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Re: ESR Meter - Roll your own - ESRrev0.JPG

Discussion in 'Electronic Design' started by Mike Monett, Jul 9, 2007.

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  1. Mike Monett

    Mike Monett Guest

    Hi John,

    Do you mind if I make some comments? The 1 ohm resistor, R5, can be
    removed from the circuit. It is at a virtual ground node and has
    little or no voltage across it. So removing it has little effect on
    the circuit.

    With R5 gone, and the ESR range switch in the 1 ohm position, the
    180 ohm resistor, R4, is effectively in series with the capacitor
    under test. The op amp merely changes the location of the ground
    node, and inverts the output signal polarity.

    Since R4 (180 ohms) is now in series with the capacitor, it
    completely swamps out the internal ESR (0.05 ohms.) This means the
    series combination of C, L, and R has negligible "Q", and there is
    no quadrature or orthogonal component in the circuit.

    However, as the ESR decreases, the corresponding voltage drop that
    we are trying to measure also decreases. We no are faced with the
    problem that the di/dt from the inductor is much larger than the I*R
    drop from the ESR. This means the leading and trailing edge of the
    square wave have large spikes.

    If you used a diode peak detector to measure the amplitude, it would
    respond as best it could to the leading edge spike, which would make
    it impossible to measure the drop across the ESR. Your circuit and
    Larkin's share this problem.

    Using a synchronous rectifier helps a bit, but you are now faced
    with trying to turn it on after the leading edge spike, and to turn
    it off before the trailing edge spike. That could be tricky.

    I spent this afternoon looking at these problems in SPICE, and have
    come to an amazing observation. There is a hidden but very
    significant feature in the bridge ESR circuit referred to at the
    beginning of this thread. The links are:

    1. Talino Tribuzio's page, showing the circuit from Nuova
    Elettronica:

    http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/index.htm

    2. Gintaras' web page, who refers to Tribuzio's page in his readme

    http://alytus.auksa.lt/esr/

    The schematic is at

    http://alytus.auksa.lt/esr/esr_meter_schematic.pdf

    The valuable hidden feature is the bridge configuration completely
    eliminates the leading and trailing edge spikes due to the capacitor
    internal inductance. Since the spikes are in phase with the square
    wave signal on the other side of the bridge, they simply disappear
    at the output of the op amp!

    This means the peak detector has a very clean square wave to work
    with, and it can give a much more accurate measurement of the
    signal. There is no tricky timing to fiddle with that can go out of
    whack just when you need to use the tester.

    If you like, I can post the analysis of your circuit and Larkin's
    version showing the huge spikes that appear as the ESR becomes
    smaller, and the triangular wave from the capacitance charging and
    discharging. I don't really see a good way of overcoming these
    problems.

    As I mentioned in previous posts, the bridge circuit has significant
    advantages, including low test voltage, in-circuit test, shorted
    capacitor detect, etc. With the extremely clean output signal into
    the peak detector, it becomes the obvious choice for hassle-free ESR
    measurements.

    I'll post the LTspice ASC file here along with the PLT file so you
    can see how it works. I changed the bridge resistance to lower
    values to allow measuring lower values of ESR.

