PicoScope 7 Automotive
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need help understanding this 220 volt AC waveform
need help understanding this 220 volt AC waveform
I have been unable to find anything online to help me understand what is going on in this waveform. I am hoping somebody on this site should be able to figure it out.
This is a 220 volt AC, capacitor start ,single phase deep well pump. It has 2 line voltage wires and one ground wire. I am using pico TA018 amp clamps set on 100mv / amp scale clamped on the 2 line voltage leads and a 3423 scope. This pump has an electronic pump protection module that monitors the amperage the pump is pulling. If the amperage drops 20% it thinks the well is running out of water and turns the pump off. It will also turn the pump off if the current increases by 20%. The system has an iron filter that requires a 30-minute regeneration cycle every 48 hours. At approximately 29 minutes the pump starts pulling too much amperage and the protection module turn it off. The attached waveform shows a complete regen cycle with the pump turned off by the module. The amp clamps are before the protection module.
First thing I don't understand is, the amperage shown on the scope doesn't agree with 3 true RMS clamp meters. The meters all show 10.6 amps when the pump is running, but the scope shows 1.7 volt from zero to voltage peaks. This would be 17 amps, multiplied by .707 = 12 amps. Why the 1.4 amp difference? Even if I average the peaks it comes to 11.5 amps.
Secondly, when the pump first turns on, and when it pulls to much current before being turned off, the wave form goes 1.8 v above zero but 3.4 v below zero. I don't understand how an AC circuit could have more amperage below zero than above.
Lastly, when the pump begins running the peaks in the waveform are fairly even, but when it starts pulling excess current before turning off, the upper part of the wave is fairly even but the lower part of the wave is varying about 850mv in a repeatable pattern. If this was DC fuel pump I would think it had 16 commutator segments and my amp clamp needed to be inverted. The pump mfg was unable to provide any information about the pump construction. I don't think it's heating up because the rpm doesn't change, but I have no idea what's happening to cause the current increase. I would be very appreciated if someone could help me with this.
This is a 220 volt AC, capacitor start ,single phase deep well pump. It has 2 line voltage wires and one ground wire. I am using pico TA018 amp clamps set on 100mv / amp scale clamped on the 2 line voltage leads and a 3423 scope. This pump has an electronic pump protection module that monitors the amperage the pump is pulling. If the amperage drops 20% it thinks the well is running out of water and turns the pump off. It will also turn the pump off if the current increases by 20%. The system has an iron filter that requires a 30-minute regeneration cycle every 48 hours. At approximately 29 minutes the pump starts pulling too much amperage and the protection module turn it off. The attached waveform shows a complete regen cycle with the pump turned off by the module. The amp clamps are before the protection module.
First thing I don't understand is, the amperage shown on the scope doesn't agree with 3 true RMS clamp meters. The meters all show 10.6 amps when the pump is running, but the scope shows 1.7 volt from zero to voltage peaks. This would be 17 amps, multiplied by .707 = 12 amps. Why the 1.4 amp difference? Even if I average the peaks it comes to 11.5 amps.
Secondly, when the pump first turns on, and when it pulls to much current before being turned off, the wave form goes 1.8 v above zero but 3.4 v below zero. I don't understand how an AC circuit could have more amperage below zero than above.
Lastly, when the pump begins running the peaks in the waveform are fairly even, but when it starts pulling excess current before turning off, the upper part of the wave is fairly even but the lower part of the wave is varying about 850mv in a repeatable pattern. If this was DC fuel pump I would think it had 16 commutator segments and my amp clamp needed to be inverted. The pump mfg was unable to provide any information about the pump construction. I don't think it's heating up because the rpm doesn't change, but I have no idea what's happening to cause the current increase. I would be very appreciated if someone could help me with this.
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- tripped protection module 2.psdata
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Re: need help understanding this 220 volt AC waveform
You post this under automotive side of the forum, using non-automotive scope and in the electrical vehicle section.
Not sure I would use your services though
Not sure I would use your services though
Re: need help understanding this 220 volt AC waveform
I couldn't think of where else to post it. I was hoping someone that understood 3 phase electric vehicles motors would be able to explain this. Do you know of another forum that might help?
Re: need help understanding this 220 volt AC waveform
I am using a 3423 automotive scope and pico 6 automotive
Re: need help understanding this 220 volt AC waveform
I was unaware this was automotive scope. I’ll have a look in your capture later in the day. There is also a test and measurement forum:
https://www.picotech.com/support/index. ... bfe415a744
How many here have the qualification to even touch a orange cable in a EV? Very little. Your audience is maybe 10. On T&M maybe 450 know 3 phase and winding assisted single phase motor starters.
https://www.picotech.com/support/index. ... bfe415a744
How many here have the qualification to even touch a orange cable in a EV? Very little. Your audience is maybe 10. On T&M maybe 450 know 3 phase and winding assisted single phase motor starters.
Re: need help understanding this 220 volt AC waveform
When you say clamps set on 100mv / amp scale clamped on the 2 line voltage leads, can you please clarify?
This ?
What are other system components and can you provide an P&ID for our understanding?
For the current measurement problem, did you forgot a multiplier maybe?
Vpp = 2 x Vp = 2 √ 2 x Vrms
Are you aware that pico software under Measurements, can do RMS?
Hope this helps to give some directions.
An AC system will balance around 0 if in symmetry so to speak. You might have a ground fault disturbing this balance but without an P&ID and electrical diagram, it is hard to say.
This ?
What are other system components and can you provide an P&ID for our understanding?
For the current measurement problem, did you forgot a multiplier maybe?
Vpp = 2 x Vp = 2 √ 2 x Vrms
Are you aware that pico software under Measurements, can do RMS?
Hope this helps to give some directions.
An AC system will balance around 0 if in symmetry so to speak. You might have a ground fault disturbing this balance but without an P&ID and electrical diagram, it is hard to say.
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Re: need help understanding this 220 volt AC waveform
Thanks. I never thought about using RMS setting in pico. I have attached a circuit diagram and photos of the mfg diagrams for the pump protection module and capacitor / starter boxes. I think I will replace the run capacitor and see if helps. I will also post it in the T&M forum. I'm really curious about the amperage being unequal above and below zero only when the current increases above normal. I have always had trouble completely understanding AC voltage.
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