What is Ratiometric Output?

In many pressure sensors, the electrical output signal depends on the supply voltage. This is a common feature for unamplified sensors and sensors that do not have built-in power-supply regulation.

The span output of an unamplified device is essentially ratiometric (or proportional) to the excitation voltage applied. This effect is common on Wheatstone bridge sensor types where the output is normally specified as something like 2mV/V, which means that the output from the sensor is 2mV for full-scale pressure/load/force with an excitation voltage (power supply) of 1V applied.

If you then supply the same sensor with a 10V excitation voltage, the output signal would be 20mV for full-scale pressure (10 x 2mV).

Is the sensor ratiometric?

Other pressure sensors may exhibit the same effect, but it is not always as simple to identify as in the above example. The words to look out for are “this sensor is ratiometric”. To ensure correct usage contact the supplier, or if possible refer to the complete specification/documentation of the sensor.

For sensors with built-in power supply stabilisers (normally combined with amplified output), a variation of supply will have no effect on the output, as long as it is within the specification.

In this case the excitation voltage is specified as a minimum to maximum voltage range such as 8 to 20V.

Read more: Index to all of our Technical Notes on Pressure

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