Motor test bench using Hantek-1008 oscilloscope ODD READINGS

[crossbreak]

Hi,

i'd like to build a Motor test stand for both friction drive and hub motors. Two motor work agains each other, one as motor, one as generator. As a load I want to use cheap $0.30 12V Halogen Lamps and some FETs that do PWM between the 3 phase leads.

Primary setup: MagicPie2 against N6354 friction drive.

Measurement:

-Speed or rpm (both motors) using a PAS-Sensor as a Probe
-Torque (MagicPie2 only) using a strain gauge from a digital scale
-Battery Current via a 10mOhm shunt
-Battery Voltage
-Phase current of both motors

Arduino will be connected to both the throttle and do the PWM for the Load Fets. This way I can simulate certain drive circumstances (bike weight, speed, elevation etc.) and repeat it over and over again.

The Probes get connected to a cheap 12-bit Hantek 1008 8-channel USB oscilloscope.

My Problem: The Hantek gives odd reading above 5Volts. If I switch to 50V (for the battery voltage), it ouputs 171V or 166V. I tried all 8 channels, it's all the same. The last chance I see is to use a via a 10:1 voltage divider to get my battery voltage into the 5V range. Any ideas what could be wrong?

 

[bearing]

What are you measuring, and where do you connect the probe ground and signal clips?

Edit: Are you using a 1:10 probe?

 

[dnmun]

sounds like the USB scope is not calibrated for the laptop. did they send you a calibration procedure with the device?

 

[bearing]

That's new to me. Why do you need to calibrate it after switching computer?

 

[heathyoung]

Yep - the joys of USB scopes... They use the port voltage as a reference for some reason.

Me - I stick to glass, phospor and electron beams

 

[crossbreak]

I use a software 1:10 probe. Maybe I should power it with a better power supply, like a an 7805 voltage regulator bihind a 2s lipo battery ? Can only do zero calibration.
I'll use it with a 1:10 hardware probe, but i still want this problem to be solved :x Maybe the preamps are some how working wrong? STM32 can only measure up to 5V, doesnt it?

I've got another issue, I can only read exactly 2000 samples. I should write the hantek support :?

 

[bearing]

What is a "software 10:1 probe"?

My guess is that when you set it to 10:1 in software, you are telling it that you have a hardware 10:1 probe connected, so that it will multiply it's ADC readings by 10.

But since you are using the standard 1:1 probe, it will show 10 times more than what it's actually reading. And when you connect the 1:1 probe to the battery, it will clamp the input at 16V, which will show up as 160V on the screen.

 

[crossbreak]

I thought the osci has built in voltage dividers. If I chose 1:10 probe, it sets the right voltage divider, for example 900kOhm/100kOhm. just like any ,multimeter does.

Thanks a lot for you help, i'll try that!

 

[heathyoung]

NO - if you select 1:10 in software, that is the probe setting you need to use!

 

[crossbreak]

yeah, thx for the help, I've got a 1MOhm poti as a probe now, works fine and I can fine tune or colibrate my probe using with a more expensive Multimeter.

The 2000 samples problem: I now use the hantek 1008 with Labview, much better for me than the software that it comes with Thx for your help, I'll report more on my test bench and the readings.

 

[ef.avelar]

Hi crossbreak,

I know that is a little bit late since the post was created, but I would like to know where did you get the .vi (LabView) to work with you Hantek 1008 PC scope nicely?


Thanks!