Which sensor to choose for SDT: contact, airborne, flexible or parabolic

The sensor decides what the ultrasonic instrument will hear. A contact sensor listens to a structure, an airborne sensor listens to the air. A handful of contact and airborne models cover bearings, valves, leaks, electrical cabinets and tightness. Below is a simple selection scheme and the figures from SDT documentation.

The ParaDish2 parabolic sensor. Photograph by SDT Ultrasound Solutions.

Step one: where does the ultrasound come from

If the source is in a solid part (bearing, gearbox, valve), take a contact sensor. If ultrasound travels through air (a leak, corona discharge, a seal leak), take an airborne sensor. After that the choice depends on distance and mounting place.

Contact sensors

Sensor	What it is	Documented parameters
RS2N	Needle, in three lengths	Resonance 37.2 kHz; lengths 183, 276 and 571 mm; IP54; for LUBExpert, SDT270, LUBEchecker
RS2T	Threaded M6	Resonance 37.0 kHz; tightening torque 2-4 N·m; IP54; for SDT270, SDT200, LUBEchecker
LUBESense1	For bearing lubrication	M6 thread like the RS2T, tuned to the friction signal during greasing; for LUBExpert, SDT270, LUBEchecker
RS Magnetic	Magnetic	Magnet pull 4 kg; weight 35 g; quick mounting on a steel casing

The needle is good for a route: you touch the casing at various points. A threaded sensor is fixed at a permanent point so that readings repeat, which matters for trends and for ultrasound-guided bearing lubrication. For valves see the three-point method.

Airborne sensors

Sensor	Type	Range	Use
FlexID2	Flexible, interchangeable Ø16 and Ø10 mm sensing heads	0-1 m	Hard-to-reach places, leaks at fittings
AIRSense	Airborne with +30 dB preamplifier	0-6 m, up to 15 m with the EDS cone	Leaks, partial discharge, mechanics; 55 degree beam, 8 degrees with EDS
RS2A	For electrical cabinets	Short	Mounted inside an electrical cabinet; weight 135 g
ParaDish2	Parabolic	5-100 m	Distant sources; optical viewfinder, laser pointer

The FlexID2 is 545 mm in its base length, 847 mm with an extension and 1377 mm with a telescopic pole. It fits the SDT340, SDT270, SDT200, ULTRAChecker, HATCHecker and TIGHTChecker.

The EDS2 cone on the instrument's built-in sensor. Photograph by SDT Ultrasound Solutions.

The EDS2 cone screws onto the built-in sensor of the SDT270 and SDT200 or onto the AIRSense. It raises sensitivity by 15 dB (the earlier EDS1 by 10 dB) and makes reception more directional.

Inspecting an electrical cabinet with an SDT airborne sensor. Photograph by SDT Ultrasound Solutions.

Distant sources: ParaDish2

The ParaDish2 is for places where you cannot get close, or not quickly: racks, overhead mains, high equipment. According to SDT documentation its sensitivity is 27 dB above the built-in sensor of the SDT270. The handle folds and the weight is 965 g. The laser pointer is Class 3R, so follow the safety requirements in the datasheet.

Working with the parabolic sensor. Photograph by SDT Ultrasound Solutions.

Distance and signal

Each doubling of distance to the source lowers the ultrasound level by 12 dB. This is why a far search is made with a parabolic sensor, and then you move closer and pin down the point with a flexible one. More: ultrasonic tightness testing.

Compatibility

Not every sensor fits every instrument. The AIRSense works with the SDT340 and ULTRAChecker, the ParaDish2 with the SDT340, SDT270 and SDT200, and the FlexID2 also with the HATCHecker and TIGHTChecker. Check the instrument and sensor pair before ordering. On choosing the instrument itself: guidance on choosing an ultrasonic detector and ultrasonic leak detector comparison.

What to send for selection

The tasks to solve (bearings, valves, leaks, cabinets), distance to the sources, whether there are points for a threaded sensor, and which instrument you already have. Contact KEG TRK to choose a sensor set.

Sources

SDT Ultrasound Solutions sensor documentation: RS2N, RS2T, LUBESense1, AIRSense, EDS2, RS2A, FlexID2, ParaDish2 (DC.PAR2.DAT.01).