PUSH/PULL PROBES Capacitive Position Sensor

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Key features

• Eliminates inaccuracies created by poorly grounded targets
• Can measure highly resistive targets
• Cancels common mode electrical noise

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About Capacitance Probes - Push/Pull Probe sensors

Capacitance Technology

Standard capacitive sensors require the target to be electrically grounded. Current flows from the probe face to the target and back to the amplifier to complete the circuit. The capacitance between probe and target is proportional to the distance and converted to a 0 - 10V output from the amplifier. The measurement of electrically grounded targets can be, however, affected by changes in the electrical conductivity or ground path of the target.

Unique Push/Pull Technology

To eliminate the effects of these variations, Althen developed a unique version of the Accumeasure sensor called the push-pull. In this design each probe consists of two capacitance sensors, built into one probe body. Each sensor is driven at the same voltage, however, there is a 180 degree phase shift between signals. This shift allows the current path to travel across the target surface rather than through the target to ground, eliminating any inaccuracies created by poorly grounded targets. Additionally, highly resistive targets can be measured with this technology allowing capacitance sensors to be used on semi-insulating and semi-conducting targets.

Additionally, the push/pull amplifier design cancels common mode electrical noise that may be induced in this target. Common mode noise may be encountered in magnetic bearing surfaces, semiconductor wafers, brake rotors and air bearing floating surfaces.

Applications for Push/Pull probes

• Semiconductor thickness
• Sheet metal thickness
• Photovoltaic wafer thickness
• Automotive brake rotor run-out
• Thickness variation
• Leveling or flatness measurements

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