Extech tutorial

[Achiles]

I´ve read alot things about the use of extech and some of them makes me confused.
can somone please post some kind of extech tutotial ?
Some kind of "Pickup datasheet log" or "Pickup autopsy datalog" would be nice.

[salvarsan]

Press ON
Toggle parallel mode by pressing PAL/SER until display says "PAL"
Select inductance mode by pressing L/C/R until display says "H" in lower right corner
Select AC resistance mode by pressing Q/D/R until display shows an omega in upper right corner
Toggle test frequency between 120 Hz and 1000 Hz as desired (test at both frequencies).
Connect leads to a coil.

The Extech 380193 User Manual is attached.

[David King]

I think Belwar posted a lot of Extech readings in some posts a few years back. Mr Candy I think may also have posted something along those lines last year as well.

[Achiles]

Tanx David,Salvarsan should i read C/R after L to?
Lets say we are measuring a HB umbalanced coil,
is it a good idea to measure both coils individually?
I just start to playing and that is the way i´m doing it.

[Mike Sulzer]

Tanx David,Salvarsan should i read C/R after L to?
Lets say we are measuring a HB umbalanced coil,
is it a good idea to measure both coils individually?
I just start to playing and that is the way i´m doing it.

You cannot measure the capacitance of a pickup coil because the inductance dominates. The inductance of humbucker coil is best measured at 120 Hz rather than 1000 Hz because of eddy current losses that make errors in the measurement at the higher frequency frequency. At 1000 Hz, the pickup circuit is an inductor with a series resistor, the coil resistance, with a series resistor and inductor in parallel. The last part is a reasonably accurate representation of the effect of the eddy currents. The Extech can handle either a series loss, as used with the pickup coil at 120 HZ, or a parallel loss, but it cannot handle a circuit with both. At 120 Hz, the parallel loss is small, and so you can get a good reading of the inductance in the series mode.

[FunkyKikuchiyo]

There was a spreadsheet online of a whole mess of data collected on pickups that is really handy to reference when you have an LCR meter handy. The original data wasn't collected with an Extech, but it isn't far off. I really like it because the pickups they measure are common ones and make for good comparisons. I'd link it, but all I'm finding are dead links, sorry...

[ScottA]

You cannot measure the capacitance of a pickup coil because the inductance dominates. The inductance of humbucker coil is best measured at 120 Hz rather than 1000 Hz because of eddy current losses that make errors in the measurement at the higher frequency frequency. At 1000 Hz, the pickup circuit is an inductor with a series resistor, the coil resistance, with a series resistor and inductor in parallel. The last part is a reasonably accurate representation of the effect of the eddy currents. The Extech can handle either a series loss, as used with the pickup coil at 120 HZ, or a parallel loss, but it cannot handle a circuit with both. At 120 Hz, the parallel loss is small, and so you can get a good reading of the inductance in the series mode.

In practice, I generally see pretty good agreement between the inductance at 120 and 1000 Hz in the series mode with the Extech, at least below about 10 H.

For example, the stuff I've been looking at the last couple of days represents an inductance range of about 4-8 H. For 1 measurement each of 25 different configurations, forcing the fit through the origin, I get:

H_1000Hz = 1.0003 x H_120Hz

with an R² of 0.9999.

Although the configurations in this particular dataset would be less influenced by eddy current effects and also have relatively high resonant frequencies. Looking at a larger range of data, I would say that as eddy current effects increase, the 1000 Hz measurement starts to diverge a bit, but still is usually within 5% or so.

[jmaf]

Achiles, I found the Extech manual here, will get it to you soon - but it's not really useful, Salvarsan and others have provided more info than it's in it.

Not wanting to hijack Achiles' thread, (I think he may have similar questions?), if anyone could please help out:

1) When reading a capacitor, the R that appears on the secondary reading is different than if you test the capacitor via the main R function. Why? (Same frequency.)