    Here's the LTspice ASC file:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Version 4
    SHEET 1 880 708
    WIRE -496 -112 -528 -112
    WIRE -368 -112 -416 -112
    WIRE -304 -112 -368 -112
    WIRE -192 -112 -224 -112
    WIRE -368 -96 -368 -112
    WIRE -128 -80 -160 -80
    WIRE -48 -64 -64 -64
    WIRE -720 -48 -816 -48
    WIRE -704 -48 -720 -48
    WIRE -592 -48 -624 -48
    WIRE -528 -48 -528 -112
    WIRE -528 -48 -592 -48
    WIRE -368 -48 -528 -48
    WIRE -192 -48 -192 -112
    WIRE -192 -48 -288 -48
    WIRE -128 -48 -192 -48
    WIRE -816 -32 -816 -48
    WIRE -160 0 -160 -80
    WIRE -160 0 -240 0
    WIRE 128 16 96 16
    WIRE 224 32 192 32
    WIRE 240 32 224 32
    WIRE 336 32 304 32
    WIRE -528 48 -592 48
    WIRE -240 48 -240 0
    WIRE -240 48 -448 48
    WIRE -224 48 -240 48
    WIRE -96 48 -144 48
    WIRE -48 48 -48 -64
    WIRE -48 48 -96 48
    WIRE 32 48 16 48
    WIRE 128 48 32 48
    WIRE -816 64 -816 48
    WIRE 32 128 32 48
    WIRE -720 144 -720 -48
    WIRE -704 144 -720 144
    WIRE -592 144 -592 48
    WIRE -592 144 -624 144
    WIRE -512 144 -592 144
    WIRE -416 144 -448 144
    WIRE -304 144 -336 144
    WIRE -192 144 -224 144
    WIRE -592 160 -592 144
    WIRE -192 160 -192 144
    WIRE 96 176 96 16
    WIRE 208 176 96 176
    WIRE 336 176 336 32
    WIRE 336 176 208 176
    WIRE 208 192 208 176
    WIRE 336 208 336 176
    WIRE 32 224 32 208
    WIRE -592 256 -592 240
    WIRE -464 272 -480 272
    WIRE -432 272 -464 272
    WIRE -272 272 -288 272
    WIRE -240 272 -272 272
    WIRE -480 288 -480 272
    WIRE -288 288 -288 272
    WIRE 208 288 208 272
    WIRE 336 288 336 272
    WIRE -480 384 -480 368
    WIRE -288 384 -288 368
    FLAG -96 48 DIFF
    FLAG -592 256 0
    FLAG -192 160 0
    FLAG -816 64 0
    FLAG -368 -96 0
    FLAG -592 -48 E2P
    FLAG -592 48 E2N
    FLAG 32 224 0
    FLAG 336 288 0
    FLAG 208 288 0
    FLAG 336 32 DC
    FLAG -480 384 0
    FLAG -464 272 VCC
    FLAG -288 384 0
    FLAG -272 272 VEE
    FLAG 224 32 VOP
    FLAG 32 48 VIN
    FLAG 160 0 VCC
    FLAG 160 64 VEE
    FLAG -96 -96 VCC
    FLAG -96 -32 VEE
    SYMBOL res -608 144 R0
    SYMATTR InstName R8
    SYMATTR Value {Rb}
    SYMBOL res -608 128 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R9
    SYMATTR Value {Rt}
    SYMBOL cap -448 128 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C3
    SYMATTR Value {C}
    SYMBOL res -320 128 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R10
    SYMATTR Value {ERS}
    SYMBOL ind -320 160 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 5 56 VBottom 0
    SYMATTR InstName L3
    SYMATTR Value {L}
    SYMBOL Voltage -816 -48 R0
    WINDOW 0 42 44 Left 0
    WINDOW 3 -22 -62 Left 0
    WINDOW 123 15 130 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value PULSE(0 4 0 {Tr} {Tr} 5u 10u)
    SYMBOL res -608 -64 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R5
    SYMATTR Value {Rt}
    SYMBOL res -512 -96 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 0 56 VBottom 0
    SYMATTR InstName R11
    SYMATTR Value {Rb}
    SYMBOL res -320 -96 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 0 56 VBottom 0
    SYMATTR InstName R12
    SYMATTR Value 47k
    SYMBOL res -384 -32 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 0 56 VBottom 0
    SYMATTR InstName R13
    SYMATTR Value 1k
    SYMBOL res -544 64 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 0 56 VBottom 0
    SYMATTR InstName R14
    SYMATTR Value 1k
    SYMBOL res -240 64 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 0 56 VBottom 0
    SYMATTR InstName R15
    SYMATTR Value 47k
    SYMBOL cap 16 32 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C4
    SYMATTR Value 2n
    SYMBOL res 16 112 R0
    SYMATTR InstName R16
    SYMATTR Value 47k
    SYMBOL diode 240 48 R270
    WINDOW 0 32 32 VTop 0
    WINDOW 3 0 32 VBottom 0
    SYMATTR InstName D1
    SYMATTR Value 1N4148
    SYMBOL cap 320 208 R0
    SYMATTR InstName C5
    SYMATTR Value 2nf
    SYMBOL res 192 176 R0
    SYMATTR InstName R17
    SYMATTR Value 470k
    SYMBOL Opamps\\1pole 160 32 R0
    SYMATTR InstName U1
    SYMATTR Value2 Avol=1Meg GBW=100Meg Slew=100Meg
    SYMBOL Voltage -480 272 R0
    WINDOW 0 42 44 Left 0
    WINDOW 3 47 72 Left 0
    WINDOW 123 15 130 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value 10
    SYMBOL Voltage -288 384 R180
    WINDOW 0 42 44 Left 0
    WINDOW 3 47 72 Left 0
    WINDOW 123 15 130 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V3
    SYMATTR Value 10
    SYMBOL Opamps\\1pole -96 -64 R0
    SYMATTR InstName U2
    SYMATTR Value2 Avol=1Meg GBW=100Meg Slew=100Meg
    TEXT -528 -224 Left 0 ;'Tribuzio Bridge ESR Circuit
    TEXT -528 -184 Left 0 !.tran 0 2.2m 2m 100n
    TEXT 32 -200 Left 0 !.param C = 100uF\n.param L = 2.533E-08\n.param ERS =
    0.00005\n.param Rt = 100\n.param Rb = 1\n.param Tr = 100n

