How to create resistance with negative TC?

[aronake]

Hi,

Creating positive TC to compensate resistors with negative TC is easy. Just use some copper wire.

But how can negative TC be created at 23 degree C?

There is of course some resistors that have negative TC that can be used to compensate other positive TC resistors, but what to do if wanting a more direct impact?

[Electro Fan]

Lower the ambient temperature (if possible, turn on air conditioning to cool the test area).

[Mickle T.]

The traditional way to regulate the temperature coefficient in the production of metal-foil and microwire resistors is to select appropriate modes of precision vacuum heat treatment of the alloy. (But I’m just not sure about top-end resistors, such as Vishay Z-foil, Russian NV-technology, etc.)

[dietert1]

Lower the ambient temperature (if possible, turn on air conditioning to cool the test area).

Yes, often the TC depends on temperature. So you may need to find the zero TC temperature.
Not all precision resistors have that nice TC curve with slope dTC(T)/dT small enough for the nonlinear contribution to exhibit its maximum or minimum within a practical temperature range. Then you need a combination with some NTC resistor. Using a NTC plus a third resistor to adjust the "gain" you can always get to zero.
What you need to start with is a setup for measuring TC as a function of temperature.

Regards, Dieter

[aronake]

Lower the ambient temperature (if possible, turn on air conditioning to cool the test area).
t

Yes, often the TC depends on temperature. So you may need to find the zero TC temperature.
Not all precision resistors have that nice TC curve with slope dTC(T)/dT small enough for the nonlinear contribution to exhibit its maximum or minimum within a practical temperature range. Then you need a combination with some NTC resistor. Using a NTC plus a third resistor to adjust the "gain" you can always get to zero.
What you need to start with is a setup for measuring TC as a function of temperature.

Regards, Dieter

This was good input! Based on this suggestion i did some googling on how a NTC thermistor is made and found on littlefuses webage:

"NTC thermistor manufacturing begins with the precise blending of raw materials into an organic binder solution. These raw materials are powdered transition metal oxides such as manganese, nickel, cobalt, and copper oxides. Other stabilizing agents are added to the mix as well. The oxides and binders are combined using a wet process technique called ball milling. During the ball milling process, the materials are blended and the particle size of the oxide powders are reduced. The completed homogeneous mixture has the consistency of a thick slurry. The exact composition of the various metal oxides and stabilizing agents determines the resistance-temperature characteristics and resistivity of the fired ceramic component."

https://www.littelfuse.com/technical-resources/technical-centers/temperature-sensors/thermistor-info/thermistor-manufacturing.aspx

So pretty complicated and no where i have seen have they been very specific on what is mixed togoether. Cupper for postive TC is million times more straight forward.

I would be interesting to know more how vishay get is pretty linear TC on VHP101 and similar resistors.

[MiDi]

A good read how to compensate TCR is on xDevs.