Wheatstone Bridge Symbol

Definition: The Wheatstone Bridge symbol represents a four-resistor diamond-shaped measurement circuit used in schematic diagrams to denote a balanced bridge configuration that determines an unknown resistance or converts a small resistance change—such as from a strain gauge, RTD, or thermistor—into a measurable differential voltage across the Sense+ and Sense− output terminals.

Also known as: Wheatstone bridge circuit, resistance bridge, strain gauge bridge, bridge circuit, four-arm bridge, balanced bridge.

What the Wheatstone Bridge symbol means

The Wheatstone Bridge symbol identifies a precision measurement network consisting of four resistors arranged in a diamond (rhombus) topology. A supply voltage V+ is applied between the top and bottom nodes, and the differential output voltage appears between the left (Sense+) and right (Sense−) nodes. When all four resistors are perfectly matched, the bridge is balanced and the output is zero; any imbalance caused by a change in one or more resistor values produces a proportional differential voltage.

In circuit diagrams the symbol marks a measurement subsystem that converts a physical quantity—strain, temperature, pressure, or displacement—into an electrical signal. One or more of the bridge arms is replaced by a sensing element (strain gauge, thermistor, RTD) whose resistance varies with the measured quantity. The differential output is then amplified, typically by an instrumentation amplifier, to produce a usable signal.

How to identify the Wheatstone Bridge symbol

The symbol is drawn as a diamond outline with four nodes at the top (V+), bottom (GND), left (Sense+), and right (Sense−). Each of the four sides of the diamond represents one resistor arm of the bridge. The top node connects V+ through the upper two arms, and the bottom node connects GND through the lower two arms. This diamond shape clearly distinguishes it from other multi-resistor network symbols.

Function and usage boundary

A Wheatstone Bridge operates on the principle of voltage division: two resistor dividers share a common supply, and the differential voltage between their midpoints is zero when the ratio of adjacent resistors is equal. When a sensor element in one arm changes its resistance by ΔR, the bridge output becomes approximately (ΔR/4R) × Vcc for a quarter-bridge configuration, providing high sensitivity to small resistance changes while rejecting common-mode supply noise. Full-bridge configurations (all four arms active) provide four times the sensitivity of a quarter-bridge.

Standards: IEC vs ANSI

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Logical terminals

Where the Wheatstone Bridge symbol is used

• Strain gauge load cells in weighing scales, force sensors, and torque transducers
• Pressure transducers where piezoresistive elements form one or more bridge arms
• RTD temperature measurement circuits using a precision bridge for linearisation
• Whetstone bridge sensors in automotive manifold absolute pressure (MAP) sensors
• Precision resistance measurement instruments and LCR meters
• Biomedical force and strain sensing in prosthetics and surgical robotics

Key facts

• The Wheatstone Bridge symbol has four pins: V+ (excitation positive), GND (excitation negative), Sense+ (output positive), and Sense− (output negative).
• The bridge is balanced (zero differential output) when R1/R2 = R4/R3; any deviation from this ratio produces a differential output voltage proportional to the imbalance.
• A quarter-bridge has one variable (sensing) arm; a half-bridge has two; a full-bridge has all four arms as sensing elements—full-bridge provides the highest sensitivity and best temperature compensation.
• Standard strain-gauge bridge resistances are 120 Ω, 350 Ω, and 1000 Ω; 350 Ω is the most common in industrial load cells.
• The typical full-scale bridge output sensitivity is 1–4 mV/V (millivolts of output per volt of excitation), requiring amplification by a factor of 100–1000 before A/D conversion.
• The Wheatstone Bridge was mathematically described by Charles Wheatstone in 1843, though it was invented by Samuel Hunter Christie in 1833.
• Long cable runs between a bridge sensor and its amplifier should use six-wire (Kelvin) connections to eliminate lead-resistance errors in precision measurements.

Frequently asked questions

What does the Wheatstone Bridge symbol mean in a circuit diagram?

The Wheatstone Bridge symbol represents a four-resistor diamond network used to measure small changes in resistance. In a circuit diagram it identifies a measurement subsystem where one or more resistor arms are sensing elements (strain gauges, thermistors, or RTDs) whose resistance change produces a differential output voltage at the Sense+ and Sense− terminals.

What does the Wheatstone Bridge symbol look like?

The symbol is drawn as a diamond with four nodes: V+ at the top, GND at the bottom, Sense+ on the left, and Sense− on the right. Each of the four diamond sides represents one resistor arm. IEC diagrams use rectangular resistor glyphs on each arm; ANSI diagrams use zigzag resistor glyphs.

What are the four pins of the Wheatstone Bridge symbol?

The four pins are V+ (positive excitation supply), GND (negative excitation supply), Sense+ (differential output positive), and Sense− (differential output negative). The supply pins drive the bridge and the sense pins connect to a differential amplifier or instrumentation amplifier.

What is the difference between a quarter-bridge, half-bridge, and full-bridge?

A quarter-bridge has one active sensing element and three fixed resistors; a half-bridge has two active elements (typically in adjacent or opposite arms); a full-bridge has all four arms as active sensors. Full-bridge configuration gives four times the output of a quarter-bridge and also compensates for temperature-induced resistance changes in the sensing elements.

What is the standard resistance value for a Wheatstone bridge in load cells?

The most common standard strain-gauge bridge resistance is 350 Ω, though 120 Ω and 1000 Ω bridges are also widely used. Higher resistance values reduce self-heating in the strain gauges and allow longer cable runs without significant lead-resistance errors.

What amplifier is used with a Wheatstone Bridge output?

An instrumentation amplifier (in-amp), such as the INA128 or AD620, is the standard choice for amplifying Wheatstone bridge output. Instrumentation amplifiers provide high common-mode rejection (>80 dB), programmable gain via a single resistor, and high input impedance so they do not load the bridge.

What standard defines the Wheatstone Bridge schematic symbol?

Neither IEC 60617 nor ANSI Y32.2/IEEE 315 defines a dedicated symbol for the complete Wheatstone bridge. It is drawn using standard resistor symbols (IEC rectangle or ANSI zigzag) arranged in a diamond topology, with the bridge function identified by a surrounding box label.

Related symbols

• Current Sensor (ACS712) symbol
• Ammeter symbol
• Current Transformer (CT) symbol
• Load Cell (HX711) symbol
• Test Point symbol
• Wire Crossing (No Connection) symbol

Physical breadboard, PCB, and panel mapping

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