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Here's the PLT file:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    [Transient Analysis]
    {
    Npanes: 3
    Active Pane: 1
    {
    traces: 1 {268959746,0,"V(dc)"}
    X: ('µ',0,0,2e-005,0.0002)
    Y[0]: (' ',3,0,0.003,1)
    Y[1]: ('_',0,1e+308,0,-1e+308)
    Volts: (' ',0,0,0,0,0.003,1)
    Log: 0 0 0
    GridStyle: 1
    },
    {
    traces: 1 {268959747,0,"V(diff)"}
    X: ('µ',0,0,2e-005,0.0002)
    Y[0]: (' ',1,-1,0.2,1)
    Y[1]: ('_',0,1e+308,0,-1e+308)
    Volts: (' ',0,0,2,-1,0.2,1)
    Log: 0 0 0
    GridStyle: 1
    },
    {
    traces: 1 {268959748,0,"V(e2n)"}
    X: ('µ',0,0,2e-005,0.0002)
    Y[0]: ('m',0,0,0.002,0.04)
    Y[1]: ('_',0,1e+308,0,-1e+308)
    Volts: ('m',0,0,0,0,0.002,0.04)
    Log: 0 0 0
    GridStyle: 1
    }
    }

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Regards,

    Mike Monett
     
  2. Mike Monett

    Mike Monett Guest

    To complete the record, here is the LTspice files for John J. and
    John L.'s ESR measuring circuits. The capacitor parameters are
    chosen to resonate at 100KHz, which is also the test frequency.

    As can be seen in the transient analysis, there is no evidence of
    orthogonal or quadrature components in the output signal.

    The reason is the external circuit resistance completely swamps the
    internal ESR. The external circuit determines the current through
    the series network, so there is no energy transferred back and forth
    between the capacitive and inductive components, thus no phase shift
    between them.

    The output signal is simply the di/dt from the ESL, I*dt from the
    capacitor, and I*ESR, which is what we are trying to measure. Both
    approaches give almost identical results.

