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Misc Electronic Questions

Discussion in 'General Electronics Chat' started by Billy Mayo, Apr 4, 2013.

  1. Billy Mayo

    Billy Mayo Member

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    What is circulating current? and Reactive loads?

    With a current meter it measure amps , but since it's circulating current it's different why?

    When it's circulation current it's a reactive load?

    "A non linear load means the current and voltage are not in phase"
    "A linear load means the current and voltage are in phase"
    " Reactive Load means? circulating current

    A light Bulb is a linear load

    Using a Transformer and a light bulb will be a Non-Linear load because of the transformer? the transformer puts the current and voltage not in phase? because its a inductor + resistor , phases are not in phase ?

    What power supplies are High Impedance? is it tube, solid state, switching power supplies, Linear power supplies, how do you know or tell?

    What power supplies are Low Impedance? is it tube, solid state, switching power supplies, Linear power supplies, how do you know or tell?

    A High Impedance power supply creates a voltage drop, but what makes a power supply high impedance? or low impedance?

    What is DC component?

    At my work , they say DC component is the "TIME GAP" or " Cross over" section between the positive and negative cycles at the zero crossing point when you have a push pull network

    Is this Time gap or Cross over called DC component?

    When You have a PWM push pull output stage , the DC component is an adjustment to center the Positive and Negative cycles AC waveform to zero volts. If you don't then there will be a time gap which is called DC component

    I'm not sure the difference between DC component VS DC offset
     
  2. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    There is a lot here, so I'll pick a couple.

    A tungsten light bulb is non-linear, but resistive. In fact the resistance is about 10x lower at startup. It's just the Resistance-temp coef of Tungsten.

    DC component.
    You may be missing something. In a push-pull amplifier like audio is usually class A-B. In Class A-B, there is a slight conduction of one of the transistors at all times. That's not the same as offset either, and it's called a DC bias current. When there is no conduction at all, the amp experiences cross over distortion. The Vbe drop of the output transistors vary with temperature and that's the job of the bias regulator.

    DC offset usually results from the lack of matched components. If you have a high current output, transistors are paralleled. When they are paralleled a small emitter resistor is used to equalize the current. The gains of the transistors have to me matched as well.

    I'd still call it crossover distortion or something like "crossover delay" or "crossover time". It is usually a time where both push pull drivers are turned off. I probably would not call it a "DC component".

    High/Low Z
    An ideal voltage source has Zero resistance

    An ideal current source has infinate impeadance.

    Thevinin and Norton's theorems.
    Check them out: http://en.wikipedia.org/wiki/Norton_theorem That's one of them.

    It basically says that a voltage source can be replaced by a current source in parallel with a resistor and a current source can be replace by a voltage source in series with a resistor. These are very important concepts.

    An audio amplifier uses the term "damping factor" to denote a varient of Z. An amp that is designed for 8 ohms with a damping factor >100 has an output Z < 8/100 ohms.

    In other cases the change in V divided by the change in I can be called the output impedance.
     
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Reactive load

    Let's basically define it as having capacitive or inductive components. Formulas exist for dealing with sine waves and reactive loads where both the voltage and current are still sinusoidal, but out of phase. In this case P=V*I*cos(θ). With a resistive load cos(θ) = 1, so we are back to the normal formula.

    A floresent ballast is a very non-linear load. The current is all over the map. A ballast in general is also non-sinusoidal. A switching power supply usually has to incorporate power factor correction because of regulations. Industrial complexes that have a lot of motors will get charged more if their power factor. cos(θ) is high.

    The circulating currents tat your talking about may be "Eddy Currents". See: http://en.wikipedia.org/wiki/Eddy_currents
     
  4. dave

    Dave New Member

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  5. Billy Mayo

    Billy Mayo Member

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    At my work now they call it circulating current when you measure current or voltage on your DVM meter but it's considered Garbage? it's not a real reading because it's circulating current they say

    Which I don't know what they mean, do you?

    You know when you measure a switch when its OFF , but you get garbage voltage or current readings

    They say its garbage readings, which is circulating current
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    How about "phantom voltages"? Newer meters place a 1K load on things to try to avoid that.
     
