Abstract: A probe for the measurement of the level of conductive materials within a conductive vessel is disclosed which is particularly suitable for the measurement of the level of conductive granular materials such as coal or other minerals or plastics or vegetable matter which are conductive. In a preferred embodiment the probe comprises a conductive steel core covered with a layer of insulating plastic and covered further with a layer of a semi-conductive material which preferably comprises a plastic which has been partially filled with a conductive material such as carbon black. Other embodiments wherein the probe may comprise a conductive plate covered by insulation further covered by a similar semi-conductive layer are also disclosed. Reference is made to prior art disclosures of circuitry and theory which enable the use of the probe of the invention.

Abstract: A probe for the measurement of the level of conductive materials within a conductive vessel is disclosed which is particularly suitable for the measurement of the level of conductive granular materials such as coal or other minerals or plastics or vegetable matter which are conductive. In a preferred embodiment the probe comprises a conductive steel core covered with a layer of insulating plastic and covered further with a layer of a semi-conductive material which preferably comprises a plastic which has been partially filled with a conductive material such as carbon black. Other embodiments wherein the probe may comprise a conductive plate covered by insulation further covered by a similar semi-conductive layer are also disclosed. Reference is made to prior art disclosures of circuitry and theory which enable the use of the probe of the invention.

Abstract: A probe for the measurement of the level of conductive materials within a conductive vessel is disclosed which is particularly suitable for the measurement of the level of conductive granular materials such as coal or other minerals or plastics or vegetable matter which are conductive. In a preferred embodiment the probe comprises a conductive steel core covered with a layer of insulating plastic and covered further with a layer of a semi-conductive material which preferably comprises a plastic which has been partially filled with a conductive material such as carbon black. Other embodiments wherein the probe may comprise a conductive plate covered by insulation further covered by a similar semi-conductive layer are also disclosed. Reference is made to prior art disclosures of circuitry and theory which enable the use of the probe of the invention.

Abstract: A transmitting system including an admittance sensing probe having sensing elements adapted to sense both the composition and the level of materials. The probe is coupled to admittance responsive networks forming part of a common oscillator which generate admittance signals representing the level and composition of the material. A remotely located power supply provides current to the transmitters through two pairs of lines, and the output currents of the transmitters represent the level and composition of the materials.

Abstract: A two-wire transmitter includes an admittance sensing probe adapted to sense the conditions and corresponding admittance of materials. The probe is coupled into an admittance responsive network which generates an admittance signal representing the condition of materials. The output current from the transmitter is varied in response to the admittance signal. In one embodiment of the invention, the admittance responsive network comprises a variable frequency oscillator whose frequency varies with the admittance of the materials. In another embodiment, the admittance responsive network comprises a ramp generator with a frequency which varies with the admittance of the materials. In another embodiment, the admittance responsive network comprises a bridge whose balance changes in response to the admittance of the materials.

Abstract: An intrinsically safe system for monitoring the condition of materials includes a low power, stable frequency RF oscillator of the class C type comprising a resonant circuit which is coupled to a bridge network including the admittance of materials between a probe electrode and a grounded support member juxtaposed to the materials. The output of the network generates an AC error signal which is applied to a phase sensitive detector including a chopper and a low power chopper drive for generating a DC signal representing the magnitude of the AC signal at a predetermined phase angle. The bridge network which may be linearly calibrated is isolated from the oscillator and the output error signal circuitry so as to allow the oscillator and the output error signal circuitry to float with respect to the grounded support member and the power supply associated therewith.