How Are "Henries" Measured?

[Als Kimp Tones]

Hello, I'm new. It seems that henries are an important spec for pups. What does it take to measure? Thanks

[Rob S]

I use the inductance setting on my multimeter but as an aside, I got nearly 1.25 million hits when I googled 'Inductance Measurement' as compared to over 35 million for "Troll".

Rob.

[Magnetosaure]

Hi,

First post for me too...

I think that most of the pickups manufacturers indicate the inductance of their pickups measured with a test frequencie of 1 KHz. The measurement change if you use a different frequencie.

I'm I right?

[soundmasterg]

What you want to do is to get the Extech meter that just about everyone uses. It is model 380493 I think. I'm not at home right now so I can't look at it and say thats it for sure or not. Maybe someone else who has one can confirm if I have the number right or not. They're under $200, and can measure inductance, Q, and AC resistance at 1 Khz and 120 Hz in series or in parallel. Most people seem to use the 1 Khz setting. They're quite accurate and easy to use, and will give you some real useful info about the pickups. You can use high AC resistance numbers in relation to the DC resistance number to tell if you have a shorted coil for instance.

When measuring any of those, the reading does change with frequency, and also with temperature. So if you measure in your garage on a cold day, you will get lower numbers than if you measure on a hot day.

[Ray Ivers]

Apex Jr. has a Victor VC6243 LCR meter for $50! which I found after paying about $170 for my B&K... :(

Ray

[Als Kimp Tones]

Hey, thanks everyone.I think I now know what direction i need to go.Winding pickups isn't rocket science,but it sure is science.

[soundmasterg]

Ray how accurate is that one you got at Apex Jr? And does it test as many things as the Extech? Everyone here seems to use the Extech, and I've found out that companies like Rickenbacker use it too. I like my Extech a lot as its really easy to use, very flexible, and isn't priced too badly.

The hard part is equating the science of pickup making to actual real world things. You can have all the inductance, Q, and AC resistance specs in the world, but if you don't know what those numbers mean in relation to a pickup, then it doesn't do you any good.

[Ray Ivers]

Greg,

I really didn't accuracy-check it at all - in fact, my buddy Scott was over and I gave it to him as a gift; I waited far too long to get my first cap checker (and 22 years for an LCR meter!) and I didn't want him to do the same thing. :)

Equating the science to the sound IMO requires a "bridge" - for many this is experimentation and empirical methods combined with measurements, for me it's all of these things plus math (mainly to compute gain and L/C/LC/RC/etc. filter behavior - I let the computer handle this part, believe me), for others it may be purely theoretical and mathematical using measurements only for confirmation before listening tests begin, I don't know. So far I've only used my LCR meter to check capacitor values and OT primary inductance, but I know I'll use it more as I get used to having it around.

Ray

[Dave Kerr]

Ray how accurate is that one you got at Apex Jr? And does it test as many things as the Extech? Everyone here seems to use the Extech, and I've found out that companies like Rickenbacker use it too. I like my Extech a lot as its really easy to use, very flexible, and isn't priced too badly.

The hard part is equating the science of pickup making to actual real world things. You can have all the inductance, Q, and AC resistance specs in the world, but if you don't know what those numbers mean in relation to a pickup, then it doesn't do you any good.

According to this Yahoo store (http://store.imarketcity.com/vcprdicaandi.html), the specs:
# CAP: 0 - 2n - 20n - 200n - 2u - 20u - 200u - 1000uF
# Inductance: 0 - 2m - 20m - 200m - 2H - 20H
# Capacitance accuracy 23°C +/- 2°C: < 0.5Uf +/- 1.0%, > 0.5uF +/- 2.0%
# Inductance accuracy 23°C +/- 2°C: < 0.5uH +/- 2.0%, > 0.5uH +/- 5.0%
# C Temperature coefficient: < 0.5uF +/- 0.1% /C, > 0.5uF +/- 0.2% /C
# L Temperature coefficient: < 0.5H +/- 0.2% /C, > 0.5H +/- 0.5% /C
# Zero Error: C < 5pF, L > 10uH
# Size: (inches) 3.8 x 8 x 1.6
# Weight: (Lbs) 1.37

[soundmasterg]

Those specs don't say anything about what frequencies it tests at as far as the inductance. It would be helpful to know that if someone was going to use it for pickups, since they are usually pretty high frequency compared to what the meters test at.

Ray, how do you use the LCR meter to check the OT primary inductance? That would be useful for me to know how to do. I'm sure I could use my Extech for that if you've been using that one you had.

Greg

[Ray Ivers]

Greg,

Ray, how do you use the LCR meter to check the OT primary inductance? That would be useful for me to know how to do. I'm sure I could use my Extech for that if you've been using that one you had.

My exact method? OK, well, first I measured a 20H OEI choke - 20.0H, great. Then I connected it across the OT primary with secondaries disconnected - no reading at all (IMO it's important to include this step to fully "learn the lesson", so to speak ;)). Then, it was pointed out to me that that wouldn't work :D so I shorted the secondary, measured it again, and got my reading. In retrospect, I suppose loading the secondary with the proper load resistance would have given the most accurate reading, but the one I got was ballpark correct so I didn't try that (I will from now on, though).

FWIW, so far I really don't like the B&K 875B at all, although I didn't compare it to the one I gave away (I'm thinking I should have given this one away instead :)). It seems very reluctant to give readings, and just kind of finicky in general, a far cry from my Fluke 87 DMM which just plain gives me what I ask for, every time.