  7. Billy Mayo

    Billy Mayo Member

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    Well the load box we use at work has a transformer and light bulbs in series with breakers to each light bulb

    When you don't have any breakers turn on

    My Fluke current meter and DVM meter pick up Readings like if they are real readings

    Because of the transformers eddy current and there is a fan running too which picks up the current in the fan also its about 1 amp reading because its not real my boss says its eddy or circulating current he says

    Yes you can call it a " Phantom Measurement" not real voltage or current, its circulating or magnetic eddy currents
     
  8. Billy Mayo

    Billy Mayo Member

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    Another example is: There is multiple breakers on a unit that are AC 120, AC 120, AC 120

    When the Switches are OPEN, My DVM meter will read 65 volts, it should measure zero volts, the 65 volts is just a phantom measurement its not real

    My boss says the 65 volts it not read because its the switch is OPEN there is nothing there it's just circulating current or a magnetic voltage

    Do you know what he means?
     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I'd have to see the schematic to really comment, but aprox 1/2 the supply voltage means something funny is going on. Take this http://www.cor.com/Series/PowerLine/R/ for example. Note the two capacitors to ground. If the ground wa s"lifted", you would find about 1/2 the supply voltage at the ground terminal when measured with a high Z meter. If you put a load on the ground, it will go away. The voltage is being divided by the capacitors reactance. The amount of current is small, but is detected with a high Z meter.

    It's probably an artifact concerning leakage currents present because of a few filters or capacitors to ground.

    The voltages are real. The currents that you can draw from them are really small.

    I had a couple of PHD's trying to figure out why a piece of equipment was sparking. They spent about 16 man-hours over the weekend between them and could not find out what was wrong. When I came in in the morning, I had the problem solved within 5 minutes. The ground had broken away on one of the outlets and therefore the ground on another instrument was the junction of the two caps. Hence 65 V or so between two grounds.

    A really tough problem, but I set u[ system that could measure 2 picoamps (2e-12 Amps) or so, so I'm very familiar with the oddities at these currents and the difficulty measuring stuff. I'm also familiar as to what happens at 100 kV and 0.1 Amps and also 1000 W RF energy into 50 ohms.
     
  10. Billy Mayo

    Billy Mayo Member

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    But DC doesn't have a frequency so how can the voltage be divided by the capacitors reactance?

    Yes you're right, its leakage current

    But that leakage current and leakage voltage gets measured by my DVM meter

    Or the ground is lifted
     
  11. Billy Mayo

    Billy Mayo Member

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    Unless the DC frequency is 60 hz or 50hz because of the AC ripple right? the AC ripple is the 60hz or 50hz?

    The capacitors reactance would have to be set at 60hz or 50hz right?
     
  12. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    You were talking AC, not DC. Nonetheless, this should be a good read: http://www.electro-tech-online.com/custompdfs/2013/04/probes.pdf

    Remember f = 1/(2∏ f R C); Solve for R. But who cares: f, C, and ∏) are all the same so it's a divide by 2 voltage divider.

    We aren't talking ripple here. Ripple on a full wave rectified supply is 2x the mains frequency.
     
  13. Billy Mayo

    Billy Mayo Member

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    oh ok sorry about that

    What are phase lock circuits used for?

    I know the circuit locks phase IN phase together , but why would you need or want that?

    Without a phase lock circuit, it's called free running

    Are Phase Lock Circuits used just to lock the input and output together?

    To test if a phase lock circuit is working, you put oscilloscope channel#1 on the input and oscilloscope channel#2 on the output on a unit

    The problem here for me is that I can only use the Probes Ground on Channel#1 only

    Oscilloscope channel#2 probe doesn't have a ground, so the sine waveform is noisy and moves back and forth very fast some techs call it oscillation or noise

    I set the time base on the oscilloscope so that I can see the phase shift so they are so very close together, that they are in phase

    The problem is that the channel#2 waveform is so noise and moving I can't take a measurement

    I can't use the probe ground on channel#2 because my manager says that it will fry the oscilloscope because there is a DC offset or a potential difference voltage from earth ground, and it will cause a SHORT CIRCUIT

    If a circuit has DC offset on the ground or a potential difference from earth ground, the oscilloscopes ground will SHORT CIRCUIT the DC offset or potential difference

