# IEC logic negation at input

Canonical URL: https://eloragrid.ai/symbols/iec-logic-input-negation
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: NEG-IN
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Small circle at the input edge of the outline
Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier.

Small circle where an input meets an outline: an external 0 produces the internal 1 (active) state.

## In plain English

### What does IEC logic negation at input mean?

The negation circle at an input means that the external 0 state produces the internal 1 state of the element. It is a pure logic statement: to relate it to voltage levels, the drawing must declare positive or negative logic. TI's public overview notes that this is the older form, with the polarity triangle now preferred in device data books.

### A simple example

On functional logic diagrams for control systems, input negation is a compact way to show normally-closed or fault-healthy signals entering a gate without drawing a separate inverter. The reader should confirm the declared logic convention before relating a circle to a contact state or voltage.

### What the drawings help you do

A negation circle does not specify how the inversion is implemented. It may be a separate inverter, an internal feature of the device, or a negated contact in a PLC rung.

### This particular reference

Small circle where an input meets an outline: an external 0 produces the internal 1 (active) state. The polarity indicator triangle states an active-low level directly and does not depend on a declared logic convention.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Rating: A value stating the conditions for which equipment is specified.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)


## What it represents

The negation circle at an input means that the external 0 state produces the internal 1 state of the element. It is a pure logic statement: to relate it to voltage levels, the drawing must declare positive or negative logic. TI's public overview notes that this is the older form, with the polarity triangle now preferred in device data books.
On functional logic diagrams for control systems, input negation is a compact way to show normally-closed or fault-healthy signals entering a gate without drawing a separate inverter. The reader should confirm the declared logic convention before relating a circle to a contact state or voltage.
A negation circle does not specify how the inversion is implemented. It may be a separate inverter, an internal feature of the device, or a negated contact in a PLC rung.

## How to read it

- Check the sheet note for positive or negative logic.
- Do not confuse the circle with a connection dot or terminal.

## Information to show or reference

- Draw the circle touching the outline.
- Declare the logic convention on the drawing.
- Avoid mixing negation circles and polarity triangles on one sheet.

## Important distinction

The polarity indicator triangle states an active-low level directly and does not depend on a declared logic convention.

## Facts

- Meaning: External 0 produces internal 1
- Dependency: Needs a declared logic convention to map to levels
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Defines logic negation at an input and its relation to logic conventions.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.