DCR ,Turns

[J M Fahey]

I thought this thread was already dead and buried, but because it keeps resurfacing:

1) measure your DCR with a standard universally trusted multimeter such as a Fluke model xxx (insert proper number here).
It will measure DCR by passing a known and calibrated value of DC current through it, measuring DC voltage drop across a series resistor of known value, then displaying such DC voltage in a display but calibrated in Resistance values, scale unit: Ohm.
I know you know this, I´m trying to get through to a particularly obnoxious customer.

2) just in case recheck with a couple other multimeters, value should be within 5% or less.

3) then ship pickup.
If customer complains, tell him to get a Flke *** (same model as yours and should be a very popular one, so either he has or can borrow one)

If his value is within 5% (it should, or one of the Flukes is dead/broken/whatever) then smile and tell him "hope you enjoy it, bye bye"

If he says the <$100 Flukes agree with you but the $2000 meter does not, ask him: "is it a multimeter or a bridge or what the heck?" If he answers "bridge" tell him: "whatever his displays does not apply, you guarantee DCR , not ACR or R derived from an AC measurement, period"

[David Schwab]

Plus people make the mistake of holding the meter probes on the pickup wires by pinching them in their fingers! Now the resistance of their body is in parallel. I get a reading of ~ 5 MEGOHM touching both probes. It will give a slightly lower reading on the pickup. I always use the little spring clip probes.

[copperheadroads]

Plus people make the mistake of holding the meter probes on the pickup wires by pinching them in their fingers! Now the resistance of their body is in parallel. I get a reading of ~ 5 MEGOHM touching both probes. It will give a slightly lower reading on the pickup. I always use the little spring clip probes.

True , I do have one cheaper more basic meter that you hands has no effect on resistance ,unlike most of my meters .
Very strange is could be a low battery causing the glitch

[12xu]

.6k is a pretty big gap for meter calibration issues.

Your dcr for your turns count is about right.

Seams strange that you have more than one guy with a big difference in readings.

I have a $50 dollar Triplett and a $600 fluke, they both give me the same readings.

[ReWind]

Here's one that wasn't mentioned - Your "DCR : turn count" ratio will vary with winding speed, too. If you are spinning the bobbin really fast, the coil will be more of a donut shape and pull more wire off the spool per turn as it bulges out. Different brand bobbins and your particular technique for attaching the coil start to the hookup lead will also give different results, as the internal size/shape of the coil can vary.

Of course, that doesn't account for your pickup reading different on different meters so I think the ideas others have already mentioned are a likely cause.

Are you metering them right after they are built? DCR will drop a bit as the coils settle and will also read higher when you have recently soldered the hookup leads or cover, heating up parts of the pickup.


Aside from the actual cause of discrepancy, if your customers are returning pickups because the DCR is a little off, you need to educate your customers about what matters and what doesn't.

[kmensik]

Plus people make the mistake of holding the meter probes on the pickup wires by pinching them in their fingers! Now the resistance of their body is in parallel. I get a reading of ~ 5 MEGOHM touching both probes. It will give a slightly lower reading on the pickup. I always use the little spring clip probes.

Yes, I always try to avoid that, because between my hands I can measure even 700kOhm when holding the probes firmly, with dry hands. One of my friends is so conductive it goes to tens of kOhm.