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MPX5999D 一些应用问题

When this sensor is used in an electronic pressure controller, the working principle of the electronic pressure controller is to change the flow rate by adjusting the opening of the proportional valve, thereby changing the pressure. The pressure measurement uses your pressure sensor. By comparing the sensor reading with the set value, the opening of the proportional valve is adjusted so that the pressure value set by the host computer matches the actual pressure value. The pressure value to be controlled is the differential pressure value output by the sensor. Throughout the process, the set value from the host computer remains unchanged; the set value is the differential pressure value, and the controlled value is also the differential pressure value. When P2 = 100 kPa, the electronic pressure controller works normally. When P2 decreases from 100 kPa to 80 kPa, the output flow rate of the electronic pressure controller approaches zero, far lower than the set value. Is this a problem caused by the sensor? What are the possible solutions?

Re: MPX5999D 一些应用问题

Hi Yuwei.

Thank you for the explanation of your control system. Based on your description, this is not caused by a malfunction of the MPX5999D. The sensor is operating correctly.

The drop in flow rate is a natural pneumatic reaction of the control loop: when reference pressure P2 drops from 100 kPa to 80 kPa, the controller must automatically lower the absolute pressure P1 to maintain the exact same differential setpoint. This drop in absolute pressure reduces gas density and driving force, which naturally chokes the flow rate through the proportional valve down to near zero.

To resolve this, I think you can either vent the P2 port to a stable atmospheric reference to decouple it from the pressure shifts or dynamically increase the differential setpoint in your software to compensate for the lost gas density when P2 decreases.

BRs, Tomas

PS: STMicroelectronics has already finalized its acquisition of NXP's MEMS sensor business. All production, support and documentation for these sensors have fully transferred to ST.