S-series sensor

 

Emfit S-series sensor is a fully shielded, low mass, thin, small area sensor. It typically consists of a sensing element constructed of elastic electret Emfit film and 2 layers of polyester film with screen-printed silver paste electrodes. Several other constructions are possible depending on application-specific needs. Crimped connectors are used for connecting to electrodes. ZIF (zero-insert-force) type connection is also possible.

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Options available are a shielded cable with a heat shrink tube over the joint and 50 microns of acrylic adhesive available on one or both sides of the element.

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S-series sensors are manufactured in sheet laminating. These sensors are always custom-made to a given shape and measurements. Samples available: rectangular 10×20 mm, round 22 mm diameter.

 

 

Uses

Vibration/impact sensing, accelerometers, switches, machine monitoring, acoustic emission detection, contact microphone, acoustic pickup, pyrometer, etc.

 

 

Sensor Operation

Operating in a reciprocal fashion, changes in the thickness of the Emfit sensor generate a corresponding charge and hence, the voltage appears on the electrodes. The transducer behaves like an active capacitor, consequently, the loading of the signal by the input impedance of the measuring device must be considered. Due to the thinness of the films, the associated capacitance can be sufficient to give adequate low-frequency response into standard 1 MΩ loads, but the use of an X10 probe will extend the low-frequency range by a decade.

 

For extremely low force change levels, some buffering may be desirable. For the majority of analysis work, this is unnecessary and the film can feed directly to the instrument. Again, the low mass contributed by the transducer is of major importance to its non-resonate behavior. Frequency response is inherently flat to over 20 kHz with only the R-C roll-off at low frequencies distorting the profile.

 

Though it is responding to thickness change rather than strain, low signal levels may be generated by low frequent flexing, so a distinction must be made between the frequency response of the film for changes in its primary parameter (i.e., thickness) and its relative behavior compared with, say piezoelectric sensors. The sensor has a flat response over a very wide frequency range, with resonant frequency points well above 20 kHz.