Extech tutorial

[Joe Gwinn]

You asked why people measure audio components at 1 KHz, and I answered. You replied that they should not do this, that things are far more complex, et al. You are no doubt correct, but those bad people don't care. They need and want a simple measurement. And they outnumber you.

[Mike Sulzer]

When I go back and reread the post in question, the only question I see is a rhetorical one: why is the measured inductance value different at 1KHz from 120 Hz? I explained this with eddy currents, the explanation you found some time ago. What's this about being outnumbered by bad people who want to measure at 1 KHz because it is a standard? That sounds like something out of some B movie pychological thriller. Standard or not, it is 120 Hz on the Extech that gives the inductance of the pickup coil with good accuracy. All those bad peole who want a simple measurement need only push the frequency button and use 120 Hz, and then use the 1 KHz measurement as an indicator of the size of the effect of eddy currents.

Extech intended the 120 Hz setting for large electrolytic capacitors, but an unintended consequence of including that frequency is to provide a simple, accurate way of measuring the inductance of a pickup coil. Way back four or five yers ago when I first read your posts about eddy currents, I suggested avoiding those effects when measuring coil inductance by using the lowest frequency possible in the measurement. You objected rather strongly, apparently thinking I meant something like 1 Hz. No, 120 Hz is good.

The inductance is a frequency independent quantity, and so it makes sense to measure it at a frequency at which other components in the pickup model circuit to not have a significaant effect (except for the series resistance, which the Extech can handle simultaneously). Parallel loss is important at 1 KHz for pickup coils that use a significant amount of conducting material. When energy storage is the issue, defining a frequency dependent effective inductance can make sense. With pickups, it is the frequency response that is important, and so for that we need a good model of the circuit. A key component is the coil inductance.

You asked why people measure audio components at 1 KHz, and I answered. You replied that they should not do this, that things are far more complex, et al. You are no doubt correct, but those bad people don't care. They need and want a simple measurement. And they outnumber you.

[SkinnyWire]

Measurements for Comparison

I just finished measurements for a 14.4k pickup from a large builder that was supposedly stock in a high dollar custom shop guitar. Here are the results, posted for those interested and maybe to foster further discussion:

Equipment:
Raytek MiniTemp MT6 IR Thermometer
ER Mu115 DVM
Extech 380193 LCR Meter
Syscomp CGR-101 Oscilloscope/Network Analyzer

Measurements:
Ambient Temperature = 75.5°F
DC Resistance = 14.46 kΩ

Inductance and AC Resistance from LCR Meter:
L Series 120 Hz = 8.62 H
RAC Series 120 Hz = 14.66 kΩ
L Series 1 kHz = 8.37 H
RAC Series 1 kHz = 23.66 kΩ
L Parallel 120 Hz = 50.32 H
RAC Parallel 120 Hz = 17.59 kΩ
L Parallel 1 kHz = 10.06 H
RAC Parallel 1 kHz = 141.0 kΩ

Syscomp CGR-101 Oscilloscope/Network Analyzer:
Resonant Frequency via Driver Coil and Lissajous Figure

f0 = 4.17 kHz

Circuit Components for Inductance Calculation
Added Capacitance = 1003 pF
Series Resistor = 98.3 kΩ
Resonant Frequency

f0 = 1.56 kHz

Calculated Inductance

L= 1/C (1/(2πf_0 ))^2= 1/(1.003 x 〖10〗^(-9) ) (1/2π1560)^2

= 10.38 H

Stray Capacitance

C= 1/L (1/(2πf_0 ))^2= 1/10.38 (1/2π4170)^2

= 140 pF

I believe the stray capacitance calculation is reasonable, considering the capacitance per foot of the hookup cable. The calculated inductance is pretty close to the Extech in Parallel/1kHz mode.

[Joe Gwinn]

Measuring audio components at 1 KHz has been the de facto standard since the 1930s.

[Rosewood]

Can someone explain D and Q on the extech as far as pickups go? Maybe on the 3rd grade or monkey level.

[Achiles]

R from L/C/R and R from Q/D/R , what is the diference?

[Joe Gwinn]

D and Q are the inverse of one another: D=1/Q.

