Impedance Measurement

"Pete M"

....... Phil

The tip and sleeve need cleaned. They expand from the heat and don't make good contact. A soft brass brush and a tiny spot of "Anti seize" compound will correct the problem, but if you need a grounded tip for ESD sensitive work, the iron needs to be cleaned daily. (Or every few hours of use). Our limit was 3 ohms from the tip to the metal box the iron was plugged into, whenever any soldering iron was hot.

Hi, Pete. You might be seeing the effects of leakage current on your ohmmeter when the power is on. You should try measuring with power off.

Using a cheapie DMM to measure low ohms can be kind of chancy. If the measurement is critical, and you don't have a Kelvin (4-terminal) ohmmeter, use a 10V supply with a series 10 ohm, 10 watt resistor as a voltage/current source, and then measure the actual voltage you get from tip to GND when you apply current. You can then infer resistance using Ohms law. That will be accurate to within the tolerance of the resistor.

Good luck Chris

If there is enough leakage current to affect the reading, the iron is defective.

try it with an moving-coil meter.

Bye. Jasen

Why would that make any valid difference? In fact, it would make it harder to get a valid reading.

I used a Data Precision digital meter on my bench for four years. If any of the hot soldering irons hadn't been used in 15 minutes or more, the hot tip was touched to a scrap of copper clad PC board, with a drop of solder. If they read under three ohms, I used it. if not, I cleaned it and retested. I also tested and calibrated every soldering iron in the company a couple times, after one of the MEs died of a Brain Aneurysm.