Good Day;
This is the second time I have posted regarding this issue as I didn't get much help on the first posting. To further investigate this behavior I purchased a second unit and evaluated it in hopes that the behavior was due to a faulty device. Unfortunately the second unit exhibited similar behavior showing offset voltages of 100-200 mv. I also have a Hantek 6022BE from a previous course that I taught. This unit exhibits a voltage of less than 10mv, which I can live with. So HANTEK clearly knows how to design a scope front end with a reasonable offset. Unfortunately the voltage offset behavior of the Hantek 2D42 is unacceptable for educational purposes (Honestly I can't think of an application where it would be acceptable). For this reason I AM NOT going to recommend going forward with the purchase of these units for our courses. Should Hantek be willing to contact me and resolve this issue, I am willing to listen as the rest of the functionality, form factor, and price are nearly perfect for introductory engineering courses.
What follows is my first post which contains more technical information. This description is accurate for both units. Yes, I did multiple self calibrations after warming up, but they seemed to have little affect.
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
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Post time 2023-1-26 06:20:21
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