    My manager told me that I can use a DVM meter and measure the input AC HOT line Black wire with the outputs AC HOT line Black wire, It measured 7 volts AC going from input HOT to output HOT. He said this is the phase angles voltage of the inputs sinewave and the outputs sinewave. Next I measured using the DVM meter to the Neutrals White wire from the input to the Neutrals White wire at the output of the unit, it measured 1.4 volts AC. He said this is a phase angle voltage, the phase angle is the inputs waveform and the outputs waveform, the phase shift between the input and output

    I have seen techs use an Ez jumper wire to extend the oscilloscopes probe at the probes tip rather than using it on the ground clip. When you use an Ez Hook jumper wire on the ground clip, it picks up to much noise. But when you use an Ez hook jumper wire on the probes tip and use the Ez hook to measure test points, it doesn't have noise on the signal.

    The Probes ground clip is so short it's so hard to make measurements, So you use an Ez hook on the probes lead instead of extending the probes ground clip

    I'm just confused as why they just don't make a oscilloscope probe that has a longer probe tip
     
  14. Billy Mayo

    Billy Mayo Member

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    Will measuring each IC chips pins impedance lead me to a short?

    When measuring with a DVM meter set to ohms, measuring each IC pin referenced to ground, is this measuring the impendance?

    IC chips either logic TTL , CMOS or op amps

    I'm trying to measure the impedance of each IC pin that is " in circuit" , but what is my reference? when measuring the impedance of an IC pin? the reference should be where?

    Will this lead me to finding a short circuit?

    if there is a short, the impedance or in circuit resistance of the IC pin will change?
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Demodulating FM for one. The 19 kHz Pilot tone has to be converted to a 38 Khz carrier in sync with the 19 Khz, otherwise you would not get stereo.

    PLL's are used a lot to frequency multiply or divide or to sync to a multiple of the frequency for whatever reason.
     
  17. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    In a NORMAL old scope the scope ground is the earth ground. What your setup has I have no idea.

    As long as the signals are referenced to the scopes ground, you should have no trouble seeing them. I suspect a triggering issue and not knowing how to use the scope.

    If both signals are clean by themselves, then I suspect your not triggering properly. If A is your reference, then you should be triggering only on A and using the slope/level controls or an external trigger.

    Auto-trigger is a convienience.
     
  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I'm confused. The 1.4 V is probably 2 diode drops.

    Does anyone know what they are doing?
     
  19. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Unless the signals are very low voltage or have a fast rise time, you really should not need the probe clip. It's always a "good idea" to have your work plugged into an isolation transformer then you can ground without fear of ground loops, etc.

    For low frequencies, the probe is nearly meaningless. You can only compensate a probe that divides. e.g. x10, x100.
    The scope probe is essentially shielded to the tip. Some scope probes come with various attachments.

    I really can't comment on the use of the ground clip without knowing more.
     
  20. Billy Mayo

    Billy Mayo Member

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    It's a UPS AC input 120 , AC output 120

    120 AC out of the outlet from the wall goes into the UPS unit and comes out AC 120 on the output of the UPS unit

    When you measure the inputs HOT on oscilloscope channel#1, outputs HOT is on oscilloscope channel#2, Trigger channel is on channel#1

    Channel#2 has noise because I can't use the oscilloscopes probe ground on the units outputs neutral

    It will short out the DC offset voltage or potential difference DC voltage my manager said, it will cause a short circuit

    The 120 AC outlet from the wall has a earth ground, the Unit has a ground , but these is a potential difference between grounds so the oscilloscope will short it out
     
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I have a hard time believing it's 120 in and 120 out, because you have just said it's 7+-1.2 V

    Now, I would believe that the waveform of the input an the waveform of the output are drastically different.

    I'd also believe that your NOT using a TRMS meter to measure both waveforms.

    I also don't know the topology of the UPS: Always ON or transfer to battery.

    The input is likely a sine wave and the output is a modified sine wave.

    What's a modified sine wave? The sine wave is synthesized with a few pulses and then the resultant waveform is run through a 60 Hz filter to clean up the edges.

    You would probably get better agreement using a TRMS meter.

    I'll bet dollars to donuts that the reason for the discrepancy is the waveform of the input and output AND the type of meter used.
     

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