Ultasonic sensor giving false readings?

[Jak24]

Hi

I have a couple of srf05 ultrasonic sensors,
they worked fine for a while, but then i realized that occasionally
they gave false readings , for example if the wall was 50 cm away it gave readings like this:
50, 50, 50, 178 , 50 , 49, 50, 50 , 50 , 145 , 50
but then other times it gave continuously bad readings
I believe the reason it the viewing angle , because if it looked at exactly 90degrees straight at the wall it mostly
gave good readings, but as soon as the angle changed more than 10 degrees from looking directly at the wall
it gave readings that were of more than 100 cm
is the angle of the sensor really that big an factor?
the program i used for it was the example program on the website:
http://www.robot-electronics.co.uk/ 
so i doubt the program is at fault.
so my question is are all ultrasonic sensor the same, in that  the angle compared to the measured wall/object
is a big influence? , and would the method of the ultrasonics communication matter?( I2C, or digital signal?)

Thanks

Regards
Jak24

[madsci1016]

so my question is are all ultrasonic sensor the same, in that  the angle compared to the measured wall/object
is a big influence?

No, they can have different beam widths. Here's the different EZ models.

and would the method of the ultrasonics communication matter?( I2C, or digital signal?)

No, unless your sensor is faulty.

There could also be a source of interference. Try changing the location of your test.

[waltr]

I would believe that the wall angle, especially a very smooth wall, can affect the distance reading.
Remember that it works by measuring the time from the transmitted pulse to the when the pulse is received. If the enough of the pulse is not reflected back to the receiver but is instead reflected off to a different angle then off another object, think of two walls meeting in a corner, before getting to the receiver then the distance would be farther.

A smooth surface would reflect almost all of the pulse according to the rules of reflection, think of a mirror, whereas a rough surface scatters and enough of the pulse makes it directly back to the receiver.