AlienTek DM40C New Multimeter with some benefits [DM40A - DM40B - DM40C]

[jebem]

Got my DM40C today. What a nice piece of equipment. Very good indeed.

First impressions:

1. Very good multimeter on resistance, current and voltage. The supplied test leads are excellent with just 0.05R total resistance, common probes will measure 0.1R.

2. The capacitance meter is good but it's internal capacitance is around 32pF, with leads 65pF, so can't measure capacitance below 300pF accurately.

3. The frequency meter on the DM40C is specified to be from 10Hz to 60MHz. Furthermore, in the user manual ( page 8 ) they say that the signal amplitude should be within a minimum of 20Vrms and maximum of 250Vrms !!!
So it only works under large signal amplitudes.
I wonder what was their design choice here. It was much more useful if it could read low level signals, or at least in the common 1 to 3V region.

I do not have access to my signal generator where I am, so used a small oscilloscope with signal generator that can only supply signals around 1Vrms.
Under these conditions, and using sinusoidal waveform, the DM40C worked fine in the MHz region up to 4MHz where my poor signal generator dropped the signal below 1Vrms.

4. The signal generator is ok to calibrate the oscilloscope probes.
The sinusoidal and square waveforms are good up to the frequency limit but the triangular and sawtooth are deformed at the higher side of the frequency spectrum.
Additionally, the signal generator stops working when selectin the DMM function, although it keeps working when selecting the Oscilloscope function.
 

5. The 10MHz single channel oscilloscope is good. It acquires and trigger signals well above the specified bandwidth and handle low level signals well.
It is a nice addition, despite the poor bandwidth and single channel.

[Awp]

As for the accuracy of this multimeter, it was tested in this review:
https://s-audio.systems/blog/alientek-dm40c

[Taimer81]

There are differences between the models.

[Aldo22]

As for the accuracy of this multimeter, it was tested in this review:
https://s-audio.systems/blog/alientek-dm40c

That looks very good in part, but does it not show the μV digit?
ZT-225 has three decimal places in the mV range.

[danno_cj]

TC1746B6 precision resistor network divider which has 0.1% precision and 10ppm thermal stability was change with regular resistors. DM40A would have a lower precision and bigger thermal drift compared with DM40C.

ZT-225 has three decimal places in the mV range because has 25mV scale. The lowest voltage range for DM40C is 600 mV. In order to have microvolts resolution the DM40C should have 60mV range, which is missing.

[Aldo22]

3. The frequency meter on the DM40C is specified to be from 10Hz to 60MHz. Furthermore, in the user manual ( page 8 ) they say that the signal amplitude should be within a minimum of 20Vrms and maximum of 250Vrms !!!
So it only works under large signal amplitudes.

Have you checked that?
That can't be right.
The manual says: “For frequency measurement, the recommended input signal amplitude is within 20Vrms, with a limit of 250Vrms.”

[jebem]

I guess that something was lost in translation from Chinese to English.

Taking the literal "recommended" expression, the signal source should be within the recommended 20Vrms to a maximum of 250Vrms.
For me it is clear that the meter requires several Volts to be able to read frequencies from 10Hz to 60MHz.

I wonder why... The simpler explanation is that the frequency bandwidth is narrower than 10Hz to 60MHz, therefore an higher signal amplitude is required to compensate for the attenuation on extremes.
 
Anyhow, I tested successfully from a few kHz to 4 MHz with a basic 1Vrms signal generator.
My guess is that these frequencies are well inside the frequency bandwidth of the DM40C and 1Vrms is sufficient to be registered succefully.

Realistically, the practical application of such low sensitivity frequency meter is very small.

Maybe one of our members have a proper signal generator able to supply above 1Vrms and check the sensitivity and frequency response of our DM40x meter?

 

[Aldo22]

I guess that something was lost in translation from Chinese to English.

I also believe that this is a translation problem.
I mean 20Vrms sine is almost 57Vpp.
Normal signal generators can generate around 20Vpp. Less at higher frequencies.
That just doesn't make sense.

[jebem]

I guess that something was lost in translation from Chinese to English.

I also believe that this is a translation problem.
I mean 20Vrms sine is almost 57Vpp.
Normal signal generators can generate around 20Vpp. Less at higher frequencies.
That just doesn't make sense.

