The 15-30-15 Rule in Ultrasonic Level Measurements

Written by: Dan Weise

If I’ve heard it once, I’ve heard it a dozen times when talking with a Siemens support guy while evaluating a problematic ultrasonic level measurement application,
“What’s the echo confidence and strength?” “What’s the noise measurement?”

Those are numbers that quantify the echo quality: the floor values for echo confidence and strength and the ceiling value for the noise.   I’d look up the value and the guy on the phone would tell me whether the number was good, bad or so-so.  Finally, someone wrote down what those values should be, and they’re worth filing for future reference.

15-30-15 Note

Echo confidence at maximum range > 15
Echo strength > 30
Noise < 15 value

To find these Echo Quality values for your Siemens ultrasonic level unit, use the table below to navigate to the right parameter:

Multi/Hydro 200/HMI LUT 400 Multi 100 Probe LU LU-01 LU-02 LU-10
Echo Confidence P805, button 8 P805, button 8 P805, button 8 P805, button 8 P805, button 8
Echo Strength P806 P806 P806 P806 P806
Noise Average P807 P807 P807 P807 P807

Navigation target:
3.2.1.    =   3. Maintenance and Diagnostics > 2. Diagnostics >  11. Echo Quality >

Holding the handheld programmer’s #8 button for 4 seconds displays the Echo Confidence:


15-30-15 Picture 4

15-30-15 Picture 5

Questions? Call (800) 953-7626

Learn more about Siemens Ultrasonic Level Technology.

Lesman Instrument Company is the authorized Siemens representative in Illinois, Indiana, Missouri, Paducah KY, Wisconsin, and Michigan’s Upper Peninsula. If you are located outside that area, you can find your local sales office or get technical assistance by calling 800-365-8766.


Dan Weise, Lesman Product SpecialistDan Weise, Lesman product specialist, is an instructor for training classes on process instrumentation hardware, software, and technology.

Dan has been involved in all facets of data acquisition and process instrumentation since 1978, from sales and commissioning to service and support. He’s a long-time member of ISA, and has been with Lesman since 1988.

In his words, Dan’s the guy “who reads all the manuals nobody else reads”. In Lesman customers’ words, he’s the trainer to call if you want to “cut to the SO WHAT of instrumentation”, so it’s easy to understand.


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