Trouble making multiple measurements with PING

Involute1344

I'm making three measurements in quick succession with the PING so I can toss out the high and low values to cut down on spurious readings. Regardless of the delay I use between the subsequent readings (from 250 us to 1.5 ms), however, the second and third readings bounce around a lot (by an order of magnitude); the first reading tends to be pretty accurate. Any idea why the subsequent readings are so variable? By delay I mean the time from when the echo return pulse goes low until I send a new trigger pulse. Thanks.

Phil Pilgrim (PhiPi)

Is it safe to assume that the second and third return times are shorter than the first? If so, it's because you're still getting echoes from a prior transmission. Set your delay time longer.

-Phil

Involute1344

Sometimes one will be shorter and one will be longer. In any event I pushed the retrigger delay out to 1.8 ms and that seems to have fixed the problem.