Input

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This meter has the red probe build in, the black probe is connected at the back.


Measurements
1uF

Capacity measurement waveform.

DMMInputVoltageSweepVDC

The specifications says 10Mohm, but that is only at low voltage.

DMMVoltageSweepLowZ

I will rate this input as a LowZ input.

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For good precision on low capacity values, the residual reading must be manually subtracted (There is no REL mode). The meter support capacity ranges at least up to 30mF, but the precision is non-existent in these ranges (Specifications only goes up to 300uF).
The LowZ is not optional see curve with input impedance.



Tear down

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I had to remove 3 screws, before I could open it up.

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There is some mechanical construction around the front and the back to support the inputs.

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Tip retracted and out.

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The circuit board was mounted with clips, the only screw was holding the tip.

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The two wires are for the flashlight in front.

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This side has the connection for the LCD zebra stribe, the backlight (White area), the range switch and four buttons

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At the input there are 3 paths: High impedance (R17 & R17A: 2x5Mohm), low impedance (R33: 100ohm), medium impedance (R21: 100kOhm), the medium impedance has a trimpot in series (ZR3: 5.9kOhm) and a transistor pair for protection (Q5 & Q6), this path is used for input during ohm, diode and capacity. This pair is always connected and keeps the input impedance down at higher voltages. The diodes (D1 & D2) and other parts near ZR2 is the rectifier for the AC ranges.
There is a PTC and a protection pair (PTC, Q3 & Q4) near the multimeter chip, this is for the ohm, diode and capacity ranges.
The multimeter chip (U1: ES51926A 3000 count) is designed for automtic mode selection.

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Conclusion

The meter says CAT II 600V, but the manual says to stay below 300V, I do not believe the rating (CAT II 600 is up to 4000V).

The number of functions in the meter is fairly limited, but it is fast to measure. The (unintentional) Low-Z can be useful for checking mains.



Notes

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