[Joe Gwinn]

There is one underlying measurement, that of in-phase and quadrature impedance.

If one measures a resistor, the impedance is all in-phase. The quadrature impedance in infinite or nearly so.

If one measures an ideal capacitor or inductor, the impedance is all quadrature, the difference being if the resulting current leads or lags the driving voltage. The in-phase impedance is infinite or nearly so.

If one measures a practical component, such as a pickup, there is a mixture of resistance and inductance, and there will be significant in-phase and quadrature impedance components.

We usually express this as an inductance and a series AC resistance. But one may express the same thing as a inductance with a Q or D. Nothing real has changed; it's an alternative way to express the same thing.

[Stratz]

Extech 380193 question

Hi all, I bought an Extech 380193 in early 2010 and recently the LCD display starting acting up so I sent it out for repair.
When I got it back I noticed that it now has an anti glare type matte finish on the screen which it did not have before.
It's very annoying and makes the screen difficult to read.

Does anybody else have a Extech 380193 with this type of finish on the LCD screen?

Thanks
Rob

[dai h.]

is it a finish or perhaps transparent vinyl (which you can remove)?

[Stratz]

is it a finish or perhaps transparent vinyl (which you can remove)?

Well, I tried to pick at a corner to see if it was a protective covering but it doesn't appear to be removable.

I'll see if I can post a picture later today.

Anybody else with a 380193 model care to comment?
Thanks.
Rob

[Mike Sulzer]

Well, I tried to pick at a corner to see if it was a protective covering but it doesn't appear to be removable.

I'll see if I can post a picture later today.

Anybody else with a 380193 model care to comment?
Thanks.
Rob

Yes. This is the worst display I have ever seen on any professionally designed instrument. To begin with, the secondary information is too small, requiring extreme focal correction for old eyes. With that stupid blurry stuff over it, I have to get within a few inches in order to read it, even in bright light. Or I can remove all correction and use my natural extreme near sightedness. This is a fairly new instrument, and I nearly sent it back. Determining the mode of operation or the frequency is just way too difficult.

I tried lifting a corner, but stopped for fear of making it worse. I am tempted to just remove the plastic all together.

[Joe Gwinn]

Well, I tried to pick at a corner to see if it was a protective covering but it doesn't appear to be removable.

I'll see if I can post a picture later today.

Anybody else with a 380193 model care to comment?

Haven't had the problem as the LCD hasn't failed.

I would call Extech up and ask before starting to fiddle. They're in the Boston area.

[SonnyW]

Yes. This is the worst display I have ever seen on any professionally designed instrument. To begin with, the secondary information is too small, requiring extreme focal correction for old eyes. With that stupid blurry stuff over it, I have to get within a few inches in order to read it, even in bright light. Or I can remove all correction and use my natural extreme near sightedness. This is a fairly new instrument, and I nearly sent it back. Determining the mode of operation or the frequency is just way too difficult.

I tried lifting a corner, but stopped for fear of making it worse. I am tempted to just remove the plastic all together.

Mine is old and the display is fine, but just as a thought, has anyone considered trying the software that comes with most of these? Mine came with a CD and a cable. I have an old laptop that I keep at my bench, and usually an external display there as well and I seldom have to look at the display on the Extech. It is replicated on the PC display. It was pretty straightforward to set up. I did it to automatically record my test data into an excel spreadsheet, but I leave it running and use the PC display even when I am not recording data.

[ScottA]

The display on mine is OK, too.

I got mine used off of ebay (really cheap, too!).

Sonny, is there any way I could get that software? I would really like to automate my measurement collection. I measure every pickup for final QC and the hand translation gets old after awhile, as well as providing plenty of opportunities for error.

Thanks,

Scott

Mine is old and the display is fine, but just as a thought, has anyone considered trying the software that comes with most of these? Mine came with a CD and a cable. I have an old laptop that I keep at my bench, and usually an external display there as well and I seldom have to look at the display on the Extech. It is replicated on the PC display. It was pretty straightforward to set up. I did it to automatically record my test data into an excel spreadsheet, but I leave it running and use the PC display even when I am not recording data.

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