Distributed Impedance Sensor Technology, or DIST, is LRT Sensor’s patented technology that is used to design and manufacture our standard series of non-contact linear sensors. This know-how is also applicable to rotary, gap sensing and liquid level applications on a custom basis.
The Distributed Impedance Sensor Technology sensor, in a manner similar to inductive sensors, follows the fundamental laws of physics concerning changing electromagnetic fields. In a perfect vacuum an electromagnetic wave will travel forever at the speed of light in a straight line with no energy loss. However, if the electromagnetic wave encounters any material, the energy and the direction of the electromagnetic wave will be changed. The amount of the change can, in theory, be calculated by a set of equations called Maxwell’s equations which is beyond the scope of this paper. A position sensor determines the change in the wave and from that we can calculate the presence and position of material in the wave’s path. So, if something moves into the path of the electromagnetic wave, the wave will be distorted in a predictable manner. If we measure this distortion it is possible to determine the motion and or position of the material in the wave’s path, i.e. a position sensor.
Two popular sensors used in applications similar to that of the Distributed Impedance Sensor Technology Sensor are LVDT’s and magnetostrictive sensors.
Distributed Impedance Sensor Technology Linear Sensor
The DIST sensor consists of a double coil wound on a round non- conductive rod (usually fiberglass). The wire is wound as a helix with a large pitch. Upon reaching the end of the shaft, the pitch is reversed and a returning helix is laid over the first coil. This is shown in Figure 1 below where the enlarged view shows the position of both coils. In the electronics section, a simple circuit consisting of a single transistor is connected to the ends of the coil, producing a resonant circuit that oscillates in the 2-4 Mhz region. The result is two coils in series with one having current flowing clockwise and the other counterclockwise. The magnetic fields of these two coils are parallel to the sensor, point in opposite directions and cancel each other by the “right hand rule”. At the same time the electric fields from these circulating currents are perpendicular to the rod and again, by the “right hand rule”, they are additive. The resulting electromagnetic field outside the coil is then mostly electric with a minimal magnetic component.
To read about the technology comparison of the DIST non-contact position sensor with LVDT’s and Magnetostrictive Sensors, download our white paper.