Ratiometric output is a voltage output from the Sensor that is proportional to the supply voltage. The output voltage is a percentage of the supply voltage at each calibrated point so, 10% at the lowest limit and 90% at the highest limit and 50% at the midpoint.
The Ratiometric output image below shows the ratio metric output of the sensor and how it behaves.
Key rules for Ratiometric pressure sensors to remember are
- Output is 10% to 90% of the supply.
- Low Power.
- If the supply Voltage changes the output value will change.
Ratiometric output summary
Keynote to summarise and remember the output Voltage is proportional to the Supply Voltage. using a pressure sensor example
- Zero pressure – output Voltage 10% of the supply voltage
- Midpoint pressure – output Voltage is 50% of the supply voltage
- Full scale pressure – output Voltage 90% of the supply voltage
Example 1 5V 0-10 bar Ratiometric output pressure sensor
Supply = 5V
Pressure Range = 0-10 Bar
Pressure Span = 10 Bar
Voltage Output = 10% of 5V =0.5V to 90% of 5V = 4.5%
Voltage Output = 0.5V to 4.5V
Voltage Span = ZeroVoltage-FullScaleVoltage 4.5-0.5=4V
Voltage Span = 4.5V – 0.5V = 4V
Therefore
- 0 Bar =0.5V =10% of supply Voltage
- 5 Bar = 2.5V = 50% of supply Voltage
- 10 Bar = 4.5V 90% of supply Voltage
- 0% of sensor input =0.5V =10% of supply Voltage
- 50% of sensor input = 2.5V = 50% of supply Voltage
- 100% of sensor input = 4.5V = 90% of supply Voltage
How to calculate pressure from Ratiometric output Voltage
If the output voltage is 2.5V using the formula above we have.
These equations are simple enough for most Microcontrollers making them a wise chose for embedded systems.
This makes Ratiometric an ideal output type for
- IoT
- Battery powered projects
- Embedded Systems
- Arduino
- Low power systems.
Ratiometric connections
Ratio metric is a voltage output which requires at least 3 connections or wires
Ratiometric Span
The voltage span also depends on the supply voltage, for a typical 5V system the span is 4V. The below diagram illustrate the span relationship to the supply voltage.
The span is calculated by the formula SpanVoltage =ZeroVoltage – FullScaleVoltage
Formula for Voltage output
| Applied Pressure | Voltage Output |
| 0% of Range | Supply Voltage X 0.1 |
| 50% of Range | Supply Voltage X 0.5 |
| 100% of Range | Supply Voltage X 0.9 |
Ratiometric Output to Pressure Equation
Example 2 3V 1-5 bar Ratiometric pressure sensor
Supply = 3V
Pressure Range = 1-5 Bar
Pressure Span = 4 Bar
Voltage Output = 10% of Supply to 90% of Supply
Voltage Output = 0.3V to 2.7V
Voltage Span = ZeroVoltage-FullScaleVoltage
Voltage Span = 2.7V – 0.3V = 2.4V
How to calculate pressure from Ratiometric voltage
If the output voltage is 1.24V using the Ratiometric output to Pressure equation we have
