difference CAP - SG

What are the differences with closed loop systems between capacitive feedback sensor and strain gauge feedback sensor?


What are the differences between closed loop systems with a capacitive feedback sensor and those with a strain gauge feedback sensor?

Piezo systems with capacitive sensors have better resolution (sensor resolution 1 nm), non-linearity (typ. 0.05%), and repeatability. Capacitive systems are the best choice for applications that require good long time stability. Normally these sensors are arranged in the actuator between the fixed-point and the drive side. Thus, they register the whole mechanical assembly and control the position with high precision.

Strain gauges provide a resolution of up to 35 nm. Their advantages include a small size and large bandwidth of up to 5 kHz. They are a good option for applications with resolutions above 35 nm. A disadvantage is the local configuration of the measurement bridges that do not allow all drift effects to be measured. This reduces their capability to provide high of a long term stability.

Results:

CAP - advantages

  • high measurement accuracy, optimal for long time applications
  • good values regarding non-linearity, repeatability, and resolution
  • cross motion is compensated for e.g. at XY systems

CAP - disadvantages

  • often the actuators have a bigger footprint
  • bandwidth max. of 1 kHz
  • more expensive

DMS - advantages

  • very compact size
  • big bandwidth of up to 5 kHz
  • more cost effective than the CAP

DMS - disadvantages

  • no high long term stability
  • resolution not better than 35 nm
  • cross motion is not compensated for

 

 

 

 


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