ping))) behavior above the limit of 3m

Panos0

Hi!
I would like to know which is the exact output that ultrasonic sensor ping))) gives in echo pin when the distance of the target is longer than 3 meters,which is the high limit according to datasheets,(f.e.4,5,10 OR 1000 meters!)???

And how can i find such detailed information?(data sheets don't help)

Mike Green

Actually the datasheet is the proper reference for that information. tIn-Max defines the maximum time that the Ping will respond to an echo, approximately 18.5ms as shown on page 2. That's distance there plus distance for the echo to return. The actual distance depends on the speed of sound (and the temperature) as shown on page 3. You'll have to compute the maximum distance given the air temperature.

Panos0

Mike Green wrote: »

Actually the datasheet is the proper reference for that information. tIn-Max defines the maximum time that the Ping will respond to an echo, approximately 18.5ms as shown on page 2. That's distance there plus distance for the echo to return. The actual distance depends on the speed of sound (and the temperature) as shown on page 3. You'll have to compute the maximum distance given the air temperature.

Thank you for the answer! I'm a litle new so sorry for these simple questions but it is very important for i'm doing my thesis these days!!

So if i understand well if the distance of the target is so big that the ultrasonic sound didn't come back, then the sensor will give to the echo pin a TTL pulse with 18.5ms duration. (which means that the distance is 18.5ms*(343/2)=3.17m)

343=sound speed

Thank you again!

Mike Green

You have the basic idea. If the distance is such that the sound pulse never returns or even if it returns, but later than 18.5ms, the Ping will ignore it and report an 18.5ms echo time.

Panos0

Mike Green wrote: »

You have the basic idea. If the distance is such that the sound pulse never returns or even if it returns, but later than 18.5ms, the Ping will ignore it and report an 18.5ms echo time.

Thank you again for your help Mike Green very much!:D

Panos0

I would like to do another one question!
If the distance is less than 2cm then the echo will be 115us and will not go down to 115us OR the ultrasonic sound will lost to the side (so will not come back) so the echo will be 18.5ms (the maximum limit)??

Mike Green

I don't know for certain, but I believe the holdoff time effectively disables the PING receiver until 115us from the ultrasound pulse, so the PING will not detect the echo from an object less than 2cm. At that distance there may be other indirect echos that might trigger the PING unless the object is very small. You'll have to experiment. There are too many variables to say for certain.

RinksCustoms

Funny thing about air currents between the target and the ping, this may not affect ultrasonics at close to medium range, but as range increases, air currents within the measuring range raise the air pressure just slightly -density change. Some of the variables for the transport of ultrasonic acoustic waves in a fluid is whats called density altitude (the calculated current air density based on altitude, humidity and air temp -pilots use this frequently as a check for lift or how well the relative conditions will be able to produce lift on an airplanes wing). The density altitude will have a bigger affect on accuracy with longer measurements unless it is taken into consideration. I also observed an interesting effect on distant higher pitched sounds between winter and summer weather. In winter, with winds rel calm and a clear line of sight to the high freq -like a whine from a jet engine idling- (audible) emission source and say 1/8-1/4 mile distance and not snowing, detail was undistorted and crystal clear. When it would snow it sounded as if there was a high pass filter on the sound where the lower frequencies were still crisp but had a high frequency roll-off effect. The more heavily it snowed, the quieter everything got.
As far as summer goes, same distance to target as above, but noticeable inconsistencies with how well the air transmitted the jet engine whine -as if someone were varying a tonal control at the source. From my observations, it is clear to me that trying to measure great distances with ultrasonic waves depends largely on the current properties of the air between your ultrasonic sensor and the target object & the targets surface acoustical properties -smooth, hard surfaces reflect a cleaner, sharper acoustic image than a coarse &/or soft surface.
The hotter the air mass, the less density -has a natural tendency to roll-off higher frequencies vs distance- also precip or humidity compounds this effect further by acting as an effective acoustic damper. In my opinion, ultrasonic is not a viable solution for med-long range measurements due to too many variables having wide spread effect on the measurement.

Panos0

thanks for the help!
Of course the best is to experiment with this although i' m making a simple parking sonar and I hope not to have problems with the air - temperature characteristics!!

RinksCustoms

one big problem is going to be keeping the ping sensor dry and keeping the moisture from getting all over the transducers. Most of the automotive style transducers are two wire. Auto makers usually employ four transducers per bumper, like chevy, nissan, toyota (lexus), and ford. They are probably able to take a bit more power and thus have better range.. these sensors are also water resistant/proof. As far as parking radar goes, the effects i spoke of before will be almost negligable for your intended purpose. I was merely pointing out sone observations made of the physics and variables behind what would affect longer range ultrasonic rangefinding. There is one frame straightening/measuring system used by autobody shops that actually uses ultrasonic sensors at various anchor points under a cars chassis and send pulses to a central metal beam loaded with the ultrasonic microphone sensors. Its called SHARK, this system is cheaper than precision variable pot/angle systems like the car-o-liner system, but it has a few drawbacks. It cant measure upper body points and loud, sharp noises like hammers striking a cars frame rail can disrupt measurements.