Is the PING temparature sensitive?

pwillard

I have my version of the garage assistant ( from completed projects ) happily assisting me everyday when I get home.· I've noticed lately that when the temperature is very cold outside ( naturally a bit warmer in the garage... but not by a vast·amount ) it seems to indicate· erratic or incorrect distance... later in the day... when it's warmer... all is normal.

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There's nothing like a new idea and a warm soldering iron.

Bruce Bates

pwillard -

Your problem may simply be a matter of physics and weather. The speed of sound itself will vary based on any number of environmental factors. Extremes of temperature, humidity, atmospheric pressure and wind speed may all play a part, to one degree or another, in changing it.

So, somewhat regardless of whether the PING-)) is temperature sensitive itself, there may well be variations which are external to the unit.

Regards,

Bruce Bates

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Phil Pilgrim (PhiPi)

Varying atmospheric conditions can play havoc with ultrasonics if accuracy is important. I once designed an automated elevator that raised an lowered a vat of liquid urethane to keep the level constant with respect to fishing lures being conveyed into it for coating. The idea was to coat up to, but not including, the top loop; so the required accuracy was pretty high. I used an ultrasonic sensor, after being assured by the business owner that neither the ambient temperature nor the humidity would vary by more than a percent or two. Well, both varied a lot more than that, rendering the sensor useless for the accuracy required.

One possible solution is to install a target at a known distance that can be rotated into and out of the field of view (using an RC servo, perhaps). This target can be used to calibrate the system periodically, so what you are measuring is the ratio of two distances: one known, and one unknown. The atmosphereic effects will then cancel out.

-Phil

Steph Lindsay

Interesting! How cold is cold? Close to or below freezing? The device is not industrial-rated, we give it a range of 0 to 77 degrees C. If it gets really cold in your garage, perhaps some of the components on the board get unhappy, such as a resonator. I would also suspect condensation buildup on the transducers, and if your device is battery-operated, perhaps it's not getting enough power when the batteries are chilled?

We do address temperature's effect on the speed of sound in air briefly in Chapter 2, Activity #5 of Smart Sensors and Applications, looking at percent error measurements. Temperature has a greater effect than either humidity or pollution in the speed of sound. But the percent error from room temperature to freezing is only about 4.5% I think.


-Stephanie

pwillard

Well, It hasn't really been freezing here in the North GA Mountain area... though I do read External Temperature low of 33.9 yesterday. My garage is "internal", so I assume it's always around 40-50 overnight, seldom less. I guess I could rig up a DS18S20 and have a real look at it overnight. On warm nights though... no effect... but nights when it's been in the low 30's... it's saying my car is WAY to close at 6:30 AM and JUST RIGHT when I arrive home at 4:30. (ambient external temperature @ 4:30 PM is 58.

I guess I'm not really talking extremes here.

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There's nothing like a new idea and a warm soldering iron.

Tracy Allen

Links that may be of interest:

Is PING sensor temperature compensated?

howmuchsnow?

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Tracy Allen
www.emesystems.com

Shawn Lowe

Boy, this Chris Nafis did an excellent job of documentation. I imagine this is for a school project, or maybe this gentleman is just THOUROUGH!

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Shawn Lowe


Maybe I should have waited to do that......