Yap, 20Vrms is way to low sensitivity.
The test I did prove that it can read up to 4MHz with just 1Vrms, the limit of my poor signal generator.

A better DSO would be needed to find out what is the minimum trigger level along all the frequency band.

I have been reading on AliExpress buyers comments.
One in particular was unhappy with the DM40C because he was expecting to be able to read the 32.768kHz clock oscillator signal in his workplace and it failed to trigger the signal.
As he said, while we can switch from DMM to Oscilloscope to take the clock reading, it is not as convenient as being able to take all readings in DMM mode.
He also mentioned a Fluke they have at work that can read it without issues (this one remark goes against the Alientek Marketing team that tries to associate the DM40 to the Fluke top series).

Despite this minor Frequency low sensitivity issue, I like the DM40C for what it does well.
The last digit will take time to stabilize and may not fix the value, but I see this as normal on these low cost devices.

Pictures taken using the included stock probes:

1: Device information
2: Reading mains AC interference from my body (240VAC @ 50Hz in my location)
3. Probes loosely shorted, last digit slowly change between 0 and 1
4. Probes shorted with alligators
5. Mains reading (240VAC nominal at 50Hz in my location)
6. 0.01R 0.1% resistor, last digit slowly bounces between 1 and 2
7. 50MR 5% High Voltage resistor
8. 1R 0.1% resistor
9. 10MR 0.1% resistor
10. 0.1R 0.1% resistor

[jebem]

Some random, non controlled, frequency tests.

Pictures:

01. 1.00 kHz sinus signal from the device at right, as seen by the DM40C DMM ACV scale
02. Same signal as seen by the DM40C DMM Hz scale

03. 1.00 MHz sinus signal from the device at right, as seen by the DM40C Oscilloscope (reading 1.52 Vrms)
04. Same signal as seen by the DM40C DMM Hz scale

05. 4.00 MHz sinus signal from the device at right, as seen by the DM40C Oscilloscope (reading 1.42 Vrms)
06. Same signal as seen by the DM40C DMM Hz scale
(The DM40C could not read above 4 MHz because the SG amplitude at 5 MHz and up is insufficient)

07. 1 kHz sinus signal from the DM40C SG at left, seen on both oscilloscope devices (1.81 Vrms vs 1.74 Vrms)
08. 50 kHz sinus signal from the DM40C SG at left, seen on both oscilloscope devices (1.66 Vrms vs 1.63 Vrms)

[jebem]

Some random testing on capacitance measurements.


Pictures:
C01. DM40C without test leads inserted: 32 pF stable reading after a few seconds. Will not give a lower reading.
C02. With test leads inserted: 63 pF stable reading, as long as cables are not touched.

C03. Reading a 221 (220 pF) capacitor: 284 pF - A very good reading if we subtract 63 pF parasitic from it to get 221 pF. Close to the ZT-DQ02 LCR is reading.
(these are common non branded caps with no declared tolerance)

C04. Reading a 470 uF electrolytic capacitor: 445.0 uF - A good reading, close to what a ZT-DQ02 LCR set to 0.6V / 100 Hz is reading.

[jebem]

For some strange reason, I thought that Alientek forgot to include a REL key.
After all it was my fault. I totally forgot to properly read the damn manual.

Concerning the low capacitance measurement, enabling the RLE feature (via touch screen soft key) will properly read my 10pF capacitors without issues.
The only procedure to follow is to give a few seconds to let the DMM stabilize itself for each input condition.

Pictures:
RLE_disabled - Shows the parasitic capacitance seen by the DMM using the stock leads, plus a pair of alligators from another equipment.
RLE_enabled - Enabling the Relative measurement will null the reading.
RLE_10pF - The smallest cap (10pF) I have access at the moment, successfully registered.
RLE_220pF - The 220pF is measured perfectly as well.

Did I mention the almost luxurious box the DM40 came packaged in?
Inside, a cut-out foam bed cradles the equipment.
Although I would trade the box for a pouch to hold all the test leads and probes. Unfortunately the store did not offer that option.

[jebem]

I like to do some reverse engineering of my equipment internals. At least have a part listing with parts datasheets.

After some Internet searching I have a partial hardware parts listing. Thanks for this forum, some Russian and Chinese sites for internal pictures and discussion.

