Trimpot / Trimmer Symbol
Definition: The Trimpot / Trimmer symbol represents a miniature, board-mounted variable resistor used for one-time or infrequent circuit calibration, standardised under IEC 60617-04 and ANSI Y32.2 / IEEE 315, with three terminals: A (end 1), B (end 2), and W (wiper), providing an adjustable resistance between 0 Ω and the full rated value.
Also known as: trimmer potentiometer, preset potentiometer, trimmer resistor, preset resistor, calibration potentiometer.
What the Trimpot / Trimmer symbol means
The Trimpot / Trimmer symbol represents a small variable resistor designed to be soldered directly onto a printed circuit board and adjusted with a screwdriver during calibration, rather than being operated continuously by hand. Its adjustable wiper contact slides along a resistive track between two fixed end terminals, allowing a technician to set a precise resistance or voltage divider ratio when the circuit is first commissioned.
In schematic diagrams, the trimpot symbol signals that a particular node voltage, gain, or timing constant requires fine-tuning to meet a specification. Unlike a full-size potentiometer — which is adjusted frequently by a user — the trimmer is typically set once and then left undisturbed for the life of the product. Common applications include zero-offset adjustment of op-amp circuits, gain calibration of sensor amplifiers, and frequency trim of oscillators.
How to identify the Trimpot / Trimmer symbol
The Trimpot / Trimmer symbol uses the same base as a standard variable resistor: in IEC style it is drawn as a small rectangle (representing a fixed resistor) with an arrow through or across it indicating the adjustable wiper; in ANSI style the base is a zigzag line with an arrow. The wiper connection (W) exits the symbol from the midpoint arrow — often shown as a short line ending in a dot or arrow pointing at the centre of the resistive element. The presence of three terminals (A, W, B) and the adjustment arrow distinguishes a trimpot from a two-terminal rheostat.
Function in a circuit
A trimpot functions as a voltage divider or variable resistance in a circuit: connecting the wiper (W) between the two end terminals (A and B) gives a voltage output proportional to wiper position; connecting one end terminal and the wiper gives a two-terminal variable resistance from 0 Ω to the full resistance value. Because the element is sealed and typically accessed only via a screwdriver slot or a small shaft, it is well-suited to factory or field calibration where inadvertent adjustment by end-users is undesirable. Trimpots are manufactured in single-turn and multi-turn (cermet, wirewound) variants to suit required precision.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 (passive components): the trimmer potentiometer is drawn as a rectangle (resistor body) with a diagonal arrow through it representing the wiper; terminals labelled 1, 2 (end terminals) and the arrow connection as the wiper. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315: the same component is shown as a zigzag line (ANSI resistor symbol) with an adjustable-tap arrow pointing at the zigzag; three terminals are used for potentiometer mode or two for rheostat mode. Designator: R or VR. |
| Key difference | IEC uses a filled rectangle for the resistor body; ANSI uses a zigzag line. Both use an arrow to indicate the movable wiper. The schematic designator is R (or VR for variable resistor) in both standards. |
Terminals / pins
| Pin | Name |
|---|---|
| a | A |
| b | B |
| wiper | W |
Typical values
Common resistance values: 100 Ω, 500 Ω, 1 kΩ, 5 kΩ, 10 kΩ, 50 kΩ, 100 kΩ, 1 MΩ. Power ratings: typically 0.1 W to 0.5 W. Resistance tolerance: ±20–30% on full value; resolution limited by turns (single-turn ~10%, multi-turn <1%). Temperature coefficient: 50–200 ppm/°C for cermet types.
