Contact vs Non-Contact Measurements

Contact Sensors:

Linear displacement sensors measure the distance between two points or two plane surfaces. Contact gauges imply that the sensor must touch the surfaces. Such sensors could be a LVDT (linear variable differential transformer), string pot gauge (Fig. 1), glass scale gauge, sliding scale, and more. These gauges provide a continuous output of the distance being measured, such as a voltage proportional to the distance, or digital indication in engineering units such as inches or meters. Proximity sensors can be linear but typically are just a switched output indicating when a fixed distance is reached. A simple switch (Fig. 2) with a push rod could be used to indicate when an object being measured has reached a fixed distance.

String Pot Linear distance Sensor

Figure 1 String Pot Linear distance Sensor

Simple Proximity switch

Figure 2 Simple Proximity switch

Non Contact Sensors:

MTI Instruments manufactures multiple non-contact linear displacement sensors. They are either capacitance based, single point laser in one dimension (1D), laser line in two or three dimensions (2D/3D) or fiber optic white light. MTII’s sensors are typically used to measure small precise distances however, some of our 1D and 2 D sensors can measure in inches or hundreds of millimeters.