Hi Yenhaeng,
MPX2200AP means that you are using absolute type and not gauge (GP) as you wrote earlier.
When using MPX2200AP, it is expected to have about 20mV on the output as the ambient local pressure is around 100kPa absolute. Then considering the sensitivity of 0.2mV/kPa you will get 20mV.
Only for D/DP/GP variants the output voltage should be between -1mV and +1mV when no pressure is applied.
Best regards,
Tomas
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