Varying resistance readings depending on how I connect my meter

[Martyn Arthur]

TL;DR

different readings from links in breadboard to direct meter connections

i have 1.6 ohm 2w resisors 3 samples all of which test 1.6 ohms when linked to meter. when tested through a breadboard they read 2 ohms; an explanation would so much be appreciated please?
Thanks
Martyn

 

[Dale]

The breadboard seems to add 0.4 ohms of resistance.

 

[Martyn Arthur]

Thnks;but when I link the 3 they read 3.7 ohms?
Martyn

 

[Martyn Arthur]

Its a bare circuit and has been tested at different points.
Martyn

 

[Dale]

Well, either your multimeter is not good and is not reading the actual resistances, or your breadboard is adding some resistance. I don't know what else to tell you. There really isn't another possibility.

If you have another multimeter then try the same measurements with a different device. Otherwise, try the same measurement multiple times with the same multimeter (completely take down and reassemble the circuit and all of the multimeter connections at least twice).

If you are confident that the multimeter works, then the breadboard is adding resistance. Your errors are small enough that it really could be either.

 

[Baluncore]

when tested through a breadboard they read 2 ohms;

There is more contact resistance somewhere.
Depending on the breadboard construction, the contacts may be thin phosphor bronze shim, tin plated, and with little contact area.

How about a picture of the setup used to make the measurements.

 

[Martyn Arthur]

Thanks I tried every option i could think of before reaching out to you; changed the resistors changed the breadboard and changed the monitor???? just don't know what else to try.
Martyn

 

[Dale]

If the multimeter is accurate then it is accurately telling you that the breadboard is adding resistance. There really isn't anything to "try", that is just physics. Breadboards add resistance (and capacitance).

 

[Martyn Arthur]

Ok I can live with that; thanks or your help; I will try it with a clean pcb.
Thanks
Martyn

 

[berkeman]

I will try it with a clean pcb.

Wait, is this a soldered PCB connection, or a spring-loaded breadboard connection? As already mentioned, some pictures would help. Also, if these are power resistors, the leads may be too large for a simple plug-in breadboard...

https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard/why-use-breadboards

 

[berkeman]

Thnks;but when I link the 3 they read 3.7 ohms?

3 x 1.6 = 3.7 ??

 

[Martyn Arthur]

just pcb board connections of 3 series resistors and probes inserted adjacently
Martyn

 

[DaveE]

I think you're just learning why I hardly ever used those things for my breadboards. Plus, they aren't stable or durable. Basically, I hate those things for wasting my time. It doesn't take long to solder after you place components.

Anyway, I'm not sure what to add, except that dealing with instrumentation issues is part of an EE's life. They all have issues at some point. It's your job to understand your measurements/instruments, not just to collect data blindly.

 

[Martyn Arthur]

Seriously its a whole section of a course in one. Thank you; this closes it for me!
Martyn

 

[sophiecentaur]

There really isn't another possibility.

Actually there are many possibilities. Positively the last system for accurate measurements of very high or low resistances / voltages or high frequencies / currents would be with a breadboard with clips. Breadboards are a quick and dirty method for testing viability of a basic idea. That would involve resistances of at least 10 Ohms and less than 10M, safe voltages and just a couple of Amps - you know what I mean. Breadboards are NOT simulations.
I can't find an actual schematic diagram of the set up so do we know how the meters have ben connected? How low resistance is the ammeter and does the PD measurement happen to include the drop across the ammeter. Even using the same meter to measure both quantities can affect what you get.

I'm staggered that so many people won't or can't solder joints.

 

[Martyn Arthur]

Thanks for the response; soldered the resistors and readiinng was perfect; comments about breadboards noted with gratitude.
Martyn

 

[sophiecentaur]

Glad to be of help.
I learned those lessons many years ago (many). If you google resistance measuring techniques, look for a site with circuit diagrams and 'convincing' use of maths and terms. Treat Electrics the same as (your own) money. Intuition and stuff you can often hear can encourage sloppiness and inhibit success.

You can pretty much trust PF not to mis-lead you. Good luck.

 

[Martyn Arthur]

Away to go then
Thanks again