AD7150 /AD7156

Main difference is in the supply and the ADC conversion time.

AD7156 supply voltage is lower at 1.8V - 3.6V with higher ADC conversion time of 20ms.

AD7150 supply voltage is 2.7V - 3.6V with faster conversion time of 10ms.

Main difference is in the supply and the ADC conversion time.

AD7156 supply voltage is lower at 1.8V - 3.6V with higher ADC conversion time of 20ms.

AD7150 supply voltage is 2.7V - 3.6V with faster conversion time of 10ms.

Please refer to the article ADI Capacitance-to-Digital Converter Technology in Healthcare Applications | Analog Devices

Shielding is needed to ensure that the capacitance measurement is free from surrounding disturbances whether internal or external. 

Regarding EMC protection, please refer to the Apps note AN-1011 EMC Protection of the AD7150 Application Note (Rev. 0) Data Sheet (analog.com)

Thank you for your quick replies. Do you have any knowledge about how the shielding is solved with FPC/FFC cables like the ones used on membrane panels? I assume, apart from the shield around the cable,  a shield conductor is needed between every Cin and Exc connection? If both Cin and Exc connections are close together but within one shield, they could not pick up disturbances? Is there any requirement about minimum distance from each other?

We have no experience with shielding on the FPC/FFC cables. The signals each on CIN and EXC are to be shielded in any case whether separately or with common as mentioned in the article above.

There is no minimum distance requirement. 

Are there any limitations about sensor size, apart from capacitance?

As we want to use quite large sensors, we need to be careful not to exceed the maximum 4pF capacitance. If we for some reason get/want higher sensor capacitance (due to size), is there any way we could lower this total capacitance to get below 4pF? For instance a series capacitor could be used, how would this affect sensibility?

There is no limit on the sensor size. 

You can use a basic capacitance equation to determine the size and the plate distance while targeting the sensor capacitance.

You can also increase the range of the sensor capacitance by referring to the circuit note https://www.analog.com/media/en/technical-documentation/application-notes/AN-1585.pdf