Ray

[soundmasterg]

Thanks Ray! I'll have to try my Extech and see if I can get a decent reading on some OT's. I've got a B & K DMM, but I can't recall which model. It works fine for me.

[Rob S]

You may be interested in what R.G. Keen has to say here:

http://www.geofex.com/Article_Folders/xformer_des/xformer.htm

- particularly the terminology part at the top

[David Schwab]

My method is to tell Henry to stand against the wall, make a mark with a pencil and get my tape measure... :p

OK... ok... it's Friday... everyone have a great weekend! :D

[Rob S]

My method is to tell Henry to stand against the wall, make a mark with a pencil and get my tape measure... :p

OK... ok... it's Friday... everyone have a great weekend! :D


I think it's saturday and I feel just like you did there;)

[Mystic]

Isn't Henry the guy that messed up Gibson?
It's Saturday and I had to work.....:(

[Possum]

the cheap multimeters aren't good for inductance readings at all. They have autoswitching from 120-1Khz. My Meterman 37xr does this and it fails miserably at reading guitar pickups in the 1khz range, it will hit around 4 henries then read OT and switch to 120H, totally useless for guitar pickups. I had the damn thing for a year and when I got the Extech found out most of my readings weren't very accurate at all. The Extech is pretty much the ONLY small LCR meter that works for guitar pickups. Multimeters with inductance add ons don't work right. Bill Lawrence is another guy who uses the Extech you can see it pictured in his ad in VG. LCR readings are useful but unless you buy a super expensive HP LCR meter that reads also at 10khz, you really don't get the full picture of whats going on in the coil. Useful it is though...

[David Schwab]

Isn't Henry the guy that messed up Gibson?

Yeah, and he also messed up Opcode, and Oberheim, and Steinberger, and Tobias, and....

[Sweetfinger]

The booklet says it measures up to 2H using 150uA current @ 1Khz, 20 Henries using 15uA @ 100 Hz.

I measured some common household items:

red reissue Fasel inductor--------- 638 mH
dunlop black inductor------------- 585 mH
old organ inductor stamped 500mh-508 mH
'75 Jazz Bass pickup, 7.5K---------- 6.2 H
recent mex strat pup w/steel poles-- 7.0 H
Duncan screamin demon trembucker- 9.2 H
some kinda Tele rhythm, alnico------ 5.4 H
10" alnico 8 ohm speaker------------ 0.7 mH and beeped
Valco 2X 6L6 OP Xformer, open secondary was 10.4 H and with secondary connected to 8 Ohm load, measured 3.95 H.

Do these readings seem correct? The wah inductors seemed right on.

[soundmasterg]

You'll notice it says it measures only up to 2H @ 1000 Hz. That isn't high enough as even your lowly Strat pickups are about 2.2 henries. Every one of those pickups measured is off from where it should be and is much too high. Even a run of the mill P90 is going to be about 4.5 henries, and based on what you posted so far I bet your meter would say it was more like 10 henries. Take a look at the Extech 380193 specs at this site.


http://www.tequipment.net/Extech380193.asp

[Joe Gwinn]

The booklet says it measures up to 2H using 150uA current @ 1Khz, 20 Henries using 15uA @ 100 Hz.

I measured some common household items:

red reissue Fasel inductor--------- 638 mH
dunlop black inductor------------- 585 mH
old organ inductor stamped 500mh-508 mH
'75 Jazz Bass pickup, 7.5K---------- 6.2 H
recent mex strat pup w/steel poles-- 7.0 H
Duncan screamin demon trembucker- 9.2 H
some kinda Tele rhythm, alnico------ 5.4 H
10" alnico 8 ohm speaker------------ 0.7 mH and beeped
Valco 2X 6L6 OP Xformer, open secondary was 10.4 H and with secondary connected to 8 Ohm load, measured 3.95 H.

Do these readings seem correct? The wah inductors seemed right on.

The inductor values are probably correct, but I would be very suspicious of the pickup values.

Aside from the test frequency switching from 1 KHz to 120 Hz right in the middle of the inductance range of real pickups, there is a deeper problem: Most handheld LCR meters are designed to measure fairly "pure" inductances only, but pickups are not at all pure, having a fairly high resistance for their inductance, causing many LCR meters to be wildly off.

A good test is to take one of the relatively pure inductances (such as the inductors listed above) and wire a pot in series, and measure the inductance of the combination. Does the indicated "inductance" vary by much as the resistance is increased? If yes, measuring pickups with that LCR meter simply won't work.

If one is energetic, one can also build a Maxwell-Wein Impedance Bridge (http://home.comcast.net/~joegwinn/), which is what was used to validate the Extech measurements. This is the acid test, and can be used for any frequency, not being limited to 1 KHz and 120 Hz.

So far, the only ~$200 handheld LCR meter that is proven to work with guitar pickups is the Extech 380193, which is fast becoming the industry standard. The standard test frequency for pickups is 1 KHz; the 120 Hz is for power-supply components.

[Sweetfinger]

I will probably use the Victor more for ID of wah inductors and power supply chokes, anyway.

The link for the Joe Gwinn bridge is not working for me. Fresh link anyone?

[Joe Gwinn]

The link for the Joe Gwinn bridge is not working for me. Fresh link anyone?

The URL is correct, but the trailing slash parens confused it. It turns out it needs the url tag and antitag.

Try http://home.comcast.net/~joegwinn/.