4-Wire Load Cell Wiring Diagram: Wheatstone Bridge, EXC+/EXC-/SIG+/SIG- Connections & mV/V Output

4-Wire Load Cell Wiring Diagram: Wheatstone Bridge, EXC+/EXC-/SIG+/SIG- Connections & mV/V Output — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable 4 wire load cell wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

Connect a 4-wire load cell correctly — excitation supply, differential signal output, and amplifier interface — to get accurate, stable weight measurements from a Wheatstone bridge sensor.

A load cell converts mechanical force into an electrical signal using the piezo-resistive effect. Inside the load cell body, four strain gauges are bonded to a machined metal flexure and electrically connected in a Wheatstone bridge configuration. This arrangement provides temperature compensation and a differential output signal that is immune to common-mode noise — both critical for accurate weighing in industrial environments.

The four wires on a standard load cell carry two electrically distinct signals. The excitation pair — labelled EXC+ (or E+, VCC, or red) and EXC- (or E-, GND, or black) — supplies a stable reference voltage to the bridge, typically 5V or 10V DC from a regulated source. The signal pair — labelled SIG+ (or S+, OUT+, or white/green) and SIG- (or S-, OUT-, or blue) — carries the differential output voltage generated by the bridge imbalance when the load cell is under load.

At zero load, a perfectly balanced bridge outputs 0 mV differential (in practice, a small offset due to manufacturing tolerances). Under rated load, the bridge outputs a voltage expressed as millivolts per volt of excitation — typically 1 mV/V to 3 mV/V. This means a load cell with a 2 mV/V rating, excited at 10V, outputs 20 mV at full rated load. This small signal must be amplified before it can be read by a microcontroller ADC or display module.

For 4-wire connections specifically, the excitation voltage is measured and regulated at the instrument end — the instrument does not independently measure the voltage actually arriving at the load cell. This is the key limitation of a 4-wire configuration: if the excitation cable has resistance, the actual voltage at the bridge is lower than the nominal excitation, introducing a systematic error. For run lengths above approximately 3 metres or where cable resistance is not negligible, a 6-wire (sense wire) connection is preferred, as the sense wires allow the instrument to correct for this drop.

The amplifier or signal conditioner must accept a differential millivolt input. Dedicated load cell amplifier ICs (such as the HX711 — a common 24-bit delta-sigma ADC bridge amplifier) are widely used in embedded systems. Instrumentation amplifiers with adjustable gain are used in industrial signal conditioners. The output of the amplifier may be a voltage (0–5V, 0–10V), a current (4–20 mA), or a digital value via I2C, SPI, or RS-485.

How to wire 4 wire load cell wiring diagram

Identify wire colours on your specific load cell Do not rely on generic colour conventions. Obtain the datasheet or wiring diagram for your exact load cell model. Common conventions are: red = EXC+, black = EXC-, white or green = SIG+, blue or yellow = SIG-. Some manufacturers use green/white/red/black or other combinations. If the datasheet is unavailable, use a multimeter in resistance mode to identify the bridge — EXC+ to EXC- and SIG+ to SIG- pairs will each read the bridge nominal resistance (commonly 350 Ω or 1 000 Ω), while EXC+ to SIG+ will read approximately half the bridge resistance.
Prepare the cable and protect the junction If extending the load cell cable, use shielded twisted-pair cable with the same or larger conductor cross-section. Match the conductor colours or label each wire clearly at both ends before cutting. Strip no more than 8 mm of insulation per wire — excess exposed conductor near a millivolt-level circuit increases noise pickup. Solder all joins, do not rely on push-in or butt splice connectors for signal wires in a precision application.
Connect excitation wires to regulated power supply Connect EXC+ to the positive terminal of your regulated 5V or 10V excitation supply, and EXC- to the supply negative (ground). Use a dedicated, low-noise regulated supply — never power the load cell excitation from a switching power supply shared with motors, relays, or other noisy loads without adequate filtering. Measure the actual excitation voltage at the load cell terminals (not at the supply output) and record this value — it is used in calibration.
Connect signal wires to amplifier or signal conditioner Connect SIG+ to the INA+ (or IN+, E+) input of your amplifier module. Connect SIG- to the INA- (or IN-, E-) input. If using a HX711-type amplifier module, connect E+ to SIG+ and E- to SIG-. Verify the amplifier's input voltage range accommodates the expected full-scale signal (for example, ±20 mV for a 2 mV/V cell at 10V excitation). Keep signal wire routing as short as practical and away from power wires.
Set amplifier gain and reference For most embedded applications with a 24-bit ADC amplifier, select a gain of 128 (for 2.5 mV/V or less full-scale signal at 5V excitation) or 64 (for higher excitation voltages). Set the amplifier's voltage reference to match the excitation voltage where applicable. Confirm the amplifier can resolve your required weight resolution — a 24-bit ADC provides approximately 16 million counts over the full range, far exceeding the load cell's mechanical accuracy.
Shield and route cables to minimise noise Use the cable shield (if present) and connect it to ground at the instrument end only — not at the load cell end. Grounding the shield at both ends creates a ground loop. Route signal cables away from AC mains wiring, motor drives, and relay coils. If the installation environment has significant EMI, use shielded twisted pair throughout and add a small ceramic capacitor (100 nF) across each of the four terminals at the amplifier input as an RF filter.
Calibrate with known reference weights With zero load applied, record the amplifier output (zero offset). Apply a known reference weight that is at least 25% of the rated capacity (preferably 50–100%). Record the output. Calculate the span: (output at known weight - zero offset) / known weight = counts per unit. Verify linearity with at least two further reference weights across the range. If the load cell is operating in a temperature-varying environment, perform calibration at the expected operating temperature.

