# A Question about ultrasonic range meters

Discussion in 'Electronic Design' started by Sara, Jul 14, 2006.

1. ### SaraGuest

Dear friends,
I'm working on a project for measuring the level of liquid in a tank
with ultrasonic sensors.
In this project i need a measurement resolution about 1mm and the
maximum range of measuring is about 4m.
First I want to know if resolution depends on the frequency of the
sensor or the electronic circuit that measures the time of going and
returning of signal.
Second I have found an article that has measured the level with phase
shift with great resolution but the maximum range is 90cm.I will
resolution and the way one can extend the maximum range to 4 m.

Regards
S.Azimi

2. ### Guest

Have several sensors spaced 90cm apart, with a float switch on each so
you can determine which sensors are not presently covered by liquid.

3. ### John FieldsGuest

---
What's the liquid and what's the minimum range?
---
---
It depends on both, as well as on the change in the velocity of
propagation of sound through the medium, which in turn depends on
the density and temperature of, and pressure on, the medium.

Also, you don't mention whether you'll be measuring through the
liquid or through the space in the tank above(?) it.
---

4. ### Rene TschaggelarGuest

I guess the range depends on whether the signal can
travel in a tube or whether is is in the open.

Rene

5. ### JoergGuest

Hello Sara,

Both. Resolution goes up with frequency but your electronics must be up
to snuff, especially if you want to extricate phase angles. Most likely
you have to become very familiar with I/Q mixing and detection. Analog
Devices and Mini-Circuits carry the relevant parts for that.

Why was the range limited? What's the liquid? How do you focus the beam?

Anyway, before you get too carried away with achievable resolution look
at the fluid to be measured. I'd bet that it's ultrasonic properties
will not be constant over pressure, temperature etc. Look closely at the
sound velocity in it and how it changes with other parameters. This data
isn't always published but can be measured.

Then there is a whole other topic to ponder: Gas micro bubbles in the
liquid. These will scatter the ultrasound signal no matter how good you
focus the beam and influence the velocity of sound.

7. ### SaraGuest

Hello John,
Thank you for your good information.

The liquid in the tank is petrol or gasoline and the minimum range is
20cm.
I'm measuring the level of liquid through the air(the space above the
liquid).I want ot know if it is possible to gain 1mm resolution with
40khz ultrasonic sensor?The name of article is "Extending the accuracy of ultrasonic level
meter" at :
stacks.iop.org/MST/13/598 by P.Olmos.And also i found another article
that is "Fast processing techniques for accurate ultrasonic range
measurments"By B.Barshan which explained four methods for measuring TOF
one of them is sliding-window which is exactly the thing I'm looking