High accuracy and high stability magnetic displacement sensor in the presence of electromagnetic interferences

A magnetic displacement sensor that comprises:

• a source of a magnetic field that is positioned in a first enclosure that defines a first operative surface;
• a second enclosure that defines a second operative surface which is spaced apart from the first operative surface, wherein the second enclosure includes a first magnetic sensor that is configured to measure the magnetic field density and a second magnetic sensor that is configured to measure the magnetic field density and wherein the first and second magnetic sensors comprise first and second fluxgate sensors that are positioned in tandem and wherein the first and second fluxgate sensors and the source of magnetic field are oriented along an axis;
• and
• means for calculating the separation between the first and second operative surfaces from magnetic field measurements from the first and second magnetic sensors and wherein the first operative surface and the second operative surface define a measurement gap in which a metal containing substrate, which has a first and second side, travels and wherein the first enclosure includes a first distance sensor that determines a first distance from the first operative surface to the first side of the substrate and the second enclosure includes a second distance sensor that determines a second distance from the second operative surface to the second side of the substrate.

A method of measuring the thickness of a web that comprises a metal layer and having a first side and a second side that comprises:

• providing a first distance sensor on the first side of the web;
• determining the position of the first distance sensor relative to the first side of the web with the first distance sensor;
• providing a second distance sensor on the second side of the web;
• determining the position of the second distance sensor relative to the second side of the web with the second distance sensor;
• generating a magnetic field at a fixed location relative to the first distance sensor on the first side of the web;
• positioning first and second magnetic sensors at respective fixed first and second locations to the second distance sensor on the second side of the web wherein the first and second magnetic sensors are aligned coaxially with the magnetic field that is generated;
• measuring the magnetic field density with the first and second magnetic sensors;
• and
• determining the thickness of the web from measurements of the magnetic field density by the first and second magnetic sensors.