NEG-OUT
IEC logic negation at output
Circle on an output edge meaning the internal 1 state of the element produces an external 0.
IEC
IEC · NEG-IN
IEC logic negation at input
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.
- 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.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · 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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · NEG-IN
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.
A distinction that matters
The polarity indicator triangle states an active-low level directly and does not depend on a declared logic convention.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
Defines logic negation at an input and its relation to logic conventions.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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