MPVZ4006 Output resolution

[johnteller]

Hi there,

I have purchased a MPVZ4006 pressure IC. My question is what is the actual output resolution of the IC is in mV, or in other words what is the resolution of the pressure (smallest unit that can be read) in Pa.

I understand that using a 10 bit ADC I can theoretically get a resolution of 6kPa/(2^10bit)=5.86 Pa. This corresponds to an IC output voltage resolution of 4.48mV approx.

So with a 12 bit ADC I would get a theoretical resolution of 1.46 Pa, corresponding to IC output voltage resolution of 1.12mV.

But will the IC actually be able to display such small increments?

So I guess my question is whether the IC itself has a minimum resolution and if so what is it?

Thanks

JT

[Joshevelle · Accepted solution]

Hello John,

First of all, thanks for using our community.

The MPVZ4006 is an analog device; theoretically speaking there are infinite values between one "step" and another. Hence, as you mentioned, the resolution depends mostly in the ADC that you're using.

The MPVZ4006 has a pressure range from 0 to 6kPa, let's say you need a resolution of 0.01kPa, then you'd need ~600 ADC counts (6kPa/0.01kPa), 600 counts can be obtained with a 10 bit ADC (2^10=1024). Hence any 10bits ADC would do the job.

Please notice that in such "sensitive" systems, small noise levels could be a problem. The MPVZ4006 has a full scale range of 4.6v (0.2 to 4.8v), hence in the last example you'd measure output voltage changes of ~4.5mV/count (4.6v/1024counts).

The smaller the resolution, the smaller the voltage per count and the more ADC bits.

The following application note might be useful in your application:

AN1646: Noise Considerations for Integrated Pressure Sensors

        http://www.freescale.com/files/sensors/doc/app_note/AN1646.pdf

However, if you’re interested in high sensitivity, I would recommend you to consider the accuracy of the device. The MPVZ4006 has an accuracy of +-5%, which equals to 0.3kPa.

In order for you to increase the accuracy to around +-2.46%, you’d need to implement “Autozero”, a software technique that basically reads the offset of the pressure sensor and compensates the sensor’s measurements to meet your requirements, regardless of the offset level of each specific sensor.

Auto-Zero:

http://cache.freescale.com/files/sensors/doc/app_note/AN1636.pdf

I hope you will find this information useful, please let us know if you need further support.

Regards,

Josh

[johnteller]

Thanks for the clarification, I will look at those documents.