Sensors & transducers
The compact M12 eddy current sensors are often used for
monitoring 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.
Temperature cycling of the sensor and then storing its response to enable temperature compensation in the field are key steps during manufacture and production. These are what give Micro-Epsilon sensors high stability over wide temperatures ranges, over the full scale of operation.
eddy current sensors eliminate packaging and housing limitations
Both proximity and inductive displacement sensors can be housed in solid metal (food compatible, high resistance grades). Eddy current sensors’ operating principle means they must use a non-metallic cap. Despite this, Micro-Epsilon eddy current sensors are still certified to IP67. In addition, the packaging of eddy current sensors has been advancing rapidly, with the electronics being integrated into the device. Most significantly, the eddyNCDT
3001 product line signifies a new class of eddy current sensors that come in an M12 housing with both the integrated controller and signal- conditioning unit. This makes them much more amenable to standard mechanical formats and requirements, as well as making them a more attractive replacement option for inductive displacement sensors. The new eddyNCDT3005 from Micro- Epsilon has separate compact electronics which enables many different sensor measuring ranges to be packaged with compact “in- cable” M12 electronics. Other characteristics include the ability to withstand up to 300 bar of ambient pressure. Also, the voltage output is the same as inductive displacement sensors, covering the full 0.5 to 9.5V, making them fully comparable on a 1:1 basis.
applications and usage
The high cut-off frequency of eddy current sensors enables metrological detection of distance values even in high speed processes such as machine tools and crankshafts. IP67 protection ensures they can also be used in harsh industrial environments where dirt or humidity will not influence the measurement result. A classic example is monitoring the lubricating gap in a combustion engine. Custom sensor designs for specific
needs are possible, including specific target object calibration, mounting options, individual cable lengths and modified measuring ranges, as well as pressure tolerance to 2,000 bar. 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 an exact right angle mounting of the sensor to the target is difficult or impossible. In such cases, the measured values
will deviate marginally from those acquired at a right angle, so use the sensor supplier’s graphs to factor in the effect of a tilted sensor. For example, with a 4mm sensor and an aluminium target, an inclination of ± four degrees can be accepted and neglected in most applications. For placement, note that the use of an air core means that the distance from sensor head to target should be 4 mm or less.
Micro-Epsilon
www.micro-epsilon.co.uk
Benefits of eddy current Non-contact measurement of displacement, distance
and position on ferro- and non-ferromagnetic materials High resolution and temperature stability
Temperature range -40°C to 200°C and higher Robust and reliable sensors IP67 Resistant to oil, dust and dirt
Instrumentation Monthly February 2022 39
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