    You can change the component values in the .param list. As can be
    seen, the inductive spike is very sensitive to risetime. Trying to
    measure ESR below about 50 milliohms becomes very problematic with
    these approaches.

    As shown in the parent post, the bridge approach removes the
    inductive spike, but it leaves the capacitor charging ramp. So it
    also begins to fail below about 50 milliohms ESR.

    However, the bridge approach allows in-circuit testing,
    automatically detects shorted capacitors, and is insensitive to the
    polarity of the capacitor.

    Here is the LTspice ASC file:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Version 4
    SHEET 1 880 708
    WIRE -64 -48 -592 -48
    WIRE -32 -48 -64 -48
    WIRE -736 16 -800 16
    WIRE -592 16 -592 -48
    WIRE -592 16 -656 16
    WIRE -544 16 -592 16
    WIRE -448 16 -480 16
    WIRE -336 16 -368 16
    WIRE -224 16 -256 16
    WIRE -800 32 -800 16
    WIRE -224 32 -224 16
    WIRE -800 128 -800 112
    WIRE -688 304 -800 304
    WIRE -576 304 -608 304
    WIRE -544 304 -576 304
    WIRE -512 304 -544 304
    WIRE -496 304 -512 304
    WIRE -400 304 -432 304
    WIRE -288 304 -320 304
    WIRE -176 304 -208 304
    WIRE -64 304 -176 304
    WIRE -32 304 -64 304
    WIRE -576 320 -576 304
    WIRE -512 384 -512 304
    WIRE -480 384 -512 384
    WIRE -352 384 -400 384
    WIRE -176 384 -176 304
    WIRE -176 384 -352 384
    WIRE -800 400 -800 384
    WIRE -352 400 -352 384
    WIRE -576 416 -576 400
    WIRE -400 416 -416 416
    WIRE -416 432 -416 416
    WIRE -512 464 -512 384
    WIRE -400 464 -512 464
    WIRE -352 496 -352 480
    FLAG -800 400 0
    FLAG -64 304 Jardine
    FLAG -576 416 0
    FLAG -416 432 0
    FLAG -352 496 0
    FLAG -64 -48 Larkin
    FLAG -224 32 0
    FLAG -800 128 0
    FLAG -544 304 Vin
    SYMBOL res -592 304 R0
    SYMATTR InstName R2
    SYMATTR Value 1e6
    SYMBOL res -592 288 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R3
    SYMATTR Value 180
    SYMBOL Voltage -800 288 R0
    WINDOW 0 42 44 Left 0
    WINDOW 3 -41 151 Left 0
    WINDOW 123 15 130 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value PULSE(4 -4 0 {Tr} {Tr} 5u 10u)
    SYMBOL cap -432 288 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C1
    SYMATTR Value {C}
    SYMBOL res -304 288 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R1
    SYMATTR Value {ESR}
    SYMBOL ind -304 320 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 5 56 VBottom 0
    SYMATTR InstName L1
    SYMATTR Value {L}
    SYMBOL E -352 384 R0
    WINDOW 0 38 42 Left 0
    WINDOW 3 36 69 Left 0
    SYMATTR InstName E1
    SYMATTR Value 1e5
    SYMBOL res -384 368 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R4
    SYMATTR Value 100
    SYMBOL res -640 0 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R6
    SYMATTR Value 180
    SYMBOL cap -480 0 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C2
    SYMATTR Value {C}
    SYMBOL res -352 0 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R7
    SYMATTR Value {ESR}
    SYMBOL ind -352 32 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 5 56 VBottom 0
    SYMATTR InstName L2
    SYMATTR Value {L}
    SYMBOL Voltage -800 16 R0
    WINDOW 0 42 44 Left 0
    WINDOW 3 21 103 Left 0
    WINDOW 123 15 130 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value PULSE(0 4 0 {Tr} {Tr} 5u 10u)
    TEXT -528 -208 Left 0 ;'ESR Measuring Circuits
    TEXT -856 -152 Left 0 !.param C = 100uF\n.param L = 2.5330295910584E-
    08\n.param ESR = 0.05\n.param Tr = 100n
    TEXT -816 192 Left 0 ;NOTE:\nR2 was 1 ohm in the original. It is at
    virtual ground and has little effect on the circuit. \nR4 was 56k in the
    original. Reduced to 100 ohm to reduce settling time for transient
    analysis.
    TEXT -856 -184 Left 0 !.tran 0 100.1m 100m 250n