PARTS for DM40C version

Motherboard PCB reference: DM40 V1.1

BATT   LN425272           Battery LiPo 3.7V 2000mAh 7.4Wh with protection circuit
IC   HY3131       DMM front end, one High-precision 24-bit ADC, two high-speed 19-bit ADCs,
XTAL   4.9152 MHz   Crystal oscillator for HY3131
IC   MAX6190            High-precision voltage reference chip 5PPM/C
UN   metallic box   Shielded case - Oscilloscope analog vertical amplifier??
IC   GD32F427VGT6   MCU 32-bit Cortex M4 core, 200 MHz, 1 MB ROM, 256 KB RAM
XTAL   26.000 MHz   Crystal oscillator for MCU
IC   W25Q128JV   128Mb memory
IC   BP2A838-20A2   8-pin by JL (Zhuhai Jieli Technology Co., LTD), BT Bluetooth chip
XTAL   24.000 MHz   Crystal oscillator for BT IC
IC   EL3H7       Optocoupler
IC   EL3H7       Optocoupler
IC   CA-IS3741HW    By ChipAnalog, High-Speed Four-Channel Digital Isolators
IC   LT61-117           6-pin VPS8505  transformer
IC   LT61-113           6-pin VPS8505  transformer
IC   VPS8504B    Micropower Isolation Power Supply
IC   VPS8504B    Micropower Isolation Power Supply
IC   TP4056       Battery charging management
IC   HC4051       Single-channel analog multiplexer/multiplexer,
IC   3PA1030            By 3peak, 10-Bit, 50-MSPS, CMOS Analog-to-Digital Converter
IC   TC1746B6    High-precision voltage divider resistor network divider (DM40A does not use it - Just a few resistors in its place)
IC   RUH30J51M    By Ruijun Semiconductor (Ruichips), dual-channel symmetrical N-channel MOSFET field effect tube, current 50A, withstand voltage 30V
K   HFD4/3-LS   By Hongfa, Subminiature signal relay of 4th generation, DPDT, 100MHz contacts,  3V / 90R coil
IC   174 F163H   4-pin smd  (DM40A uses 174 F215H) - Optocoupler
IC   174 F163H   4-pin smd  (DM40A uses 174 F215H) - Optocoupler
D's   SD              B0520LW   Schottky Barrir Diode 20V 500mA


Concerning the unidentified chips, I put a question on the another thread at:
https://www.eevblog.com/forum/chat/what_s-this-please-(component-advice)/msg5964329/#msg5964329

Hopefully someone will know what these chips are. datasheets would be nice too.

EDIT: Many Thanks to Gamalot member who was able to identify the unknown components above.
https://www.eevblog.com/forum/profile/?u=112468

[jebem]

Revisiting the less than optimal Frequency readings of the DM40C.

I got a better low cost signal generator - the Juntek JDS-2900-60M, able to deliver a minimum of 5Vpp at 60MHz on sinusoidal waveform.
I checked the output signal with a 120MHz oscilloscope, so even assuming an error of 10% of the oscilloscope readings, the signal generator sustains the claimed specifications
 
Took a few random tests on the DM40C.

What I see is a severe decreasing in sensitivity with increasing frequency. So the bandwidth seems to be very poor.

It requires a minimum of:
-> 50 mVpp to register low frequencies up to a few kilo-hundred Hertz;
-> 1.7 Vpp at 10MHz;
-> 6 Vpp at 20MHz;
-> More than 10 Vpp at 30MHz and above. How much more I can't tell, as the SG is limited to 20Vpp up to 10MHz, 10Vpp between 10MHz and 30MHz, and 5Vpp above 30MHz.

In the end I tend to believe that the Alientek statements found in the User Manual are actually credible to some extent.

Pictures:
1. 50mVpp at 60kHz - Ok
2. 40mVpp at 60kHz - Fail
3. 50mVpp at 10kHz - OK
4. 1.7Vpp at 10MHz - OK
5. 1.6Vpp at 10MHz - Fail
6. 6Vpp at 20MHz - OK
7. 5Vpp at 20MHz - Fail
8. 10Vpp at 30MHz - Fail

[Aldo22]

Revisiting the less than optimal Frequency readings of the DM40C.

I think this is pretty normal for a frequency counter in a DMM.
To be honest, at > 1kHz I use the oscilloscope anyway, so I'm generally not that interested in this feature.