Where the Trimpot / Trimmer symbol is used
- Zero-offset and gain calibration of operational amplifier instrumentation circuits
- Frequency trimming of RC oscillators and crystal oscillator load circuits
- Bias point adjustment in RF amplifier and transistor bias networks
- Contrast and brightness adjustment on LCD display drive boards
- Threshold voltage setting for comparator and Schmitt trigger circuits
- Balance trimming in Wheatstone bridge sensor circuits
- Output voltage fine adjustment on linear and switching power supplies
Example
In a precision strain-gauge amplifier, a 10 kΩ multi-turn cermet trimpot connected between the INA128 instrumentation amplifier's reference pin and ground allows a technician to null the output offset voltage to within 1 mV during factory calibration — its symbol appearing on the schematic with the wiper (W) connected to the REF pin and one end (A) to ground.
Key facts
- The Trimpot / Trimmer symbol is a variable resistor (IEC rectangle or ANSI zigzag) with an adjustable wiper arrow, three terminals: A (end 1), B (end 2), and W (wiper).
- Reference designator: R or VR (variable resistor); IEC 60617-04 and ANSI Y32.2 / IEEE 315 both define the symbol.
- A trimpot is designed for infrequent screwdriver adjustment, not continuous user operation — distinguishing it from a panel-mount potentiometer.
- In potentiometer (voltage divider) mode all three terminals are used; in rheostat mode only the wiper (W) and one end terminal (A or B) are connected.
- Common full-resistance values range from 100 Ω to 1 MΩ; power ratings are typically 0.1–0.5 W.
- Multi-turn cermet trimpots offer 10–25 turns for fine resolution; single-turn types are smaller but less precise.
- The schematic wiper arrow points at the resistive element (rectangle or zigzag), visually conveying that its position along the track is adjustable.
- Failing to connect one end terminal in rheostat mode (leaving it floating) risks open-circuit on the wiper track if the wiper loses contact — best practice is to tie the unused end to the wiper pin.
Frequently asked questions
What does the trimpot symbol look like?
The trimpot symbol shows a resistor body — a rectangle in IEC 60617 or a zigzag in ANSI Y32.2 — with a diagonal arrow pointing at or through the centre of the resistor element to represent the movable wiper. Three terminals exit the symbol: one from each end of the resistor body (A and B) and one from the wiper arrow tip (W).
What does the trimpot symbol mean in a circuit?
The trimpot symbol means a small, board-mounted variable resistor is present at that location, used to calibrate or fine-tune a circuit parameter such as gain, offset, threshold, or frequency. It is adjusted with a screwdriver, typically once during manufacturing or commissioning, and is not intended for regular end-user adjustment.
What is the difference between a trimpot and a potentiometer symbol?
Both symbols show a variable resistor with three terminals and a wiper arrow. A standard potentiometer symbol represents a component with a rotary or slider shaft for continuous user adjustment, whereas a trimpot symbol specifically represents a miniature preset component for infrequent calibration. In practice, the glyph is identical; the distinction is implied by the part type annotated in the bill of materials.
What is the designator letter for a trimpot on a schematic?
The reference designator for a trimpot is R (general resistor series) or VR (variable resistor), depending on the schematic convention. Both IEC 60617-04 and ANSI Y32.2 / IEEE 315 use R as the standard designator for resistors including variable types; VR is a common informal convention for variable resistors.
What are the three terminals of a trimpot symbol?
The three terminals are A (end terminal 1 of the resistive track), B (end terminal 2 of the resistive track), and W (wiper — the movable contact). Connecting A to one supply voltage and B to another, then reading W, gives a voltage proportional to wiper position. Connecting only A and W (or B and W) gives a two-terminal variable resistance.
What is the IEC vs ANSI difference for the trimpot symbol?
In IEC 60617-04, the resistor body is a filled rectangle; in ANSI Y32.2, it is a zigzag line. Both standards add a diagonal adjustable arrow to indicate the wiper. The meaning and terminal count are identical; only the resistor body shape differs between the two regional standards.
What standard defines the trimpot symbol?
The trimpot / trimmer potentiometer symbol is defined in IEC 60617-04 (passive components, resistors) and ANSI Y32.2 / IEEE 315-1975. Both standards classify it as an adjustable (variable) resistor with the rectangle (IEC) or zigzag (ANSI) body and an arrow for the wiper contact.
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