Basic Knowledge

Basic Knowledge of Trimmer Potentiometers

SubTitleIcon6    What is Trimmer Potentiomerets

Trimmer Potentiometers are semifixed potentiometers that it's resistance can be changed freely. They are used in some applications that usually almost have no need to adjust again after first time adjustment. So to avoid be touched easily, they are set inside of products. On the other hand, rotary position sensors are also called variable resistor, but they are the parts that adjusted by turning the knob outside of products.


There is a table about the classification of trimmer potentiometers.
In general classification, there are sealed type products with high regard for environment resistance and open type with high regard for cost. And there is also another way for distinguishing, multi-turn products with high resolution and single - turn products with high cost performance.

Structure/
Adjudtment turns
Sealed type Open type
Single - turn Sealed type/Single - turn Open type/Single - turn
Multi - turn
( ) number of rotation
Sealed type/Multi - turn  

SubTitleIcon6    Principle of Trimmer Potentiomerets


A fixed resistor with a mechanism to change resistance construct a trimmer potentiometers. The principle is with the changing of resistive element length according a wiper sliding, the resistance will be changed. Use this method, with same sectional area, the resistance can be changed relative to resistive element length, and products can be manufactured in low cost.

R = ρ × L/S
R: Resistance [Ω]
ρ: Resistivity [Ω/m]
L: Resistive element length [m]
S: Resistive element sectional area [m2]
Principle of Trimmer Potentiomerets

  • The position of contact point decide the length of resistive element.
    Resistance between No.1 and No.2 (R12) will become higher if contact point become closer to No.3.
  • For easy introduction, we drew the resistive element like a rectangular solid. Actually, almost resistive element is round shape (U - shaped) .

    So the track of wiper is circle, and resistance is decide by the angle of wiper.


SubTitleIcon6    Change in resistance of Trimmer Potentiometers

There is the relationship between wiper position (angle) and resistance in below figure.

*The output wave is besed on below conditions.
Resistive element is round shape (U - shaped) /Single - turn/No whirl - stop.

Construction
Single - turn, no whirl - stop type
Fig1. Construction Single - turn, no whirl - stop type

The relationship between wiper position (angle) and resistance
Fig2. The relationship between wiper position (angle) and resistance



SubTitleIcon6    Feature of Trimmer Potentiometers

By using trimmer potentiometers, it is no problem to set surrounding circuit constant roughly.

Would you please use trimmer potentiometers if it is difficult to decided on a resistance value in your circuit. You can design your circuit roughly and quickly as the result.

In case of fixed resister, you will need much time to decided on the value.In case of trimmer potentiometer, you can desing your circuit easily and speedy.