DMM Hioki DT4282

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Hioki is a Japanese test equipment manufacturer, this multimeter is one of their top models.

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I got it in a cardboard box designed for the two top models, they can be compared on the back of the box. It also list what is in the box and some accessories.

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The box contained the meter, batteries, test probes and a manual in Japanese (A English manual can be downloaded). No thermocoupler or pouch.
The manual is very thorough with functions and specifications.

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The probes has removable tip covers, the tip and tip cover has the usual CAT markings.

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The shrouded plug is full size.

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The range switch is fairly easy to turn and with this heavy meter it is stable both lying and standing. Due to the shutters plugs in the terminals can block the movement of the range switch.

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The meter has a couple of power on options (hold button down and turn on), some of them are saved (nice). To help remembering them the tilting bale has a list on the back.

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The computer interface is a small brick with a usb connector that is placed in this hole. The adapter is a bit expensive.
The serial number label can also be seen, this serial number was on the box and is coded into the meter and can be electronically read from the meter.

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Display

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The above picture shows all the segments on the display, these are not shown on a normal power on, but using a power on option (VA PEAK), they can be shown.
The current clamp symbol is not used on this model.

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

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In AC ranges the frequency is shown on the secondary display.

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Some function will also use the secondary display.

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The memory uses its own counter on the display.
Secondary display functions (After / is small display):

Functions

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Buttons: Rotary switch:

Input

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Measurements 1uF

A look at the capacity measurement waveform.

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The input resistance in mVDC

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Some AC ranges works down to 20Hz, but with lower precision.
The meter has a input impedance of 1Mohm in AC, this is nearly a permanent Low-Z (They are usual 0.3Mohm or lower).



Tear down


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Six screws and the back could be removed, two of them are under the battery cover. It is necessary to remove one of the fuses to get the back cover up.

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The battery box is part of the back cover with spring connections to the circuit board. There is also lenses for the opto communication.

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I did not really get to see much, there is a secondary cover.

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I only had to remove one screw to remove it (This screw holds all the internal covers), but there are more internal covers.
The internal cover is conductive plastic, pressing two probes into it gives about 600-1000ohm at any distance.

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Removing the screws on the terminals allowed my to take the circuit board out.

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The other side of the circuit board also has internal covers.

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But they are loose now.

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The display was mounted with two screws and the backlight was soldered to the circuit board.

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The backside of the backlight is shielded and it has 3 connections (red + white led and common).

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The circuit board and all the internal covers are one unit and can be removed when unscrewed from the terminals (This image is from when I put it together again).

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The current input do not use the common 10A wire shunt, but a regular smd resistor (R26: 0.01ohm), the mA (R27: 1ohm) and uA (R28: 100ohm) is just next to it. The protection diodes (D1..D9) is mounted next to the mA fuse. The voltage input is also a bit uncommon with only a single PTC with series resistor (R25: 470ohm) and a spark gab (Most meters has dual paths with PTC's). This meter do not use protection on the 10Mohm (R1..R4: 4x2.55Mohm) or 1Mohm (R8..R11: 4x250kOhm) paths, but has some fairly large resistors for it.
An interesting detail is all the gold traces, they are guard traces, i.e. placed around sensitive areas and kept at the same voltage usual with an OpAmp, this means very low leakage current from the sensitive area.
Most of the range switching must be electronic, the meter is packed with analog switches: IC1: AD8539, IC3: 4051, IC5: ADG609, IC6: 4053, IC7: ADG409, IC21: AD8539, IC24: ADG711, IC26: 4053 and more. I did also see some OpAmps IC1: AD8539, IC12: AD8539, IC20: AD8539
The big chip (IC31) is probably a UPD78F1518A 16 bit microcontroller and next to it is a 24bit ADC (IC211: ADS1247). The RMS converter is from LT (IC13: LTAFG/LTC1968)
The above list of chips is not complete, it is fairly complicated to build a high-end meter without using a multimeter chipset.

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The above 4 images are for people that want more detailed pictures of the circuit board (Most chip numbers can be seen on them).




Conclusion

This meter is a high-end meter with many functions and very good precision, I also expect the CAT rating is correct. The functions generally works very fine and fast, but I found a few limitations: LPF can only be used on 600V & 1000V range, I am missing duty cycle and average (In some cases the filter function can substitute) and I do not know how useful 400 memory locations are.
The user interface is slightly different to most other multimeters with min/max always active and a CLEAR to reset both min/max and peak without disabling them.

I like the meter, user interface and how fast it is.



Notes

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