Accumeasure Digital Capacitance System D Series Gen 3

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Capacitance Displacement and Gap Measurement Probes

Accumeasure Analog Capacitance System

Basic Principles of Capacitance

Capacitance is defined as the ratio of the change in an electric charge to the corresponding change in its electrical potential (or voltage). Capacitors ; components designed to store electrical charge, consist of conductive parallel plates that are electrically separated by a dielectric material, such as air or an insulating layer.

MTI’s technology is built on the principles of parallel plate capacitor measurement. A probe serves as one of the plates, and a grounded target acts as the other. The capacitance between these two surfaces changes based on the gap or distance between them. This variation in capacitance is converted into an output voltage by an amplifier, which is proportional to the gap distance.

Why Use Capacitance?

One of the main uses of capacitance in industrial applications is the ability to measure without direct contact between the sensor and the target. This means there’s no mechanical loading, wear on probes, or distortion of the target material. Capacitive systems are highly beneficial in industries where non-contact measurements are essential.

Compared to alternatives like laser interferometers, capacitance applications are much more cost-effective while offering comparable, if not superior, stability, precision, and resolution. Capacitive probes also excel in extreme environments, withstanding temperatures as high as 1200°F (650°C) and as low as 4°K (-269.15°C). They are also effective in high magnetic fields (up to 2 Tesla) and can operate in vacuum conditions (10-7 Torr) without issue. Additionally, they can function reliably in humid environments.

Applications of Capacitance in Industry

Now that you have a foundational understanding of capacitance, let’s explore the applications of capacitance in more detail. Whether you’re working with sensors for industrial machinery, measuring small gaps, or assessing the distance between components, it’s essential to understand the specific uses of capacitance in your industry. Additionally, reviewing MTI’s case studies can provide insight into how capacitance measurement systems have been applied in various sectors.

Before implementing capacitance technology into your application, consider the necessary design aspects and requirements. MTI Instruments offers a variety of capacitance measurement systems that cater to different industrial needs, ensuring optimal performance for your specific application.

Uses and Applications

Capacitance is used in a variety of industrial applications. Examples include measuring position and vibration. Whether you need capacitance for standard or advanced uses, you’ll benefit from its accuracy and reliability.

Standard Uses

  • Position Sensing
    • This is probably the most common application for non-contact capacitive sensors.
    • The output of a capacitance sensor is proportional to the distance to the target.
    • Precise positioning is now required in many advanced manufacturing applications.
  • Dynamic Measurements
    • Unlike tripwires, capacitance sensors can provide continuous, real-time measurements.
    • Non-contact sensors are ideal for moving targets because they don’t add mass.
    • Capacitive sensors also have high frequency response for greater precision.
  • Thickness Measurements
    • On-line monitoring is better than periodic, post-production sampling.
    • Thickness measurements may need to be performed at high speeds.
    • Multi-channel measurement supports more than one thickness channel.
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Advanced Uses

  • Position Sensing
    • Supports closed-loop feedback systems for micron and sub-micron precision.
    • Piezo motors support high precision but are less accurate with open-loop linear response.
    • Capacitance eliminates mechanical loading because there’s no physical contact.
  • Dynamic Measurements
    • Real-time data instead of data logging.
    • Frequency and amplitude measurements with component vibrations.
    • Measuring thermal expansion across heating and cooling cycles.
  • Thickness Measurements
    • Capacitance changes when an insulating material is inserted into the gap.
    • This change occurs even if the distance between the probe and target remains constant.
    • The amplifier’s voltage output changes and is proportional to the dielectric’s thickness.

Design Considerations

Before using capacitance with your application, you’ll need to ask and answer a series of questions:
  • What are you trying to measure?
  • What is the level of accuracy that you need?
  • What is the application environment?
  • What are the risks of grounding the target?
  • Do you need continuous, automatic monitoring?

This is just some of what you’ll need to know. That’s why it’s important to choose the right partner, too.

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Industries & Case Studies

Capacitance is used in industries ranging from aircraft maintenance to tire manufacturing. As the following case studies explain, capacitance is also used in consumer electronics and semiconductor manufacturing, wind and solar power, industrial processing, and in the automotive industry.

Consumer Electronics

Electronic manufacturing requires the fast, precise positioning of miniature components. On many assembly lines, process control now demands micron or even sub-micron accuracy. For precision positioning with piezoelectric actuators or voice coil motors, digital capacitance sensor systems combine closed-loop feedback with speed and accuracy.

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Semiconductor Manufacturing

Semiconductor manufacturers are building three-dimensional (3D) integrate circuits (ICs) that feature vertically-stacked silicone wafers and dies. This helps boost device performance, but 3D ICs need coplanar surfaces that make contact with all pins, pads and pillars. To achieve high-resolution position control, capacitance probes are used. The gap measurements are processed with a high-precision digital amplifier.

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Power Generation

The power generators for wind turbines need an optimal gap to ensure peak efficiency. They also need a gap measurement solution that withstands harsh environments and magnetic fields. Corrosion-resistant capacitance probes made of non-magnetic materials are durable and highly-precise. They integrate with digital amplifiers and support the use of custom cables that prevent magnetically-induced currents.

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Solar Technology

The solar industry needs higher-density chips with smaller critical dimensions. Capacitance enables precise measurements, but grounding can damage wafers or interfere with sensing. Pull capacitance systems that measure ungrounded semiconductor wafers remove these risks. They also eliminate inaccuracies by supporting poorly-grounded targets with sub-micron precision.

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Automotive

Brake rotors are now thinner and lighter, but they’re still exposed to conditions that can cause distortion or failure. That’s why the automotive industry needs continuous data collection during testing. Multi-channel measurement systems that withstand high temperatures and provide 24-bit digital readings eliminate errors from analog filtering, linearization, range extension, and the summing of channels.

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Industrial Processing

Oil System Contamination

Water-in-oil contamination can reduce the life of industrial lubricants and increase the cost and frequency of repairs. In-line capacitance probes support a proactive approach to maintenance and, when used with a digital amplifier, can trigger a CPU alarm if the dielectric field reading for an oil flow channel differs from the reading for a sealed oil sample. Monitoring is both continuous and automatic.

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Uses and Benefits of Digital Capacitance Whitepaper

Additional Resources

For additional information about capacitance, visit these resources on the Web.

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