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Here is the PLT file:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    [Transient Analysis]
    {
    Npanes: 2
    {
    traces: 1 {524292,0,"V(jardine)"}
    X: ('µ',0,0,1e-005,9.99998048950707e-005)
    Y[0]: ('m',0,0.03,0.002,0.058)
    Y[1]: ('_',0,1e+308,0,-1e+308)
    Volts: ('m',0,0,0,0.03,0.002,0.058)
    Log: 0 0 0
    GridStyle: 1
    },
    {
    traces: 1 {524290,0,"V(larkin)"}
    X: ('µ',0,0,1e-005,9.99998048950707e-005)
    Y[0]: (' ',3,2.025,0.001,2.039)
    Y[1]: ('_',0,1e+308,0,-1e+308)
    Volts: (' ',0,0,3,2.025,0.001,2.039)
    Log: 0 0 0
    GridStyle: 1
    }
    }
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Regards,

    Mike Monett
     
  3. john jardine

    john jardine Guest

    [my pleasure Mike :] The 1 ohm resistor, R5, can be
    Can't lose the 1 ohm as the other ranges need it. If you look at the feed
    current you'll notice with the 1 ohm either in or out, the current to the
    virtual earth is the same at 20ma. So the 4V signal, 180 ohms has the
    same drive effect as 20mV, 1 ohm. Switch and wiring hence kept simple.
    I'm puzzled. The 180 ohm sees only 0V (the V.E.). The capacitor sees
    similarly. Currents essentially isolated. Phase changes notified by opamp
    output voltage.
    For some reason LTspice is refusing your .asc text list, so I can't picture
    where that 'L' and 180 ohms are. Can you repost it as a pic' somehow?.
    I had a play with my unit and it is sensitive to (a lot) of added series
    inductance. There's a 5% reading change with 2 foot of coiled test leads
    (about 200nH). This is basically a 'ring down' (70MHz) at the opamp output
    and seems related to the opamp stability (the THS is something like 150MHz
    GB).
    On the 1 ohm range it is surprisingly difficult to add noticable test
    inductance without adding serious amounts of lead/wire resistance.
    Essentially the meter is reading lead resistance with a bit of
    capacitor ESR thrown in.
    [Poly cap and s/c link. actual Vout -.063V. Link replaced with 1206 0.01ohms
    and Vout=0.052V].
    As test I've looked for inductive 'spikes' using the 'scope and about 20
    different test capacitors (good through to rubbish). I saw nothing
    untowards.
    Presumably confirming that capacitors are not inductive (other than the
    trivial effect of their leads and the test socket wiring).
    The test spikes I forced were a transient effect and only occupied a few %
    of each complete cycle. Yes, a peak detector (without windowing) would have
    severe problems on such a waveform. The niceness of the PSR is that it
    can take on allcomers and average the spike energy out over each full
    cycle.
    It's not exact, as there's a 15% reading error with Qs up at 2.5. The opamp
    clips at Q=3 but these are good quality poly' capacitors.
    Luxury!. I had a bad cap' problem. Result was a ESR meter. Cost me a day to
    design and build. I've only used the damned thing once in the past year :)

    and have
     
  4. [ snip ]

    John, wrt the alytus.auksa.lt schematic -- I don't see exactly
    how it can work. Considering its complete symmetry: two 22-ohm
    resistors to ground and 4.5mA square-wave drive, identically on
    each D.U.T. pin, there can be no current through the capacitor.
    Are we looking at the same drawing?
     
