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Reflective Sensor

Hi there. This is my first post on DesignSpark and I am also very new to sensors. I really appreciate any help that someone might be able to offer. 

I am working on a uniflow engine project. I need to control the opening and closing of inlet valve with a sensor. I am currently thinking of using reflective sensors. There will be one reflective point on the crank disc and two sensors to detect it. I need a setup which will open the valve when the output signal is produced by the first sensor and keep it open until the second sensor detects the reflective point and produces it's signal. This will allow for control of the openign time of the valve by moving the sensors relative to each other. I imagine some sort of holding relay? I am unsure whether this exists, however? Or where to start with regards to specifications. If anyone has experience with such a setup or might be able to offer some guidance it would be greatly appreciated.


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June 3, 2019 13:01

Frequently for motor applications an inductive or hall effect (magnetic) sensor is used instead of an optical sensor. These have the advantage of not being affected by ambient light levels, and not being affected by dirt/dust/grease, as long as the dirt/dust doesn't contain metal filings. Inductive sensors are most commonly module-level products, while the magnetic (hall effect) sensors like the Honeywell SS40A (RS # 822-3778) are frequently chip-level products that can interface directly to a processor. When choosing hall effect sensors, pay attention to the response frequency. Some units sample less frequently in order to minimize power usage, and might not sample fast enough for the speeds you might be wanting.
I'd use a small processor board like an Arduino to handle logically combining output from multiple sensors. It will give you more flexibility than a relay would, allowing you to implement variable delay implement variable output power, etc.

June 1, 2019 17:25

You should also consider whether the relay you propose would respond fast enough. They have an actuation and release time and a maximum operating frequency as well as a contact life (number of operations). If you continue with the proposed design I suggest an electronic interface to the sensors and driving the valve. This could be discrete or a uC design, the latter will give you some further optimising options such as varying the delay between the valve and the speed or during acceleration (vacuum advance in the good old combustion engine designs), but these may have no use on a uniflow engine, so you can decide the best approach.

0 Votes

May 30, 2019 15:42

I'm a little unsure about how you would use a photoelectric sensor with a reflector, if that is what you mean by reflective sensor, to control the inlet valve which I presume controls the speed and your looking to create a closed loop system

Wouldn't you be better using a small servo on the inlet valve e.g. (174-3258) to control the position and if you have a small motor acting as a generator on the flywheel then you could use that as velocity (voltage) feedback to determine the delta position the valve needs to be in and thus control the speed of the engine with a potentiometer in a closed loop system.

I've done a sketch of a potential system to help explain, see attached