Capacitance probes are non-contact measurement devices with a capacitance sensor inside a protective shell or housing. They use cables and connectors to integrate with amplifiers and are an important part of capacitance measurement systems. By using capacitance, engineers can measure physical parameters such as vibration, pressure, liquid levels, metal contamination, and seismic activity – just to name a few.
There’s a lot to know about capacitance probes, but five key facts to understand.
- Capacitance probes are highly accurate and very stable.
- They’re better than older devices and competing technologies.
- They require little calibration and support miniaturization and embedding.
- They measure small parameters and can withstand difficult environments.
- MTI Instruments is the innovation leader in capacitance probes and measurement.
The following sections take a closer look.
Capacitance probes are highly accurate and very stable.
Capacitance probes are highly accurate and support 10,000:1 (or better) resolution. Most measurements are non-linear, but there are analog and digital techniques that support linear measurements. The analog technique is called constant current. The digital technique uses a microprocessor and a digital capacitance sensor. These digital measurements are very linear and extremely accurate.
They’re better than older devices and competing technologies.
Early capacitance probes contained amplifier components that caused drift, but today’s digital capacitance probes have achieved stability below 200 parts per million. For applications that require long-term stability and high resolution, capacitance is better than laser technology. It’s also less expensive than other competing technologies. By combing low cost with high accuracy, capacitance has the advantage.
They require little calibration and support miniaturization and embedding.
When a capacitance probe measures a gap, the probe isn’t affected by the target’s temperature or material. This enables calibration-free measurements of absolute distance with stator iron cores and lithium targets. Capacitance probes also support miniaturization through lithography techniques and 3D printing. Even the circuitry can be miniaturized. Consequently, it’s possible to embed these devices.
Embedding requires a clean gap and attention to range and resolution. It’s also important to consider if the target is conductive or can be grounded. When a metallic diaphragm is in front of an embedded capacitance probe, highly accurate deflection measurements are possible. The pressure pushes on the diaphragm and this physical parameter (pressure) becomes a highly stable capacitance reading.
They measure small parameters and can withstand difficult environments.
Capacitance probes can detect very small changes in physical parameters. That’s important since the capacitance of air doesn’t change much with changes in humidity, temperature, or pressure. Yet these probes can also withstand high-temperature, high pressure, and vacuum environments. They can even have a current so low that the capacitance probe is intrinsically safe for explosive environments.
Capacitance probes are also used in difficult environments that simulate outer space. Achieving these conditions requires cryogenic temperatures of around 4° K in an almost absolute vacuum of about 10-8 Torr. MTI Instruments builds capacitive probes to withstand these and other demanding conditions, including challenging atmospheres, extreme climates, and hazardous environments.
MTI Instruments is the innovation leader in capacitance probes and measurement.
MTI Instruments has made advances in digital capacitance technology that the competition still lacks. For example, by using a microprocessor to sample capacitance, MTI has increased stability. We also make smaller capacitance probes than our competitors and support range extension. By reducing the current and using digital techniques and filtering, a probe with a range of 1 mm can achieve 10 mm instead.
MTI Instruments has been providing U.S.-made capacitance sensor systems for over 50 years and continues to set the standard for accuracy and reliability. In addition to standard capacitance probes, we provide push-pull devices and flat polyimide capacitance probes. To learn more, contact us.