NTM88 pressure values coming wrong

[ankit2631]

I am using NTM88 for Tire Pressure Monitoring application. i am converting the Vcodes received from the sensor to KPa using the transfer function in datasheet (Transfer function: P kPa = (0.824 kPa / LSB × PCODE) + 88.353 kPa) and converted to Psi by diving the result of above transfer function with 6.895 as directed by online converters. But when I installed it inside the tire and filled the air in it the analog pressure gauge value is showing pressure as 40Psi whereas NTM88 is showing the value as 52.489Psi.

so in order to achieve the accuracy i removed the offset of 88.353 stated in transfer function. now my values are coming properly and matches with the values shown by the pressure gauge. why is it behaving like this? I am doing something wrong.?

[QuangLaoCa]

Hello, i have the same problem with ankit2631.

I use NTM88J135S and apply “P kPa = (0.824 kPa / LSB × PCODE) + 88.353 kPa” formula.
In my car actual pressure is 33PSI but the value feedback from ntm88 alway 45PSI.
How i can refer?

[TomasVaverka]

Hi Ankit,

NTM88 belongs to absolute pressure sensors, the reference mentioned by you is a gauge pressure sensor.

Absolute pressure = Gauge pressure + Atmospheric pressure (about 100kPa)

88.353kPa you removed is close to the value of atmospheric pressure. However, it is not recommended because an atmospheric pressure is not a fixed value and changes with the variation of weather and altitude. An absolute pressure sensor can work as a reference of a gauge pressure sensor, but a gauge pressure sensor cannot work as a reference of an absolute pressure sensor.

BTW, NTM88 family has multiple measurement ranges with different transfer functions.

The transfer function you mentioned is “P kPa = (0.824 kPa / LSB × PCODE) + 88.353 kPa” for the measurement range from 90kPa to 930kPa. Please check if correct PN is applied.

Best regards,

Tomas

[ankit2631]

Hi Tomas,

Thanks for the explaination, but my concern now is how can i use this for my tire pressure monitoring application.