DMM Aneng V7

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This is a cheap DMM with all common function. It is both manual and auto ranging.

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The box for the meter is designed for both the V7 and V8 meter.

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Inside the box is a pouch with everything in it, except the manual.

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The package included the DMM, a pair of standard probes, the universal probes, a thermocoupler and a manual in addition to the pouch.

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The probes are unbranded and has removable tip covers and is rated for CAT II 1000V and CAT IV 600V

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The plug is shrouded.

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The thermocoupler is designed for insertion into stuff and is with banana plugs.

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The universal probes can be assembled to many different configuration, they are not high quality, but very useful.

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When using the tilting bale it is possible to turn the switch, but not use the buttons with one hand.

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Display

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All the segments on the display.

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Typical screen during usage, show the range.

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In auto mode it will show "Auto" until voltage or resistance is detected.

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Holding down the NCV button will show EF (Electric field) on the display and change to bars when a actual field is detected. The led below the display will flash red and the buzzer will also sound.

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Between the buttons is a led, it can show red, green and "yellow", it is used for NCV, continuity and battery test.



Functions

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Buttons: Rotary switch:
Input

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The terminals fairly retracted into the meter.



Measurements 1uF

A look at the capacitance measurement waveform.

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50Hz frequency output, it goes slightly below zero.

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5000Hz frequency output, it also goes slightly below zero.

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50Hz output loaded with 3700 ohm halved the RMS output voltage, there is a output capacitor that is on the small side.

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5000Hz output with 1220ohm load, again the output is halved, but the curve looks much better.

DMMInputVoltageSweepHz

Frequency input resistance depends on input voltage.

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The mV range has 10Mohm, until the protection clamps, this is measured on the 600mV range, AC and DC is similar.

DMMschema

Voltage input is a bit low in input impedance at 1Mohm in manual range and 280kOhm in AUTO mode, this is basically always Low-Z.
It handled a mix of AC and DC voltage rather well, the AUTO shows the highest or both if they are similar.
It only supports showing frequency in 750VAC range or with the logic input frequency range.



Tear down

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I had to remove four small screws to open the meter.

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And six more screws to remove the circuit board

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The range switch has seven contacts, a lot of encoding must be done to tell the chip what range is selected, a few signals must also be switches.

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The LCD display is screwed and clipped to the circuit board.

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Two more screws and it was loose.

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All parts are on this side. The 600uA shunt (R1: 99ohm) is next to the mA shunt (R22: 1ohm), only the uA shunt is protected by the 5 diodes (D1..D5). I was a bit curious about the 12V test resistor, it must handle 1.5W, it is a larger resistor (R20: 100ohm), 9V load is next (R26: 910ohm) and then 1.5V (R25: 180ohm), they are all placed after the 0.6A fuse, but it will not protect them from overload. The voltage from these resistors goes to a voltage divider (R31 & R12: 1M & 10K), the output goes directly to the main chip.
The input configuration on the V etc. input is a bit special, it has the typical 10Mohm (R4 & R20: 2x5Mohm), a 1Mohm (R9: 1Mohm), a PTC protected (R10: PTC) and a 800kOhm (R32..R35: 4x100kOhm). Both the 10Mohm and 1Mohm is directly connected to the main chip in all position of the range switch, this is the explanation of the input impedance.
The PTC is used together with a transistor pair (Q1 & Q2) in capacitance, 600ohm, frequency, temperature and frequency out. This goes to the main chip through a resistor (R5: 1kOhm).
There is no microprocessor or diode collection in the meter, this means the main multimeter chip is dedicated/programmed for this meter and it must have electronic calibration build in. There is a voltage regulator (U2) and transistors for Buzzer, backlight and flashlight (Q3, Q4 and Q5).
At the top of the circuit board is the NCV antenna.

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Closeup of the top part.

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This side only has pads for the range switch, LCD and buttons. The indicator LED is mounted on the other sides and lights through a hole in the circuit board.

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Conclusion

This is a cheap meter and as usual with cheap meters they do not live up to their CAT rating, 250VAC fuses and maximum 500V in AUTO mode do not match with a 1000V CAT rating. A single 1Mohm resistor to handle the full input voltage is also wrong.
With that said the meter do have a lot of functions and do most of it fairly well, but there are some omissions. I do not see a big reason for a manual range meter, most auto ranging meters can easily be locked in a range when needed. The low input impedance is a huge disadvantage for electronic use, but it can be a advantage for other measurements.



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