Auto Zero

In most applications, the pressure sensor is considered the primary reference and is perhaps the only pressure measurement in the entire system. Therefore, one of the most important factors to consider when using any re-calibration method is that there must be a known Reference Pressure condition that can be applied to the sensor.

While this known and stable Reference Pressure condition is being applied to the sensor, the end user can measure the output of the sensor and detect if the Offset has changed (Offset Shift and Offset Drift), determine how much it has changed and correct for it digitally in the system.

Auto-Zero is a compensation technique based on sampling output at a known reference condition, within the compensated temperature and pressure range of the product. Typically, a zero pressure reference such as atmospheric pressure (or equal pressure on both pressure ports for a differential product) is employed to allow the external correction of Offset error.

Dual ported sensors do not necessarily require that the system pressure is zero to be able to implement an Auto-Zero but rather that both ports are at exactly the same pressure. In addition to venting both ports to the atmosphere, this can also be achieved by using a valve to shunt the pressure between the ports so that both ports see the same “system” pressure. This creates the same pressure on both sides of the pressure sensor die which results in the same condition as having both ports at zero pressure.

In many applications, a zero condition doesn’t naturally occur, therefore a valve may need to be used to connect/disconnect pressure from the sensor’s port(s) to create a known Reference Pressure condition.