Is the Hioki DT4256 Your Next Multimeter?

If there is one measuring instrument that every electronics engineer or electrician must have, it is the multimeter. The available selection of multimeters is enormous and prices range from €10 to thousands of euros. As a serious electronics enthusiast, if you want an accurate, sturdy and reliable meter, you will quickly arrive at an instrument that costs more than a few tenners. In this article, we will look at a robust multimeter, the DT4256, which costs around €200 euros and is made by the Japanese manufacturer Hioki, which is not that well-known here, but nevertheless produces excellent measuring equipment (Figure 1).
  These days, there are not many manufacturers of electronics test equipment who manufacture in their own country, but most of the multimeters from Hioki (including the DT4256 described here) are both designed and manufactured in Japan. That is quite unusual because the majority of multimeters from well-known American manufacturers are manufactured in China nowadays. I was therefore very curious about the DT4256's build quality; for some €200 you would naturally expect an instrument of some class.

The DT4256 complies with the safety classes CAT III 600 V and CAT IV 1000. This makes this meter suitable for taking measurements on the electrical installations of buildings, but also measuring energy meters, primary connections and primary fuses.

Enclosure and Display

The DT4256 is supplied with a set of test leads, 4 AAA batteries and a manual. A storage case, current clamp, USB cable (with galvanic isolation) and a magnetic hanger are available separately. The meter itself has the modest dimensions of 17.5 x 8.5 x 5 cm, so you can therefore easily hold it in one hand. It is provided with a blue holster made from a semi-soft plastic, and the manufacturer even indicates in the specifications that it is drop-proof from a meter onto a concrete floor. I haven't tried this yet, but the meter feels very sturdy, and I suspect that it will indeed survive such a fall without any problems. Another interesting detail from the specifications: the meter is operational over the temperature range from -25 to +65°C. Now, I don't see many other multimeters that can do that!
 
The DT4256 is provided with a display that has a dual readout with 6000 counts (Figure 2). The larger readout shows the measured value, the smaller readout shows, in the AC voltage/current ranges, the frequency of the measured value when the Max/Min function is used. At the bottom of the display is a bar graph that has 32 segments. The measuring functions are: DC voltage and current, true-RMS AC voltage and current (with frequency indication), resistance, capacitance, continuity tester, diode tester and cable finder for live cables. There is a separate setting for the current clamp that is available as an accessory. The voltage and current ranges have (of course) auto-ranging, and there is even a setting where the meter will detect whether there is an AC or DC voltage in the inputs. This is, however, somewhat less accurate than the normal ranges and also has a lower input impedance of 900 kOhm (the other voltage ranges are 10 MΩ).
 

Features and Uses

As I already mentioned, the enclosure seems very sturdy. The rotary switch operates quite smoothly and clicks nicely into the various positions. Below the display there are four pushbuttons, the labelling of which mostly speaks for themselves: Hold/Auto, Max/Min and Range are obvious. A little clarification is required for the Filter/Rel button. This can be used to turn on a low-pass filter with a cut-off frequency of 100 or 500 Hz (Figure 2). This can be useful when making measurements on mains-powered equipment so that higher harmonics will not be included. Present-day mains power supplies are almost always switching power supplies, and these can generate quite dirty pulse-shaped loads. A very useful feature, therefore!
  The power is provided by four AAA batteries. The battery compartment is easily opened with a small screwdriver. Next to the batteries is also the main fuse, rated 11 A/1000 V (Figure 3). This can therefore easily be replaced without having to open the enclosure any further.
 

The update speed of the DT4256 is good; it reacts very quickly to signal changes. According to the manufacturer, the display is refreshed 5× per second and the bar graph even 40×. That makes the bar graph a real convenient aid for adjusting something. Unfortunately, the contrast of the display is a little average, you have to look straight at to be able to read it well. Fortunately, the backlight (using two white LEDs) is very usable. By default, this will turn on for 40 s after pushing the button, but you can also turn it on or off continuously. The meter switches to standby after 15 minutes if no switches have been operated during this time. After 45 minutes, the meter will switch off completely to save power. This function can also be switched off.

The DT4256 is provided with a buzzer that makes a noise under various circumstances. This sound is clear and, in contrast to many other meters, I did not find this buzzer annoying, it beeps only for a short time and only in situations that really require attention. It can also be switched off altogether.

The continuity tester reacts, just like the display, very quickly (within 0.25 s). A value below 25 Ω is considered a connection and is indicated by a combination of the buzzer and a red LED. If you can't hear the buzzer very well because of a noisy environment, then you can always keep an eye on the red LED.

The diode measurement operates at a voltage of about 5 V, but the meter in this range indicates a maximum value of only 1.5 V. With an ordinary diode, it will therefore indicate about 0.6 V, but with a white LED, it remains at 1.5 V. However, the LED does light up faintly, so you can at least check whether the LED actually works.

The Hold function has a special feature where you cannot only freeze the value on the display manually, but with Auto-Hold the meter will freeze a value itself when a varying input signal has stabilized (this function only works with higher input voltages above 120 V).

The cable finder is a useful bonus that I don't find all that necessary for a multimeter, but electricians will certainly find this a welcome addition. On the back of the meter, an (optional) module can be attached that provides an optical connection to a computer. The accompanying PC-software (DMM Communicator) is available from Hioki's website.

DT4256 Accuracy

The specifications of the measurement accuracy of the DT4256 are quite modest. The basic accuracy of V_DC amounts to 0.3%, with V_AC 0.9%. To check this, I carried out different voltage and current measurements and compared the DT4256 with the measurement results from an accurate bench multimeter and a hand-held multimeter with a basic accuracy of 0.02 and 0.03%, respectively. This showed that the DT4256 performed much better than the specs indicate. This shows that during manufacturing and calibration, careful attention has been paid, and precision components have been used. It is, of course, only a single sample of the DT4256 that I compared, but it nevertheless gives me the impression that other examples will perform equally well within the specifications.

The deviation with V_DC amounted to maximum of two counts, i.e. 0.05% (measured up to 50 V). With V_AC I arrived at a deviation of 0.1% max at 100 Hz. At higher frequencies the deviation is a little bigger, but the frequency range for AC measurements only goes up to 1 kHz, according to the manufacturer (it is therefore not a good choice if you intend to use it for audio measurements). At 1.5 kHz, the deviation amounted to 1%, still a very tidy value when we compare it with the specifications from the manufacturer. With DC current measurements, the values were again within 0.05%, excellent once again!

With resistance measurements between 100 Ω and 100 kΩ the deviation was less than 0.1%, also much better than the 0.7% that the manufacturer indicates. With capacitance measurements, I obtained deviations of 1% maximum (manufacturer: 1.9%). I have to mention here that with the capacitance measurement function of multimeters, depending on test voltage and frequency, they can come up with different results, my reference meters couldn't arrive at a unanimous answer either. By the way, the DT4256 is not very suitable for measuring small capacitances, the measurement resolution is 1 nF.
 

 

The Handy DT4256

The Hioki DT4256 is a very handy and robust meter that thanks to its specifications is suitable for both the electrician and the electronics engineer. The number of buttons and functions are kept to a sensible limit, but everything you need for daily use is present. And what is important: the functionality and operation of all the features are well-thought-out. It is the various details that make you notice that Hioki, much better than many other manufacturers, took the user of this instrument into account when designing this meter. And this is what really matters. If you would like a sturdy as well as an accurate multimeter of excellent (Japanese) quality, then I can certainly recommend this DT4256.

Translation: Arthur de Beun