Object(s) invisible to Pololu Digital Distance Sensors

Robotics and electronics discussion Electronics
1

I’m trying to use a #4052 Polulu sensor to monitor a fan. Even when the fan is stationary the sensor can’t see the fan blades. Are there materials that the sensor just can’t see? The fan blades have quite a steep pitch as well but I have tried to compensate for that.

2

Depending on their IR reflectivity of the material, it might be difficult for IR sensors like our Digital Distance Sensors to detect reliably. For example, black plastics can sometimes be hard to detect, especially at more extreme angles. Have you confirmed that the sensor is working as expected separately from the fan (i.e. the output goes low when you put your hand in front of it and is high otherwise)? Could you post some pictures of your setup that show all of your connections, as well as the sensor and fan orientation?

Brandon

3

Thanks Brandon, yes, the sensor works when I fan my fingers at it and the fan blades do appear to be black or nearly-black plastic with a matt finish. It is a little difficult to photograph the setup since the fan is in a ducted enclosure behind quite a dense grille and I’m not keen on opening it up. I have achieved partial success by altering the setup: My starting point was a 10 cm #4052 sensor positioned about 5 cm away from the blades which should have put the ‘sweet spot’ some way into the blades. I substituted a 25 cm #4066 sensor, still 5 cm away which is now seeing it. The signal is a bit ragged but given that I am getting a weak signal rather than none at all I suspect that some experimentation can clean it up. Angling the sensor with respect to the blades for instance. FYI the application is that I’m monitoring the behaviour of my air-source heat pump system which I need to do ‘hands-off’ so as not to upset the manufacturer or installer hence external sensors. Regards John

4

Consider spraying white or silver paint at a spot on a fan blade to increase reflectivity.

5

Thanks, that would be Plan ‘B’ - silver paint or retroreflective tape which I have somewhere. Silver better than white perhaps since what is white in visible light might not be so reflective in IR?