  5. Mike Monett

    Mike Monett Guest

    Win,

    If you are referring to http://alytus.auksa.lt/esr/esr_meter_schematic.pdf,
    the right side of the capacitor, the CAP2 pin on J6, goes to ground, and
    not to the junction of R12 (1K) and R17 (22).

    The left side of the cap is connected to the left side of the bridge, at
    the junction of R11 (1K) and R16 (22).

    There seems to be an optical illusion that makes you believe the cap is
    connected across the bridge, and I made the same mistake the first time I
    looked at it. But of course, it wouldn't work if it was connected that way.

    The cap really is connected from the left side of the bridge to ground.

    Regards,

    Mike Monett
     
  6. Thanks, now I can see again! Praise the Lord!
     
  7. Mike Monett

    Mike Monett Guest

    He is busy on other things, but asked me to thank you for the kind
    thought:)

    Regards,

    Mike Monett
     
  8. Winfield

    Winfield Guest

    iz7ath says the esr tester circuit came from an Italian magazine,
    Nuova Elettronica N212. It would be interesting to see their
    writeup, because its operation seems backwards to me. If no
    capacitor is connected, the bridge is balanced, and there's no
    signal to the meter, which reads 0. With a capacitor connected
    the bridge becomes unbalanced. A perfect capacitor, esr = 0 ohms,
    maximally unbalances the bridge, and presumably pushes the meter
    to full scale. A poor capacitor reads slightly less than full
    scale. For example, with esr = 1 ohm (which is not a very good
    capacitor by today's standards) we still get a nearly full-scale
    meter reading, because 1 ohm is so much less than 22 ohms, and
    is still pretty close to zero ohms by comparison. So the meter
    is hard to read, showing little change for various capacitor esr
    values in the sub-1-ohm region of interest. In fact, 1-ohm and
    0.1 ohm capacitors would have nearly the same reading. Not good!
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Looks like there will be lots of SR error too. It appears that the ideal
    transfer function at the output will be a peak of ~Vcc*(1-ESR/22) which
    is not too bad, it can be worked but he needs to change some things
    around...such as subtracting the voltage at the junction of R11/12.
     
  10. Mike

    Mike Guest

    The same meter was published by Marvin Smith in the July 2001 edition of Poptronics.
    A quick google search found many references to the Poptronics article, but no copy of it.
    I know it's the same meter since I have a PDF copy of the Poptronics article.

    Mike



    When truth is absent politics will fill the gap.
     
  11. Winfield

    Winfield Guest

    We'd love to see a copy of the article. Failing that, a posting
    of the relevant portion of the meter-reading interpretation and
    of the circuit-operation explanation would be helpful. Be sure
    to include the author's full names for credit.
     
  12. The Phantom

    The Phantom Guest

    SNIP
    Over on ABSE, Mike posted what appears to be a bad English translation of
    some of the article:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The project came from an italian magazine (Nuova Elettronica N212);

    It's very simple but interesting; I've built it and tested some
    capacitors, so I think it's very useful: build it; It measures the
    ESR (Equivalent Serie Resistance) of capacitor (electrolytic and
    not); pratically you can see if a capacitor is good or not.

    It's a bridge circuit that work at 100Khz; there're the following
    possibilities:

    1) The electrolytic capacitor is good: (low ESR) the bridge will
    stay balanced and the meter will indicate the maximun current.

    2) The electrolytic capacitor is not good: (high ESR) the bridge
    will be unbalanced and that will cause the meter to indicate less
    current; as less the meter will indicate as higher will be the ESR;
    After few measure you'll be able to decide if a capacitor is good or
    not.

    3) There is a short circuit in the electrolytic capacitor: the meter
    will indicate the maximum current and the red LED will lamp;
    capacitor is not good.

