Capacitive TechNote LT03-0024
Copyright © 2007 Lion Precision. www.lionprecision.com
Summary
Specifications and recommendations for capacitive probe cables to maximize performance and durability.
Capacitive Probe Cabling Considerations
Mechanical
High-Temperature FEP Cable
Operating Temperature
-250°C to 200°C (cable only)
Capacitive probes are only rated for a temperature range of 4°C to 50°C. The cable has a much wider temperature range.
Cable Length/Extensions
Cable length effects calibration because drivers transmit a high-frequency signal to the probe through the cable. Sensors should be calibrated with the same cables and cable lengths that will be used in operation. If extensions are going to be used, the system must be calibrated with the extensions.
Standard cable length is 2 meters and is measured according the diagram below.
Custom cable lengths can be ordered.
Cable Movement During Measurement
Error Noise Generation
Moving the cable can generate noise caused by the “triboelectric” effect. This effect creates small voltage spikes in the cable due to static charges created when the conductors and insulation rub together. This noise is then amplified by the driver electronics and appears in the output signal of the sensor as an error component.
This effect is part of the physics of cabling and is not a function of the driver or probe design. Cable used in Lion Precision probes is specially designed to minimize triboelectric noise.
Generally, this effect is dependent on acceleration. Quick movements of the cable generate more noise than gradual movements of the cable. Impacts on the cable are worst case.
Flexibility (Minimum Bend Radius)
Bend radius is measured on the “inside” of the bend.
The allowable bend radius depends on the application.
Select an application below to find the minimum bend radius. Note the measurement of the bend radius on the right.
Dynamic Applications (Repeated Bending):
At cable/probe junction: None. Secure cable to prevent repeated motion at the junction of the cable and probe.
Along cable length: 50mm (2″)
Static Applications (Bent occasionally during installation):
At cable/probe junction: 25mm (1″)
Along cable length: 7.5mm (0.3″)
Extreme Applications ( Bent only once for extremely tight installations):
At cable/probe junction: 13mm (0.5″)
Along cable length: 2.5mm (0.1″)