Timeline for When measuring AC via an ADC, is it bad to have common ground?
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
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| Nov 27, 2011 at 18:30 | answer | added | The Photon | timeline score: 1 | |
| Nov 27, 2011 at 17:22 | history | tweeted | twitter.com/#!/StackElectronix/status/140843050288164864 | ||
| Nov 27, 2011 at 7:39 | answer | added | Oli Glaser | timeline score: 3 | |
| Nov 27, 2011 at 6:27 | history | edited | Dustin | CC BY-SA 3.0 |
added some data and updated the schematic
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| Nov 27, 2011 at 2:29 | comment | added | The Photon | let us continue this discussion in chat | |
| Nov 27, 2011 at 2:27 | comment | added | The Photon | It looks like the guy with the website has a meter that produces 100 uA dc current when clamped around an wire carrying 30 A AC. His circuit will give 5 V output when the measured current is 30 A. It's not obvious that the SCT device you're using is producing an AC or a DC output signal. Since it's called a "transformer", I'd guess an AC output signal. This probably means the circuit you're using is not the complete solution for you. You might need to add a rectifier circuit to convert to DC, and adjust the gain of the LM358 circuit depending on the scaling you want in your measurement. | |
| Nov 27, 2011 at 2:17 | comment | added | Dustin | I measure a pretty good 60Hz off the input when the capacitor isn't there. | |
| Nov 27, 2011 at 2:12 | comment | added | Dustin | To be honest, I don't know how to measure the current. The specs on the device are pretty poor and I don't have a current meter. I can tell you the highest voltage I've measured off of it was around -48mV - 160mV (possibly lower, I got cut off). | |
| Nov 27, 2011 at 2:09 | comment | added | The Photon | Another possible issue is that you've got a low-pass filter with a cut-off frequency of 0.03 Hz. If your "AC" signal is actually slower than that, most of us wouldn't call it "AC" at all -- we'd just call it a varying DC value. So what is the frequency of your AC signal? | |
| Nov 27, 2011 at 2:08 | comment | added | Dustin | I'm getting meaningful looking measurements with it (voltage goes up proportional to input). I got the circuit from this site. I don't fully understand it, so I just apply things I find and measure. I'm getting payback for all the programmers I've shaken my head at over the years. | |
| Nov 27, 2011 at 2:05 | comment | added | The Photon | Another possible issue is that the gain seems fairly high. If the source produces 1 mA when shorted, your circuit will try to produce a 50 V signal at the "signal" node. It would help to know more about the source --- what do you mean by "low voltage" and "low current"? Are we talking milliamps or nanoamps here? | |
| Nov 27, 2011 at 2:03 | comment | added | The Photon | The first issue I see is that your input (pin 2 of the connector) is effectively shorted to ground. Will the source be happy if its output is shorted? | |
| Nov 27, 2011 at 1:53 | history | asked | Dustin | CC BY-SA 3.0 |