    4) The electrolytic capacitor is broken: the meter will not move.
    Capacitor is not good.

    http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/index.htm

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    It's interesting how the author calls the case where a perfect capacitor
    is connected, "balanced".
     
  13. Mike

    Mike Guest

    Ok, I posted the article on a.b.s.e along with a link to a totally different meter that was sold by Dick Smith
    electronics. I'd be interested to hear any comments on the Dick Smith version.

    Mike



    If there is no absolute truth then nothing can be known.
     
  14. DaveM

    DaveM Guest


    The DSE meter was designed by Bob Parker, an aussie with a good head on his
    shoulders. The meter has been marketed as both a kit (best bang for the buck)
    and fully assembled and tested models. Most service techs that I know and those
    that have posted on the sci.electronics.repair NG swear by this meter.
    I bought and built a kit a number of years ago, and still use it. It's paid for
    itself many times over in the time that I've owned it.

    I understand the Dick Smith has stopped selling the meter, but Bob has found
    other outlets for it. John's Jukes (http://www.flippers.com/) in Canada sells
    them (that's where I bought my copy).

    I don't think you'll find a bad note from anyone about this meter.

    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
    address)

    "In theory, there isn't any difference between theory and practice. In
    practice, there is." - Yogi Berra
     
  15. Winfield

    Winfield Guest

    I'd love to have one of those meters. The design seems respectable,
    and the most sensitive range, 0.00 to 0.99 ohms, looks ideal for
    working with serious switching-supply capacitors. I see it uses a
    50mA test current and amplifies the resulting esr signal by about
    25x before presenting it to a comparator, the other side of which
    gets a slow 20V/ms ramp (9.5uA and 470nF), to measure the signal.

    The difference between Bob Parker's design for Dick Smith Elec.,
    and the Marvin Smith esr meter we were discussing is dramatic.
     
  16. Winfield

    Winfield Guest

    From Mike's abse post, with the DSE / Bob Parker link:

    There is another meter kit that was available from
    Dick Smith Electronics. The manual can be found at
    http://mainelectronics.com/pdf/k7204inst.pdf
     
  17. The Phantom

    The Phantom Guest

    See more about the Bob Parker meter here:
    http://members.ozemail.com.au/~bobpar/esrmeter.htm

    Get the .pdf for the latest model here:
    http://members.ozemail.com.au/~bobpar/k7214.pdf

    Go have a look at a forum all about bad caps here:
    http://www.badcaps.net/

    I've only just started looking around there, and there's a lot about ESR.
    For example:
    http://www.badcaps.net/forum/showthread.php?s=01febe89f8a9b210661a6ca2498e21d8&p=32706#post32706
     
  18. Fred Bloggs

    Fred Bloggs Guest

    9.5u/470n=20V/ms??? Something's not right there. And the ESR pulse
    amplifier DC bias schematic seems screwed with about 0.6V output offset.
     
  19. Winfield

    Winfield Guest

    Excuse me, I meant to write 20mV/ms. Yes I saw the schematic said
    0.6 volts quiescent at the amplifier output, but I calculated about
    2.8 volts (5*220/320 - 0.65), so that's a puzzle. Moreover, it's a
    non-inverting amplifier, and with low duty-cycle 50mA pulses (for
    low battery consumption), we'd expect positive-going output signal
    pulses from the amplifier. Something indeed looks wrong there.
     
  20. The Phantom

    The Phantom Guest

    Winfield,

    You still have an HP4194, don't you?

    Try doing a sweep of capacitance and ESR from 60 Hz to 1 MHz of some caps
    from a defective mother board. I visited my local computer repair guy and
    he gave me a couple of defective boards destined for recycling.

    Especially sweep some of the really small, high capacity, low voltage
    caps. I saw some unusual characteristics with the physically small caps.

    Some of the ones I tried had self-resonance at 100 kHz.
     
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