# IEC summing amplifier element (Σ)

Canonical URL: https://eloragrid.ai/symbols/iec-summing-amplifier
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: Σ
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Rectangular analogue element with Σ function and several weighted inputs
IEC-style rectangular analogue element presentation; the IEC graphical symbols programme is cited for context only. Independent educational drawing; not certified IEC geometry or an IEC database identifier.

Analogue element with Σ and several inputs, producing an output proportional to the weighted sum of the inputs.

## In plain English

### What does IEC summing amplifier element (Σ) mean?

A summing amplifier adds several analogue inputs, each with its own weighting. In IEC-style analogue element diagrams it is drawn as a rectangle with an amplifier mark and the Σ function, with weighting factors written next to each input. The usual circuit realisation is an inverting op-amp with one input resistor per signal.

### A simple example

Summers appear in control loops for combining set-point and feedforward signals, in audio-style mixing of measurements, and in analogue computation. The weighting factors and the sign of the output must be stated because an inverting realisation reverses polarity.

### What the drawings help you do

The element does not show the resistor network that sets the weights. For a construction schematic, the op-amp circuit with values should be drawn or referenced.

### This particular reference

Analogue element with Σ and several inputs, producing an output proportional to the weighted sum of the inputs. The digital Σ adder adds binary words; the analogue summing element adds voltages or currents.

### Terms

- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic: A drawing showing function and connections rather than physical appearance.

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.

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)
- [University tutorials: amplifier configurations and signal processing](https://wiki.analog.com/university/courses/tutorials/index)


## What it represents

A summing amplifier adds several analogue inputs, each with its own weighting. In IEC-style analogue element diagrams it is drawn as a rectangle with an amplifier mark and the Σ function, with weighting factors written next to each input. The usual circuit realisation is an inverting op-amp with one input resistor per signal.
Summers appear in control loops for combining set-point and feedforward signals, in audio-style mixing of measurements, and in analogue computation. The weighting factors and the sign of the output must be stated because an inverting realisation reverses polarity.
The element does not show the resistor network that sets the weights. For a construction schematic, the op-amp circuit with values should be drawn or referenced.

## How to read it

- Weighting factors are written beside the inputs.
- An inverting realisation gives a negative sum unless followed by an inverter.

## Information to show or reference

- State each input weight.
- State output sign.
- Reference the implementing op-amp circuit.

## Important distinction

The digital Σ adder adds binary words; the analogue summing element adds voltages or currents.

## Facts

- Function: Weighted sum of inputs
- Typical realisation: Inverting op-amp with one resistor per input
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC graphical symbols programme covering analogue elements; no geometry reproduced.
- [University tutorials: amplifier configurations and signal processing](https://wiki.analog.com/university/courses/tutorials/index) — Analog Devices. Public tutorial material on op-amp configurations including summing circuits.

## 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.