Pressure error can be measured by which of the following ?

The correct answer is: A. Differential bellows and straingauge.

A differential bellows is a device that measures pressure by detecting the difference in the pressure on two sides of a bellows. A strain gauge is a device that measures strain, which is the deformation of a material under stress. When a strain gauge is attached to a bellows, it can measure the strain in the bellows, which is proportional to the pressure difference across the bellows.

The other options are incorrect because they do not measure pressure error.

• Selsyn is a device that transmits angular position or rotational motion from one location to another. It does not measure pressure.
• Strain gauge is a device that measures strain, which is the deformation of a material under stress. It does not measure pressure error.
• Strain gauge and potentiometer are two devices that can be used to measure strain. However, they cannot be used to measure pressure error.