How long does ultrasonic rangefinder last

Question

I've built a parking sensor in my garage that uses the HC-SR04 ultrasonic rangefinder and an arduino to measure how far the car is from the back wall.

The one thing that I'm worried about is if the sensor will continue to work for a long time. When it senses an object, it senses distance 10 times per second and once there's a period of inactivity, I scale it down so that it senses distance once per second. So it will be sensing once per second pretty much all the time, which is like 86000 per day, or 31 million times per year. Anyone know if these sensors go bad over time or if they're rated for a certain number of senses?

Thanks for any advice!

Answer 1

First off, sensing the distance once per second may be too slow even for a parking application. Consider that 2 mph is equivalent to over 2.9 feet per second. Almost 3 feet is a large distance in a garage. In any event, I don't think you have to worry about the reliability of the sensor. Quartz watches run continuously for years without any problems. If the watch is analog, that means the parts associated with moving the second hand are operating once per second 24 hours per day or 31 million times per year as you have pointed out. Garage door openers have object sensors to prevent accidents that are also on continuously and last for years.

Answer 2

Just checked on the Sparkfun products (Maxbot)not Sainsmart like your HRC. Their test show their line has a Mean Time Before Failure (MTBF) of 200,000 hours or 22 years. Maxbot makes a big deal of their reliability so the Sainsmart might not be as good but seems like a pretty sturdy kind of component. Maybe Sainsmart has some figures on their products.

Answer 3

Regardless of the manufacturer specified MTBF, all devices will eventually fail. Some will fail much sooner than the MTBF and some will fail later.

The consequence of failure in your case is that you crash your car into the wall of your garage. So you must have a way to deal with failure when it occurs.

One way to deal with failure is to use a redundant system.

1) Build two sensor systems that operate independently.

2) Let the systems share data in some sort of fault tolerant way (isolated serial perhaps).

3) Have each of the two systems indicate a failure if the sensor reading from the other system doesn't match within a certain margin.

If either system fails in any way you will now get a warning from the other one.

You are still not covered in the case where both systems fail at the exact same time, but that case less likely.