Extech automated data collection

[salvarsan]

The Extech 380193 LCR meter has an optical+serial data cable so you might (in principle) collect the measurements on your workstation.

There are practical issues that show the 380193's 10+ year age.

1) It handles serial data requests only once per second, although the display updates 3 times/second.

2) Setting up the meter by serial line reliably takes 5 seconds.

3) If you send it a command too soon after setup, the Extech either stalls or is slow to stabilize.

4) You can request and get data before the meter has stabilized and must request 3 or 4 readings to identify outliers.

Comprehensively collecting R,L, and C at 120Hz and 1kHz is a 20-30 second chore, ---
3X as long as doing it by hand (assuming you don't log data).

An inductance data string for one of Steve Kersting's vanilla P90's looks like:
LRASA0854341605422996433363__________
and means
Serial Inductance = 8.543 H @1kHz
AC resistance = 16.05 kOhms,
Q factor = 3.336

To be fair, you could adequately characterize a pickup using only L and C measurements on the primary display with Resistance on the secondary.

I'm hoping Extech's newer version, the LC200, does a better job with the serial IO.

[salvarsan]

Correction: As Joe Gwinn noted, an LCR capacitance measurement on a guitar pickup is nonsense because the test frequency is not at resonance.
A meaningful characterization is DC Resistance, followed by inductance and AC resistance at 120 Hz and 1kHz.

I just pulled the trigger on the newer LCR200 and also expect its comm protocol document.
News at 11.

[salvarsan]

Extech LCR-200 serial protocol document

Extech graciously and quickly sent a protocol document for the LCR200 L/C/R meter.


Its data rate is 8x as fast as the 380193 that we know and love, and the data format is more compact.
That's 9600 baud, 8,N,1, 17 byte packets versus 1200 baud,7,E,1, 39 byte packets

It can also test at 10kHz and 100kHz although those measurements may be irrelevant for guitar pickups.

The laconic 57kB LCR200 RS-232 protocol document is appended below.

LCR-9184-RS232.pdf

[Mike Sulzer]

Correction:
A meaningful characterization is DC Resistance, followed by inductance and AC resistance at 120 Hz and 1kHz.

But you have to do the dc resistance separately or hope that the 120 Hz measurement is close enough (which I expect it is in most cases for pickups). When you measure in the R position, the measurement is still made at one of the two frequencies. I accidentally verified this by measuring a woofer in a cabinet. You can hear it, and the measurement at either frequency is not the same as a true dc measurement made with a DVM.

Why do they have the "R" position? Beats me, maybe Joe knows.

[salvarsan]

But you have to do the dc resistance separately or hope that the 120 Hz measurement is close enough (which I expect it is in most cases for pickups). When you measure in the R position, the measurement is still made at one of the two frequencies. I accidentally verified this by measuring a woofer in a cabinet. You can hear it, and the measurement at either frequency is not the same as a true dc measurement made with a DVM.

Why do they have the "R" position? Beats me, maybe Joe knows.

I think the Extech gives you a resistance at a frequency, i.e, Rac.

A pickup at hand measures:

Rdc = 9.155 k, Temp = 77.9F,
Rac(120 Hz) = 9.303k
Rac(1kHz) = 15.64k

L(120Hz) = 8.933 H
L(1kHz) = 8.547 H

In round numbers, 150 ohms difference is about 90 feet of #42AWG, nearly 200 winds on a Strat pickup. They aren't close enough to fall within copper temperature coefficient effects, so yes, Rdc needs to be a separate measurement.

Joe Gwinn could probably tell us more about eddy current contributions from the data set.

[Mike Sulzer]

A pickup at hand measures:

Rdc = 9.155 k, Temp = 77.9F,
Rac(120 Hz) = 9.303k

So Rdc and Rac(120 Hz) are about 1.6% different. Are you confident that the two meters are mutually calibrated closely enough so that you believe it?

[David King]

I searched on line but couldn't find a price for the LCR200 yet. Is it a lot more than the old 380193?

[tedmich]

I searched on line but couldn't find a price for the LCR200 yet. Is it a lot more than the old 380193?

is this it?

https://www.google.com/search?q=exte...w=1333&bih=625
about $260

[salvarsan]

So Rdc and Rac(120 Hz) are about 1.6% different. Are you confident that the two meters are mutually calibrated closely enough so that you believe it?

Quit being a nudge.

Yeah, they're good to 4 sig fig on the same resistor.
It's the essential difference between the 20,000 count LCR and a 50,000 count DMM.

[salvarsan]

I searched on line but couldn't find a price for the LCR200 yet. Is it a lot more than the old 380193?

It's enough more. $260 MSRP, lowest street price is $235.

Try Google Shopping for pricing, or find a vendor on the Extech site.

According to Extech the LCR200, while more capable (more test frequencies, improved accuracy, both AC and DC resistance), it's a "read-only" device -- you can't configure it over the serial line.

If you already own a 380193, the LCR200 is a minor improvement.

If you don't own an LCR meter, the LCR200 is the better choice.

[Joe Gwinn]

Why do they have the "R" position? Beats me, maybe Joe knows.

Because they can. There are six ways to present the one measurement the meter makes, of complex impedance. Extech has no way to know what we care about, so they provide all six answers.

[Joe Gwinn]

I think the Extech gives you a resistance at a frequency, i.e, Rac.

Exactly.

A pickup at hand measures:

Rdc = 9.155 k, Temp = 77.9F,
Rac(120 Hz) = 9.303k
Rac(1kHz) = 15.64k
...

Joe Gwinn could probably tell us more about eddy current contributions from the data set.

The eddy current load is proportional to Rac minus Rdc.

[David King]

Thanks, though I don't see anyone actually selling it for less than 260 so it may be a wait and see for me. It would certainly be fun to have.

[salvarsan]

Thanks, though I don't see anyone actually selling it for less than 260 so it may be a wait and see for me. It would certainly be fun to have.

My discussion with a local vendor:
"The best online price is $234. I want to buy locally. Can you match or beat $245 so the 6% tax doesn't bite too hard?"
They said: " $234. No tax."
I said: "Cash."
They said, "It's Monday. Pick it up Thursday."

[David King]

Hmmm, I wonder what a group buy would do for the price? If the local place is paying "B Mark" (40% off "retail") then they have some room.