Feature: Sensors
Figure 3: A comparison of temperature errors
Figure 4: High-precision, robustness, linearity and temperature tolerance allow an eddyNCDT sensor to track parameters such as the lubrication gap in a combustion engine
Micro-Epsilon’s eddyNCDT3005 line
offers separate compact electronics, allowing different sensor measuring ranges to be packaged with compact “in-cable” M12 electronics. Also, the voltage output is the same as inductive displacement sensors, covering the full 0.5-9.5V, making them fully comparable on a 1:1 basis.
Applications The high cutoff frequency of eddy- current sensors enables metrological detection of distances even in high- speed processes such as machine tools and crankshafts. IP67 protection ensures they can be used in harsh industrial environments where dirt or humidity can affect the measurement. A classic example is monitoring the lubricating gap in a combustion engine (Figure 4) or measuring oil film thickness in hydrostatic bearings (Figure 5).
24 March 2022
www.electronicsworld.co.uk
Figure 5: The compact M12 eddy-current sensors are often used to monitor oil film thickness, e.g., in hydrostatic bearings. The sensors measure the distance from the metallic target “through” the oil film to determine the oil gap
When using eddyNCDT sensors, care
must be taken to ensure they are placed as close as possible to 90˚ relative to the target surface in order to achieve the highest resolution and measurement accuracy. Sometimes, exact right-angle mounting of the sensor to the target is difficult or impossible; see Figure 6. In such cases, the measured values
will deviate marginally from those acquired at a right angle, so the sensor supplier’s graphs are used to factor in the effect of a tilted sensor. For example, with a 4mm sensor and an aluminium target, an inclination of ±4o can be accepted and neglected in most applications. For placement, note that the use of
an air core means the distance from sensor head to target should be 4mm or less.
Figure 6: Sometimes it’s difficult to achieve a right-angle placement for highest performance from an eddy-current sensor. Refer to the manufacturer’s charts to determine how to compensate accordingly
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