What is mV/V Output in a Load Cell? Understanding Load Cell Sensitivity and Excitation Voltage
When selecting a load cell, one of the most important specifications you will come across is mV/V, such as 1 mV/V, 2 mV/V or 3 mV/V.
But what does mV/V actually mean?
Unlike a conventional pressure transmitter or temperature transmitter that may provide a 4–20 mA or 0–10 V output, a load cell typically produces a very small electrical signal in the millivolt range.
The output is specified in millivolts per volt (mV/V) because the load-cell output depends on the excitation voltage supplied to it.
What does 2 mV/V mean?
Suppose a load cell has a sensitivity of:2 mV/V
This means that at its rated full-scale load, the load cell produces approximately 2 mV of output for every 1 V of excitation.
For example:
Excitation Voltage | Full-Scale Output |
5 V | 10 mV |
10 V | 20 mV |
12 V | 24 mV |
The calculation is:
Full-Scale Output = Load Cell Sensitivity × Excitation Voltage
Therefore:
2 mV/V × 10 V = 20 mV
A 1000 kg load cell with 2 mV/V sensitivity and 10 V excitation will produce approximately 20 mV at 1000 kg.
Why does the output depend on excitation voltage?
A typical strain-gauge load cell uses a Wheatstone bridge.
Several strain gauges are bonded to the load-cell's elastic element. When a force is applied, the element deforms slightly. This deformation causes changes in the resistance of the strain gauges.
The gauges are connected in a bridge arrangement.
When there is no load, the bridge is ideally balanced and the differential output is close to zero.
When a load is applied, the resistance of the strain gauges changes. This unbalances the bridge and produces a small differential voltage.
The excitation voltage provides the electrical energy for this bridge.
Therefore, increasing the excitation voltage also increases the bridge's output voltage.
This is why load-cell sensitivity is expressed as mV/V rather than simply mV.
Is the load-cell output linear?
Ideally, the output is proportional to the applied load.
For a 2 mV/V load cell with 10 V excitation, the full-scale output is approximately 20 mV.
Therefore:
Applied Load | Approx. Output |
0% | 0 mV |
25% | 5 mV |
50% | 10 mV |
75% | 15 mV |
100% | 20 mV |
This represents the ideal relationship.
In a real load cell, the output will have small deviations from perfect linearity. Manufacturers therefore specify parameters such as non-linearity, hysteresis, repeatability and zero balance.
Why is mV/V used instead of a fixed mV output?
Consider two identical 2 mV/V load cells.
If one is powered with 5 V:
2 mV/V × 5 V = 10 mV
If the other is powered with 10 V:
2 mV/V × 10 V = 20 mV
The load-cell sensitivity remains 2 mV/V, even though the actual output voltage is different.
This makes mV/V a useful way of specifying the performance of the load cell independently of a particular excitation voltage.
What happens if the excitation voltage changes?
This is an important consideration when designing a weighing or force-measurement system.
Suppose a 2 mV/V load cell is operating with 10 V excitation.
At full load:
2 × 10 = 20 mV
If the excitation falls to 9 V:
2 × 9 = 18 mV
The same mechanical load now produces a different electrical output.
Therefore, a stable excitation supply is important for accurate measurement.
Many load-cell instruments and transmitters use a ratiometric measurement approach, where the excitation voltage is also used as a reference. This helps reduce errors caused by changes in excitation voltage.
Why is the load-cell signal so small?
A load cell is designed to measure very small physical deformation.
As a result, its electrical output is also very small—often only a few millivolts at full scale.
For example:
2 mV/V × 10 V = 20 mV
This is much smaller than the signals normally used by industrial control systems.
Therefore, a load cell is commonly connected to a load-cell amplifier, indicator or transmitter.
The signal can then be converted into an industrial output such as:
mV/V → 0–10 V
or
mV/V → 4–20 mA
or a digital communication signal.
Example: Selecting an amplifier
Consider a 2000 kg load cell with:
Capacity: 2000 kg
Sensitivity: 2 mV/V
Excitation: 10 V
The full-scale bridge output is:
2 mV/V × 10 V = 20 mV
The amplifier therefore needs to accept a load-cell input around 0–20 mV (with appropriate allowance for zero offset and the manufacturer's specified input range).
If the application requires a 4–20 mA output, the transmitter can scale:
0 kg → 4 mA
1000 kg → 12 mA
2000 kg → 20 mA
This allows the very small load-cell signal to be integrated with conventional industrial PLCs, controllers and data-acquisition systems.
Key points to remember
mV/V is the sensitivity of a load cell.
A 2 mV/V load cell produces approximately:
2 mV output for every 1 V of excitation at full load.
Therefore:
Output = mV/V × Excitation Voltage × Load %
For example:
2 mV/V × 10 V × 50% = 10 mV
The output is approximately linear with load, but real-world load cells have small errors that are specified in their datasheets.
Understanding mV/V is therefore essential when selecting a load cell, excitation supply, load-cell amplifier or 4–20 mA transmitter.
Need help selecting a load cell?
Trias Automation provides solutions for force and load measurement, including load cells and signal-conditioning solutions for industrial applications.
If you are unsure about the required capacity, mV/V sensitivity, excitation voltage or output signal, the correct combination of load cell and transmitter should be selected based on the application requirements.
Comments