Exploring the PM Sensor

PM working principle

The particulate matter sensor (PM) is an iconic sensor in the National VI system. Its function is to detect the particulate matter content in the exhaust gas. Currently, 70% of practical products are resistive. The pictures below show particulate sensors from Bosch, Stone Ridge, and Continental.

Working principle: Particulate matter will generate a current between two electrodes. As the amount of particulate matter increases, the current value of the particles increases. Therefore, as long as the current value is known, the content of the particulate matter can be deduced. When the particulate matter is saturated, The probe is regenerated, the particulate matter is burned off and the measurement is restarted. Then the time between two regenerations (regeneration interval) becomes the corresponding value of the particulate matter content.

Current detection principle

The figure below is the schematic diagram of the electrode part of the particle sensor. The boost circuit provides a voltage of 45.8V to the high end of the electrode. The CPU detects the voltage value of the low end of the electrode to calculate the current value flowing through the electrode.

PM key technologies

The figure below shows the corresponding relationship between the probe current value and time under a specific environment:

The figure below shows the corresponding relationship between regeneration interval and soot content:

Since the soot content is inferred based on the probe current value and regeneration interval, a large amount of experimental data is essential. It can be seen that the key technology of the particle sensor is:

A large amount of accurate experimental data

Probe manufacturing process (NTK, NGK)

software programming

Probe curve graph

Software status switching and jump diagram

Probe structure

According to the Venturi effect, the greater the flow rate, the smaller the pressure. The flow rate at point A in the figure is greater than point B, so the soot enters from point B and comes out from point A. The soot flows sequentially in the probe.

The probe has three layers. The upper layer is a finger-shaped platinum-based electrode, the middle layer is a platinum heater, and the lower layer is a platinum temperature measurement unit. The pink layer is the aluminum oxide insulation layer, and the yellow layer is the zirconium oxide layer.

Circuit board front

reverse side of circuit board

Interface definition

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