Specifications

Bridge configuration	Full Wheatstone bridge, four active strain gauge arms
Standard excitation voltage	5V DC or 10V DC (regulated, low-ripple)
Typical full-scale output	1–3 mV/V (e.g., 10–30 mV at 10V excitation)
Bridge resistance (common values)	350 Ω or 1 000 Ω (nominal, balanced bridge)
Number of wires — standard configuration	4 (EXC+, EXC-, SIG+, SIG-); 6-wire adds remote sense pair
Signal cable recommended type	Shielded twisted-pair, 24 AWG (0.2 mm²) minimum
Maximum recommended excitation cable resistance (4-wire)	Less than 1 Ω total (EXC+ and EXC- combined) for <0.1% error
Typical amplifier resolution (embedded use)	24-bit delta-sigma ADC; effective noise-free resolution approximately 16–18 bits

Safety warnings

Load cells are precision instruments sensitive to overload. Applying force beyond the rated capacity — even momentarily — plastically deforms the flexure element and permanently alters the calibration. Always design the mechanical system to limit maximum possible load to no more than 150% of the rated capacity, and use mechanical overload stops where feasible.
The signal output of a load cell (millivolts range) is not a hazardous voltage. However, if the load cell is installed in an industrial setting with AC-powered equipment nearby, ensure that mains voltage cannot appear on the load cell body or cables through insulation failure. Use an isolation barrier if the load cell mechanical structure is connected to plant equipment with mains wiring.
Do not apply the excitation voltage across the signal output terminals. EXC+ and EXC- are connected to the bridge; SIG+ and SIG- measure a fraction of that bridge voltage. Applying excitation directly to SIG terminals will not damage the wiring (the voltages are the same) but will not produce a useful signal — and applying any voltage significantly above the rated excitation to any terminal risks burning out the precision thin-film resistors inside the load cell.
When mounting a load cell, apply force only along the intended axis. Off-axis loading (bending moments, side loads, or torsion) introduces measurement error and, in severe cases, permanently damages the flexure. Follow the manufacturer's mounting instructions precisely — load cell accuracy is as dependent on mechanical installation as on electrical connection.

Tools needed

Digital multimeter with millivolt resolution (for signal measurement) and resistance mode (for bridge identification)
Regulated bench power supply (5V or 10V, adjustable, with current limiting)
Soldering iron and solder (for signal wire joins)
Heat-shrink tubing and heat gun
Small flat-blade and Phillips screwdrivers (for terminal blocks)
Calibrated reference weights (minimum 2 weights covering 25% and 100% of rated capacity)
Cable tie and mounting hardware

Common mistakes

Swapping EXC and SIG wires. Connecting the excitation supply to the signal terminals produces no output signal and may damage the amplifier input if the excitation voltage exceeds the amplifier's input common-mode range. Always verify wire identification against the datasheet before applying power.
Using an unregulated or switch-mode power supply without filtering for excitation. Load cell output is directly proportional to excitation voltage. A power supply with 1% ripple introduces 1% measurement noise before any other error source is considered. Use a well-regulated linear supply or a switching supply followed by an LC or RC filter stage.
Grounding the cable shield at both ends. A shield grounded at both the load cell end and the instrument end forms a loop antenna that actively introduces mains-frequency noise into the signal. Ground the shield at the instrument (amplifier) end only, leaving the load cell end floating.
Ignoring the effect of cable resistance on 4-wire accuracy. In a 4-wire configuration, the instrument does not compensate for excitation voltage drop in the cable. A 10-metre run of 24 AWG cable (approximately 0.84 Ω/metre) introduces about 16 Ω of resistance in the excitation supply. If this causes the bridge excitation to drop from 10.00V to 9.87V, every reading will be 1.3% low — systematic and invisible without the 6-wire sense connection.
Not zero-ing the system with the full mechanical structure in place. The load cell output at zero weight includes the weight of any platform, mounting hardware, and cables attached to it. Always tare with everything except the load to be measured in place, not with a bare load cell.
Applying load cell readings in high-vibration environments without filtering. Mechanical vibration creates real force fluctuations that the load cell accurately measures. If you need a steady weight reading in a vibrating environment, implement a software moving-average or low-pass filter at the amplifier output stage — do not simply try to reduce amplifier gain to mask the noise.

