# General Concepts

#### Potentiometer configuration

The pin that corresponds to the reading of the wiper is pin B.
A and C are connected to the ends of the resistor, being pin A the initial position and C the final position.

#### Electric use

##### Variable resistor

When pins A and B or C and B are connected, the current goes through the wiper (blue line).
Depending on where in the resistor the wiper is placed, it indicates
a lower resistive value than the whole resistor would (we say it is used as variable resistor or rheostat).
The output is measured in ohms.

##### Voltage divider

When a voltage is applied between the ends of the resistor (A and C), the current goes through the resistor, not the wiper.
The wiper sees a proportional share of the voltage applied between the ends (we say this is a Voltage Divider).
The output is a voltage, measured in V.

#### Resistance

Total resistance (RT):
It is the resistance found between the input terminal and the wiper when the latter is positioned to give the maximum value.

Electric noise or contact resistance (RC):
Noise is any variation in the output signal that does not correspond to a similar variation in the input signal. It appears in the contact point between the resistive element and the wiper. It is measured in Ohms.
This noise can also be measured as “contact resistance variation” (CRV), which is expressed in the percentage of change between the initial resistance and the value of the resistance after a test. It is measured statically and dynamically.  ACP’s potentiometers have less than 5% CRV.

#### ACP’s standard resistive values

The standard values are as follows, although values out of range can also be studied.

100Ω 200Ω 220Ω 250Ω 470Ω 500Ω 1KΩ 2KΩ 2.2KΩ 2.5KΩ 4.7KΩ 5KΩ 10KΩ 20KΩ 22KΩ
100 200 220 250 470 500 1K 2K 2K2 2K5 4K7 5K 10K 20K 22K
25KΩ 47KΩ 50KΩ 100KΩ 200KΩ 220KΩ 250KΩ 470KΩ 500KΩ 1MΩ 2MΩ 2.5MΩ 4.7MΩ 5MΩ
25K 47K 50K 100K 200K 220K 250K 470K 500K 1M 2M 2M5 4M7 5M

#### Variation laws - Tapers -

The standard taper is linear (A). Log (B) and Antilog (C) tapers are also available, as well as special tapers according to customer’s specifications. For example, a special taper can be matched with a potentiometer with detents (click effect), to guarantee a value in a specific position – see bellow.-
ACP can also provide with tapers with different slopes, with areas with constant value or jumps, according to customer’s specifications.
Special tapers can be combined with physical detents to match the areas where the customer wants to guarantee a constant value with a particular angular position. This is particularly suitable in applications which can benefit from a feeling of maintained control over the position, for example, regulation of temperature or speed.

#### Linearity

The term “linearity” implies that the real law obtained from plotting angular position vs voltage output is compared  with a straight line.
Independent linearity (LN)
It is the maximum vertical deviation of the real law from the straight reference line chosen to best minimize the distance from the real line in any position.
It is expressed as a percentage of the total voltage applied.
In the graph below, “K” would be the maximum independent linearity and “k” the line with which the real law is compared.
Absolute Linearity (LA)
It is the maximum vertical deviation of the real law from the straight reference line that runs through specified minimum and maximum points.
These points would be zero and 100% of the maximum applied voltage.
In the graph below, “H” would be the maximum absolute linearity of the real law and “h” the theoretical line with which the real line is compared. When some customers are looking for correspondence of angle and value, this is the concept to consider.

##### Recommended soldering conditions

Soldering conditions (Lead free, RoHS compliant)*

Manual Soldering Reflow soldering SMD Flow (wave) soldering
Soldering tools of 20W max. Preheating temperature: Max 150ºC; 60-90 s Recommended Alloy: SnAgCu
Maximum temperature of soldering tools: 280ºC Temperature Ramp-up: 2-3ºC / s. Preheating stage: Max 100ºC; 30-60 s.
Time: 3 s. max. Over 220ºC:<40 s. Temperature Ramp-up:1.2-2.5ºC/s.
Solder temperature: 240ºC for 5 ± 1 s. Max. wave temp.: 260ºC for 4s.,
(245ºC recommended)
Besides recommended conditions,
ACP SMD potentiometers have successfully
passed IEC 60068-2-58 tests.
Time within +0º-10ºC of peak: 10s.
Cooling rate: 5ºC/s.