A look at the waveforms from a CNC EDM

I decided to try out my new Hantek DS1060 and get some waveforms from the head of the EDM (Electrical Discharge Machine). The probe was hooked to the head of the machine and the ground was connected to the frame. I only took a few measurements but it may be interesting to some to see what the pulses look like when it’s cutting. This cut was burning at 75us on and 37us off.

This is the waveform while cutting at 75us on and 37us off. 8A current
This is the waveform while cutting at 75us on and 37us off. 8A current

You can see that the voltage doesn’t drop to zero, and there seems to be a dropoff after the ionization path has started to cut the material. These dropoffs after the spike seems to indicate that the path is ionized and current control has kicked in, providing 8 amps. Once the time is up, the current shuts off and then there is a ringing spike, perhaps due to inductance. From there the voltage doesn’t reach zero but probably sits at a continuity testing voltage for a little under the 37us. From what I can tell, 75us is started from when the ionization path is established, and 37us is the time it cuts off the current, event though there is still voltage (and maybe a bit of capacitiance).

A view of the measurements taken from the oscilloscope
A view of the measurements taken from the oscilloscope

The measurements seem to correlate to the settings a bit. The EDM itself is set for a 240V cutting voltage so the VMax of 181V is pretty close. I think those values are a quite flexible, I know that before it cuts at all, the voltage is at approximately 240VDC.

Anyways, I thought this would be interesting to post since some people are into EDM machines. I may take some waveforms from the wire EDM and two more different EDM’s. Here’s a final image of a zoomed in view of the peak.

A wider view of the burning process, the short ringing spike must be a check for proximity
A wider view of the burning process, the short ringing spike must be a check for proximity or from inductance

A quick review of the HPS10se portable Oscilloscope from Velleman

I ordered this device about a year and a half ago for about $130USD. When I got it, I wasn’t terribly impressed but overall, for the price it’s not a bad unit. I figured it’s be nice to provide a short review of the device since there aren’t very many useful reviews out there. I have also done a video review which is posted on this page and on my Youtube channel at http://www.youtube.com/user/ElectroTark.


HPS10se Velleman Oscilloscope on the bench
HPS10se Velleman Oscilloscope on the bench

The HPS10se is a low cost oscilloscope with a backlit 128×64 screen. The video performance is actually OK and the waveform is reasonably easy to make out in most instances. This device boasts a 2MHZ bandwidth for analog signals and a 10MS/s sampling rate. While I have no doubt that these figures are true, my own tests show that any waveform shows severe degradation above about 1MHz, this is to be expected though.

HPS10se oscilloscope in the box

The unit comes with a single probe, no need for more since it only has one channel input. 🙂
There is an option on the probe for x10 measurement which can be handy for high voltage measurement up to 600V. I’ve never used that feature on this but it’s easy to access with only a single button press. The device takes 5 AA batteries and can be run with an external wall wart, though it isn’t included. I use an old 9V converter with a 2.1mm by 5.5mm barrel connector, seems to work OK. It is rated at 9V and you might be able to use a 12V pack, though it may generate extra heat on the DC converter on-board.
One problem I have with this device is the way it eats batteries, even when it’s off. Remember to remove the batteries when you’re not using it. As an extra note, it can charge NIMH batteries if they’re in there.

Oscilloscope with a square wave

The device has some standard measurement options such as V-Peak+, V-Peak-, V-Range and Watts and dB. Since this is a low cost unit, it does not have a direct measurement for frequency and you cannot set the trigger level, you can however set its slope (Fall and Rise). You have to measure the frequency indirectly either by looking at the ticks and counting or by using the markers that you set, moving the markers to the start and end of one waveform gives you a frequency measurement in Hz.
Here’s a quick video I made, watch it if you like…


Anyways, here are some pros and cons.
PROS:

  • Low cost, about $130 to $160
  • Reasonable feature set for the price
  • Screen is easy to read despite its low resolution
  • Good for general use, low frequency stuff in a pinch

CONS:

  • Eats batteries like candy, also an odd number to use, 5, which most batteries come in multiples of 2
  • Waveform display is kind of inaccurate
  • Stand flap on back is too short, tough to stand vertically
  • No trigger level function
  • No direct frequency measurement

In closing, I would recommend this for people getting into electronics but for doing anything else, spend the extra money for a good/decent oscilloscope. The price, again, is pretty good.