 Dielectric
sensors from Micromet Instruments are available in a variety of configurations
for a wide range of applications. Sensors have been designed to work
in autoclaves, molding presses, ovens, fluids, and other environments.
Sensors are available with upper operating temperatures of 707F/400C
and pressures of over 5000 psi. Some sensors are available with a thermocouple
as an integral part of the sensor. The sensors can be described in
two general categories - implantable (disposable) and reusable (Tool
Mount). Within these two categories sensors can be divided again -
surface (or fringe) measurement sensors and bulk (or through part),
measurement sensors.
Dielectric sensors require intimate contact with the material under test.
Sensors can be located on the surface or within the material. The sensors
are operated by applying a voltage across the electrodes at a chosen
frequency(s) and measuring the resultant change in amplitude and phase.
From these properties the Permittivity (E') and Loss Factor (E")
are calculated. Ion Viscosity, or electrical resistivity, is extracted
from the Loss Factor and is directly related to the mobility of ions
in the material. For most polymers, Ion Viscosity follows closely the
changes in mechanical viscosity and cure state.
Sensor Types
Surface, or fringe, measurement sensors are comprised
of two planar interdigitated comb electrodes on an inert substrate
and are available in a variety of electrode spacing configurations.
The electrode line width and the spacing between the electrodes determines
approximately how far into the material the fringe field will measure.
For example, the MS-25 sensor which has line widths and electrode spacing
of 25 microns will measure approximately 25 microns into the material. |
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Bulk, or through part, measurement sensors
consist of one electrode and typically use the mold wall as the other
electrode. Bulk measurements are also made with parallel plate sensors
which consist of two electrodes.
Sensors can be located over 100 feet from the instrument or interface box,
depending on the instrument used. For autoclave applications an autoclave
feedthrough assembly is available. Tool Mount Sensors are factory hardened
for in mold production applications. Different lead lengths, cable configurations
and temperature ranges are available for most sensors.
Thermocouples (J and K type), pressure sensors, and other analog sensors
may be used with Micromet's line of instrumentation.
Tool Mount Sensors
Implantable Dielectric Sensors
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