Troubleshooting

Load cell output is zero regardless of applied load: Cause: EXC and SIG wires are swapped (no excitation across the bridge so no signal change with load), the excitation supply is not connected or is not active, or the amplifier gain is set to zero or the amplifier input is saturated Fix: Measure voltage across EXC+ and EXC- at the load cell terminals — should equal nominal excitation (5V or 10V). Measure voltage across SIG+ and SIG- — should be a small offset from zero at no load and should change (even by a fraction of a millivolt) when slight force is applied. If excitation is correct and SIG changes with load, the amplifier connection or gain setting is the fault.
Output reading is noisy and unstable even without load changes: Cause: Electrical noise from nearby AC equipment, an unfiltered switching power supply on the excitation rail, or a cable shield grounded at both ends creating a ground loop Fix: Measure excitation voltage ripple with the multimeter in AC mode — any reading above 1 mV RMS suggests supply noise. Add RC filtering on the excitation rail. Check shield grounding — disconnect the shield at the load cell end and measure noise improvement. Route signal cables away from AC mains and motor drives. Add 100 nF ceramic bypass capacitors across the signal input terminals at the amplifier.
Reading is consistently offset or reads wrong full-scale value: Cause: The system has not been calibrated with the actual excitation voltage in use, or the load cell sensitivity (mV/V) assumed in calibration does not match the actual device Fix: Re-measure the actual excitation voltage at the load cell terminals (not at the supply). Obtain the load cell datasheet and confirm the rated sensitivity in mV/V. Re-calibrate using a two-point method: zero-load offset first, then apply a known reference weight and adjust the span coefficient until the reading matches. Do not trust default calibration values — always calibrate with reference weights.

Frequently asked questions

What do the four wires on a load cell connect to?

EXC+ (red) and EXC- (black) connect to the regulated excitation voltage supply (typically 5V or 10V DC). SIG+ (white or green) and SIG- (blue or yellow) connect to the differential signal input of the amplifier or signal conditioner. Never apply the excitation voltage directly to the signal inputs — the signal output is only millivolts and cannot drive a load. Always check your specific load cell's datasheet for colour coding, as it varies by manufacturer.

What is mV/V sensitivity in a load cell?

mV/V (millivolts per volt) is the full-scale output of the load cell divided by the excitation voltage. A 2 mV/V load cell at 10V excitation outputs 20 mV at its rated maximum load. At half rated load, it outputs 10 mV. This ratio is constant for a given excitation voltage, which is why a stable, regulated excitation supply is essential — any variation in excitation directly and proportionally varies the output reading.

When should I use 6-wire instead of 4-wire connection?

Use 6-wire (remote sense) when cable length between the instrument and load cell exceeds approximately 3 metres, when cables pass through an environment with temperature swings, or when the cable conductor resistance is not negligible compared to the accuracy required. The two additional sense wires allow the instrument to measure the actual voltage at the load cell terminals and compensate for cable resistance drop in the excitation feed.

Why does my load cell output drift over time?

Common causes: an unstable or unregulated excitation supply (mains hum, ripple, or thermal variation); mechanical creep in the load cell flexure from sustained over-load or off-axis loading; temperature effects on the bridge resistances if the load cell is not temperature-compensated for your operating range; or poor quality cable connections introducing contact resistance that changes with temperature and vibration. Isolate each cause methodically by testing with a known stable excitation source first.

Can I connect multiple load cells together?

Yes — multiple load cells can be wired in parallel (a summing junction box connects all excitation wires together and all signal wires together) to create a multi-point weighing platform. All load cells in a parallel array must have the same nominal resistance and sensitivity (mV/V) rating to share the load correctly. The combined output sensitivity is the same mV/V as a single cell, but the system capacity is the sum of all cells' rated capacities.

Related diagrams

Free electrical calculators

Edit this diagram free in the online editor