HANTEK 2D42 Offset Voltage

erissberger

Good Day;

I am a instructor at Oregon State University, and I purchased a Hantek 2D42 Handheld Oscilloscope for evaluation to include in a college level introductory Electronics Class.     If approved it would be about 300 units per year.   We are attracted to this unit due to the integration of Oscope, DMM (with Capacitance), and AWG in one package.      The students will usually be utilizing the device when connected to a computer via USB, and our overall measurement and functional requirements are very, very, easy.

In executing one of the labs, I discovered that my unit has a DC bias/offset on the O-scope reading of between 100 and 300 mv depending on the configuration.     While we have easy measurement requirements, this is too large of an offset to accomidate.     I am wondering if I have a defective unit or if this is common to the device?      If this is a common behavior we will not be able to use this device.    If my unit is defective I will want to acquire another unit to verify it was a single unit problem.

More technical data:
Setup a simple cirucit consisting of the inegrated AWG as a 1Khz +/- 1V sine wave generator.     The signal runs through a 1K resistor and a 0.1 microfarad capacitor.  The O-scope channel #2 is connector to the input side of the 1K resistor (e.g. the output of the AWG), and channel #1 is connected to the output of the resistor (e.g. includes the phase shift and amplitude of the RC combination).      


A O-Scope Plot is shown below.



It can be seen that the offset is around 100mv, which is too much.     This can be visually verified by examining the waveforms relative to the grid and zero point, as well as the mean measurement.     The peak to peak measurement is correct, indicating it is a pure offset.     


Additional behavior I observed investigating this problem.

1) The offset is affected by the veritical scale.    Reducing the vertical to 1V/div  or 2V/div will increase it upto about 300 mv.

2) The offset doesn't appear to be affected by thehorizontal scale.

3) I believe it is the O-scope and not the AWG as I utilizedan external signal generator and got pretty much the same O-scope behavior.

4) Turning off Channel #1 display affects the behavior.     Depending on circumstances which I don'tfully understand it can drop as low as less than 10 microvolts to 50milivolts.   This behavior is notconsistent.

5)  Having the unitplugged into the USB port also can affect the behavior.    In one case I operated totally as a handheld device and had a ~100 mv offset, but when I plugged it into my laptop USBit grew to ~200 mv (Operating the unit purely as a hand held is not a goodsolution for our use case).

6) I did the basic debuging steps;    Performed calibration after 20 minutewarmup, verified AC coupling, etc......

Thanks Ed Rissberger

Jing

Dear Sir，
May I ask whether you have carried out self-calibration of the machine? It is in the Menu menu. The machine is self-calibrated after at least 30 minutes of heat and without any wires connected. After the machine has been self-calibrated, does the offset problem still exist?

erissberger

Yes, I performed a self calibration.    Actually I did it multiple times hoping it would be a magic fix for the issue.

Thanks Ed

erissberger

Jing replied at 2023-1-14 16:04
Dear Sir，
May I ask whether you have carried out self-calibration of the machine? It is in the M ...

Yes, I performed a self calibration.    Actually I did it multiple times hoping it would be a magic fix for the issue.   I still see the voltage offset

Thanks Ed

any1ne

That's all
Lol.
Great help..

richard.lounsbury@snet.net

Was the cap completely discharged from the start?