Capacitance Sensing vs. Strain Gauge Sensing Application Note

Capacitance probes that are embedded in piezo flexure stages can provide significantly greater accuracy than strain gauges. Although some minor mounting modifications are required, capacitance probes with picoscale positioning provide higher linearity, greater long-term stability, and better direct measurement. Capacitance sensors cost more, however, and are limited by sensing distance. Therefore, strain gauge sensors remain a good choice for applications where cost is a consideration, sensing distances are larger, and high resolution or high accuracy are required.

In a recent application note, MTI Instruments examines the differences between capacitance probes and strain gauges in piezo flexure stages, positioning devices with a high degree of resolution. This app note explains how embedding a capacitive probe in the stage enables precision measurement for applications such as in-situ wafer quality. Typically, the targets for capacitive probes are conductive and grounded; however, capacitance sensors can also be used with glass, sapphire, many plastics, and other non-conductive materials.

MTI’s application note also explains how capacitance sensing and strain gauge sensing work and how these different types of displacement sensors measure either electrical capacitance or electrical resistance, respectively. The advantages and disadvantages of each technology are discussed, and MTI’s app note includes color illustrations. For piezo flexure stages, MTI’s Accumeasure HD Series digital capacitance measurement system can achieve resolutions as low as 20pm with a 10µm range probe. The system’s direct conversion approach eliminates errors associated with traditional analog amplifiers.

Read the app note: Capacitance Probes vs. Strain Gauges in Piezo Flexure Stage