# resistors change value with tension?

Is it just me or do carbon and metal film resistors change their value by almost 10% with the applied pressure?

winner10920: Is it just me or do carbon and metal film resistors change their value by almost 10% with the applied pressure?

If you mean voltage for your term 'pressure', then no, a resistor's ohms value is independent and not directly effected by the value of the applied voltage.

However most resistors do have a temperature coefficient factor where it's resistance can vary depending on it's operating temperature, which in turn is determined by it's power dissipation value, which is the product of the voltage applied and current flowing through the resistor. A 10% change in resistance value might be possible if the resultant power dissipation Vs temperature coefficient is factored in. You would have to consult the resistor's datasheet for the information needed to calculate worst case resistance variation Vs operating temperature.

Lefty

Mecahincally stressed carbon resistors can change in resistance.

As a kid I had a slotcar set that compressed a carbon stack to vary the resistance to control the speed of the cars.

Im talking about putting my multimeter on a resistor 10k 1% tolerance metal fil resistor and being able to change the resistance like 300 ohms by just pulling the leads as I measure it

winner10920: Im talking about putting my multimeter on a resistor 10k 1% tolerance metal fil resistor and being able to change the resistance like 300 ohms by just pulling the leads as I measure it

Well that's more like 3% and maybe it's just a result of the construction of the resistor or making better stronger contact with your ohm meter leads, who knows, but that resistor is not made for that property.

That's why I thought it was weird, the tension dropped the resistance Its probably not that im not getting good contact or it would raise in ohms not lower the carbon and the metal fil did the exact same thing can u try it and see what happens? I wonder if its cause I buy my resistors cheap on ebay...

winner10920:
… and being able to change the resistance like 300 ohms by just pulling the leads as I measure it

This is not likely to be from mechanical stress, but rather your body resistance acting in parallel with the resistor (and meter). This will result in a lower reading and the effect will increase with a firm grip (such as is required when you pull the leads). For anything except low ohm resistor’s, it is better not to touch the leads (or meter probe pins) when you need an accurate reading.

You might have mechanically damaged the resistor so the endcaps are loose - they are not rated for any tension at all.

If the resistance goes down, I'm going to say Ben is right... It's the resistance of you body in parallel.

If the resistance goes up, you might be right... and I'd be surprised, especially if the experiment is repeatable with different resistors.

You can use a 200 MOh multimeter to see microphonic effects.

I can sell one for \$20, including digital capacity tester, and battery

MarkT: You might have mechanically damaged the resistor so the endcaps are loose - they are not rated for any tension at all.

or the solder barrier is bad inside the resistor, maybe from sulphur vapor. could be cheaply made resistors. what color is the case?

I tried it wit carbon resistors from radioshack and metal fil resistors from ebay, same outcome, I doubt its my body as I don't put more pressure on the leads, just the resistor, I even tied it to the leads and got the same results, and it works both ways, for the 10k I was at 9.56 with no pressure at all, I push it together and I get 9.65, pull apart and I get 9.40 that's a decent change, (and annoying how the 1%tolerance resistor is 4% off) Anyone ekse try it yet?

winner10920:
Anyone ekse try it yet?

I just tried it:

• 10 kOhm resistors, 5% carbon and 1% metal-film
• DMM readout resolution of 0.001 kOhm
• Electrical connection via croc-clips
• Force applied via pair of insulated pliers gripping leads near resistor body
• Tension & compression along axis of resistor, approx. 20N (2kg)

No measurable effect (<0.01%)

I guess its just the cheap shit i buy then, lol some nice cheap tension resistors

Maybe they are based on charcoal particles not a real carbon film :)

Having such resistors is uncommon, there would be too much microphonic effects

What exactly does microphonic mean in this sense?

not exactly, it means undesired effects on circuit elements. there's a wiki article too.