A key supplier to the aerospace industry who manufactures many types of solenoid door latches was faced with the requirement to measure the motion of the lock plunger.

Since the solenoid latch needs to complete the locking or unlocking cycle in as quickly as 13 milliseconds, it was critical to accurately track the fast motion of the plunger with a measurement system having a frequency response in excess of 100kHz. Because of the limited access to the interior of the cockpit door plunger/solenoid assembly, a compact, rugged and fast response sensor would be needed.

After a thorough analysis by MTI Instruments’ application engineers, the MTI-2100 Fotonic sensor was selected to make this measurement. The MTI-2100 transmits a beam of light through a fiber optic bundle onto the target surface and the amplitude of the reflected light returning back to the probe generates a very precise curve of volts vs. distance.
With a response time of up to 200 kHz, there is minimal phase delay in measuring the solenoid motion and the probe is also immune to any electromagnetic interference (EMI) present in the vicinity of the latch assembly.

The MTI-2100 Fotonic sensor was tested at the suppliers’ facility and was able to precisely capture the solenoid plunger motion. An unexpected discovery while testing the system was that it was also able to see previously unknown plunger oscillations due to the solenoid striking the solenoid back stop. Since these oscillations can severely affect the solenoid performance and limit response time, careful analysis of this data resulted in an improved product design with an increase in speed and performance. The specific probe module selected to use with the MTI-2100 was the MTI-2125H with a wide measurement range of 4.5-mm. (0.175”) at a standoff distance of 7.6-mm, (0.300”).

Since these oscillations can severely affect the solenoid performance and limit response time, careful analysis of this data resulted for aerospace manufacturer to improve their product design with an increase in speed and performance.