DMM Vici VC8145

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This is a fairly cheap bench DMM from a Chinese manufacturer.

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No nice box for the meter was included, probably to save shipping cost (I bought in on Aliexpress).

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It included the DMM, a pair of probes, short leads with alligator clips, a thermocoupler, a usb cable, a mains cable with plug converter, a manual, a screwdriver and a CD.

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The probe is marked CAT III 1000V, but do not have tip covers, i.e. the marking is not correct. The meter is only for CAT II and do not need CAT III probes.

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The plug is fully shrouded with short shroud.

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The thermocoupler is a standard cheap one.

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The short leads with alligator clips is nice for component testing.

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RS232 serial cable, do anybody use these cables anymore?

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This meter uses buttons to select function, but it only have the regular 4 input sockets (Some bench meters have 6).

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The mA fuse is hidden behind the mA socket. It do not follow with the removeable part out.

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The meter has a build in stand that can tilt it a bit.

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On the back is mains connection with voltage adjustment and RS232 connection.






Display

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The above picture shows all the segments on the display.

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

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In temperature mode it will show temperature in Celsius and Fahrenheit

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The dual display can show many different values in the different volt ranges. I have listed them below:


Functions

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Mode buttons:
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Function buttons:


Input

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Measurements 1uF

A look at the capacity measurement waveform.

606.10Hz

Square wave out on default setting.

5.0000kHz

Highest frequency on generator.

5.0000kHz99

With maximum duty cycle, this required 49 presses on a button to get from 50 to 99%, there is no auto repeat or decrement button.

0.5000Hz

Lowest frequency.

606.10Hz3800ohm

The output impedance is about 3.8kohm.

DMMInputVoltageSweepHz

Frequency input resistance.

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The AC range works best up to about 560 volt, then it looses precision according to the specifications.



Software

The software is rather old and the newest Windows it works on is XP V1, a XP simulation on Win10 do not work.
It is possible to find the protocol on the internet for people that want to write their own software.



Tear down

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I had to remove four long screw at the bottom to open the meter, this is also required to replace the A fuse.

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Even though the meter is small for a bench meter, there is a lot of empty space inside.
It looks like the shipping of the meter has been a bit rough (Transformer is tilting).

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The power supply is a 9V DC regulator (IC10: LM7809). A significant part of the power consumption probably goes to the transformer and regulator.
The backplate has printing on both sides.

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The mains switch is also on the power supply. The RS232 interface circuit board is only to connect the cables to the DB9 connector, there is no electronic on it.

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The actual meter is on the front plate with two circuit boards on top of each other. The one at the back is the analog board with all the electronic hidden below a can. The 13A fuse is also here.

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I had to remove 6 screw to get the analog board out, 3 screws was connections to the input terminals, the other 3 was to standoffs in the front plate.

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And five more screws to get the digital section out.

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The front plate with all the buttons and terminals. The hole is for the power switch that is on a rod from the back of the meter.

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The large LCD display that is soldered to the circuit board (No zebra stripe), there is two leds for the backlight (D1 & D2).
Some of the labeling is interesting with AD0..AD3, this must be address/data with only a 4 bit data bus. This is for the ADC. The K signals is for range switching and controls relays.

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The digital board. The large chip is the LCD driver and RS232 data interface (IC5: FSUP01-003), besides it is a microprocessor (IC7: Holtek HT48R30A-1, 8bit 2kx14 program, 96 bytes ram). There is some EEPROM (IC6: Atmel 93C46 128 bytes) probably for calibration.
The RS232 interface is on the simple side, it is two optocouplers (LR & LS: COSMO 1010), because it is isolated power must be supplied by the RS232 handshake signals for the transmitter.
The datasheet for FS970x contains a typical schematic with the FSUP01 chip.

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At the input is a MOV across the voltage input (Very bad idea), there is also a large A shunt (Good idea with a large shunt). The large black round resistor next to the large shunt is a mA shunt and it is protected by D3 and Q16/Q17. The input protection for other ranges is handled by some PTC's (PTC1..PTC4) and some transistor clamps (Q1..Q4).
The analog board has the ADC (IC1: FS9704 80000 count, 4 bit interface with 8 to 24 bit registers), RMS converter (AD737J) and a reference (LM385). There is two probably custom resistors (R4 & R5: Big black boxes). There is two trimpots and two trim capacitors for some calibration.
The range selection is done with 4 relays (K1, K2, K3, K4) and some CMOS switches (IC10 & IC11: HEF4053).
There is some voltage regulation on this board, both 6V (IC3: 70L806) and 5V (IC4: 7805)

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With a microprocessor with only 2k word program memory the amount of functions on this meter is fairly impressive.




Conclusion

There are a lot of details I do not like with the meter: But there is also a lot I like about the meter:
The meter has nearly all the functions you could wish for.



Notes

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