[jebem]

Revisiting the less than optimal Frequency readings of the DM40C.

I think this is pretty normal for a frequency counter in a DMM.
To be honest, at > 1kHz I use the oscilloscope anyway, so I'm generally not that interested in this feature.

Absolutely, I didn't bought this one thinking it could be a useful frequency counter. A digital oscilloscope is good enough for most applications.  For precise measurements I use my vintage professional Fluke 1920A.
(I used these Flukes on my job as a RF telecom engineer back in the late 70's. I bought one of them at the time and later converted it from batteries to AC outlet only, by adding a power supply regulator to get rid of those pesky NiCd cells)

[Aldo22]

Absolutely, I didn't bought this one thinking it could be a useful frequency counter. A digital oscilloscope is good enough for most applications.

A more interesting test would be to check if the AC accuracy is really ±(0.3%+15d) up to 10kHz. According to the specifications it should be able to do that, afaics.
That would be a small advantage over other inexpensive DMMs.

[easa]

For some reason, no one noticed that such an advanced device does not show an incorrect connection of measuring probes in terminals. When trying to measure the voltage when the probes are in terminals for measuring the current.

[S2084]

New firmware version and android application
https://t.me/S2084K/15773/26022

[BH3XON]

I understand that the voltage divider resistors for A and B/C differ in both accuracy and package,

so I’m considering getting the DM40B as the most cost-effective option.

By the way, do you know if the DM40 can display both current and voltage at the same time?

Something like the FLUKE 8808A, where you can press Shift + C/V to show both simultaneously.

That would be really handy when testing power supply input and output, even if there’s some error introduced by wire losses.

Revisiting the less than optimal Frequency readings of the DM40C.

I think this is pretty normal for a frequency counter in a DMM.
To be honest, at > 1kHz I use the oscilloscope anyway, so I'm generally not that interested in this feature.

[jebem]

For some reason, no one noticed that such an advanced device does not show an incorrect connection of measuring probes in terminals. When trying to measure the voltage when the probes are in terminals for measuring the current.

As far as I know, in this model there are no warnings of any form if the user makes such a mistake - I expect to see the built-in 10A  ceramic fuse to blow off.
But that is the normal way multimeters work, even top brands.
Yes, some models will warn about mistakes, and just a very few will block you from making mistakes, the rest of it will allow you to go ahead and blow the current fuse as well.

[jebem]

By the way, do you know if the DM40 can display both current and voltage at the same time?

That is not possible as far as I know.
You select only one single option at a time from the offered six function buttons seen in the touch screen: V, A, R, C, D, Hz.
Also, I wouldn't connect this DMM test leads to measure Voltage and Current at the same time. You either insert the red test lead into the panel V/R/C/D/Hz upper socket, or to the A/mA/uA lower socket.

[BH3XON]

By the way, do you know if the DM40 can display both current and voltage at the same time?

That is not possible as far as I know.
You select only one single option at a time from the offered six function buttons seen in the touch screen: V, A, R, C, D, Hz.
Also, I wouldn't connect this DMM test leads to measure Voltage and Current at the same time. You either insert the red test lead into the panel V/R/C/D/Hz upper socket, or to the A/mA/uA lower socket.

It would be great if it had that feature — even better if it could calculate and display power as well.
The FLUKE 8808A can show both voltage and current simultaneously, and while there’s some inaccuracy due to voltage drop across the wires, it's still very convenient for quick, rough measurements.

[VASILISK]

I have made a new video you can watch it about the model c .

✨Alientek DM40C 3 in1 Multimeter Oscilloscope & Signal Generator - full Review & Tear Down✨

https://youtu.be/-CCQZ08o6qM?si=iZgEcIpw3J2QdWVF

[nukie]

My eyes are too old for my HP mono LCD benchtop boat anchor DMMs. So, I am looking for a unit with bigger display. I don't care for the oscilloscope function, I already have one. I am planning to mount this on a DIY arm to free up my deskspace, plus I hate DMM leads all over my desk. So I am thinking I can swing this away from the desk when I don't need it.

I don't have time to shift through YouTube vids but I have a few questions. How long does this unit take to boot up? Is there a setting where you can have DMM on default or do you have to select the DMM function every time it's booted up?

I've looked at many DMM with colour LCD screen so far this is the most interesting unit, I really like the portrait form factor and it's not heavy n bulky.