2) About question 1, when measuring R for a capacitor, is that the ESR?

3) The Q factor should be reactance divided by DCR, correct? The higher the Q, the more reactance to resistance ratio, right? Good pickups have high reactance, low DC resistance?

4) Raising the frequency from 120 to 1K seems to multiply Q, but not by 8.3, what ratio is Q increasing when we increase the frequency 8.3 times from 120 to 1k?

5) If I take a function and test something unexpected with it, are the readings valid? Testing inductance in a guitar cable for example? Capacitance in a coil? Or will the inductive reactance in a iron core coil for example ruin the capacitance reading in all cases like Mike Sulzer explained? If I read some inductance on a resistor, is that reading correct?

Thanks in advance for any pointers.

[Mike Sulzer]

Scott, your measurements show how good the Extech meter is. Measuring inductance when the inductive reactance is low (low frequency, therefore low Q) is not so easy. One reason often given for using the higher frequency is to avoid just such inaccuracy. But it is not necessary to do that.

In practice, I generally see pretty good agreement between the inductance at 120 and 1000 Hz in the series mode with the Extech, at least below about 10 H.

For example, the stuff I've been looking at the last couple of days represents an inductance range of about 4-8 H. For 1 measurement each of 25 different configurations, forcing the fit through the origin, I get:

H_1000Hz = 1.0003 x H_120Hz

with an R² of 0.9999.

Although the configurations in this particular dataset would be less influenced by eddy current effects and also have relatively high resonant frequencies. Looking at a larger range of data, I would say that as eddy current effects increase, the 1000 Hz measurement starts to diverge a bit, but still is usually within 5% or so.

[Mike Sulzer]

1, 2. Yes, if you have resistance in series with the "ideal" capacitance, you cannot measure that at dc since the impedance of the capacitor is infininte. So the effects of ESR are frequency dependent.

3. The Qs of pickups vary, depending on the required sound. It will not sound good if you make it too high.

4. Depending on the pickup core design, the effects of eddy currents will vary. These effects are frequency dependent and affect the Q reading.

5. Usually the inductive reactance of a resistor is so low compared to the resistive that even the Extech cannot read it with good accuracy. Knowing when to trust that kind of measurement is not so easy.

Achiles, I found the Extech manual here, will get it to you soon - but it's not really useful, Salvarsan and others have provided more info than it's in it.

Not wanting to hijack Achiles' thread, (I think he may have similar questions?), if anyone could please help out:

1) When reading a capacitor, the R that appears on the secondary reading is different than if you test the capacitor via the main R function. Why? (Same frequency.)

2) About question 1, when measuring R for a capacitor, is that the ESR?

3) The Q factor should be reactance divided by DCR, correct? The higher the Q, the more reactance to resistance ratio, right? Good pickups have high reactance, low DC resistance?

4) Raising the frequency from 120 to 1K seems to multiply Q, but not by 8.3, what ratio is Q increasing when we increase the frequency 8.3 times from 120 to 1k?

5) If I take a function and test something unexpected with it, are the readings valid? Testing inductance in a guitar cable for example? Capacitance in a coil? Or will the inductive reactance in a iron core coil for example ruin the capacitance reading in all cases like Mike Sulzer explained? If I read some inductance on a resistor, is that reading correct?

Thanks in advance for any pointers.

[salvarsan]

Tanx David,Salvarsan should i read C/R after L to?
Lets say we are measuring a HB umbalanced coil,
is it a good idea to measure both coils individually?
I just start to playing and that is the way i´m doing it.

If it's unbalanced, YES, measure both individually. Good quality control that way.

The 1kHz vs. 120 Hz AC resistance difference tells you about the eddy current contributions. They let you know more about how consistent your pickup building is.

[Mike Sulzer]

Let's look at a coil that is a bit different from the usual pickup coil as an example of how to use the Extech and understand the results.

