Best ultrasonic tank level device?

[tech2hyper]

I am looking for the best technology solution for measuring the level in a silo tank that contains fly ash. This by-product is very dusty and fuffy in nature and tends to be somewhat absorbitive for level measurement systems using sound. Fly ash also tends to be abrasive so I would prefer a non-contact solution. A vendor has recommended a Milltronics Airanger SPL so if you have any insite on this device please include in response.

Thanks for any suggestions.