The coil in question is intended as an individual string pickup. It uses a humbucker slug as a core and a bobin intended for use swith an EP-13 ferrite core. It is necessary to ream it out slightly for use with the slug. I wind 2,000 turns of #43 wire onto it. With no core, at 120 Hz in series mode, I measure 17.02 mH with a resistance of 322.6 ohms, although this varies with time as the temperature changes. This is a Q of about .04, which is quite low, and so it would not be surprising if this is not too accurate. At 1 KHz I measure 16.69 MH with a Q of about .33. The inductance measurement has changed by about 2%, and since there are no eddy currents, this is probably the result of the low Q at 120 Hz. But even so, this is a pretty small error!

When the core is inserted, the inductance rises to 70.15 MH, 120 Hz, series mode, about four times greater. (The relative increase in a normal pickup coil is somewhat less since the cores do not entirely fill the available space.) I measured 320.2 ohms at this time; my multimeter gave 320.6, closer that I have any right to expect, but a good indication that at 120 Hz, the dominant loss in the coil is the series resistance. At 1000 Hz, the inductance drops by 6.5% and the resistance rises to 365.6 ohms. Why? Well, the short answer is eddy currents, but how does this happen?

The Extech can be thought of as measuring an amplitude and a phase. Or you can think of it as the projections onto the x and y axes, the real and imaginary parts. The interpretation of this measurement is a function of the meter settings, and the assumption is that you have a reactance, either an L or a C with a resistor in either series or parallel. You cannot analyze both at once. The eddy current load goes in parallel with the inductance, and so this is in conflict with the series resistance of the coil. Also the parallel load is not a pure resistance, but has an inductance in series. So the effect of the eddy currents is to reduce the magnitude of the measured impedance and reduce the angle, that is, move it in the directino of the real axis. This will certainly reduce the measured inductance, and probably increase the measured resistance. This rells you something about the eddy current loss. But it does not allow you to compute the value of the parallel impedance. That would require additional measurements.

[Joe Gwinn]

...Also the parallel load is not a pure resistance, but has an inductance in series. So the effect of the eddy currents is to reduce the magnitude of the measured impedance and reduce the angle, that is, move it in the directino of the real axis. This will certainly reduce the measured inductance, and probably increase the measured resistance. This rells you something about the eddy current loss. But it does not allow you to compute the value of the parallel impedance. That would require additional measurements.

The Extech makes one measurement, of complex impedance, and then mathematically fits that impedance to the circuit implied by the selected SER or PAR circuits, so one can deduce one from the other.

The reason to use 1000 Hz is simply that it's in the audio range, and is the standard test frequency for audio. The KHz range is important even if the fundamental is 100 Hz, because what matters are the harmonics in the kilohertz range.

[Mike Sulzer]

The reason to use 1000 Hz is simply that it's in the audio range, and is the standard test frequency for audio. The KHz range is important even if the fundamental is 100 Hz, because what matters are the harmonics in the kilohertz range.

No, that is not the reason, not even close. You are completely ignoring the context within which the measurement occurs.

For example, consider the measurement of a resistor. The context here is that although all resistors have inductance and capacitance as well as resistance, a measurement made at dc is all you need in most cases for audio. Sometimes you need more, but usually your multimeter tells you all you need to know.

The context of pickup coil measurement is much more complicated. It can only be determined by making measurements over the whole useful frequency range of such devices and constructing a model containing the essential components. The result of this model is the knowledge that the Extech measurement at 120 Hz yields the inductance of the coil and its series resistance to good accuracy. The measurement at 1000 Hz adds some information about the degree of eddy current loss, determined by how much it deviates from the 120 Hz measurement.

It appears that you do not agree with this. You can give some beef to this disagreement by making measurements
and analyzing the results in order to show that your understanding, whatever it might be, is correct. However, I am confident that if you put in the work and think about it correctly, you will come to agree with my understanding.

[RedHouse]

Aw geez, here we go again!