Posts Tagged false echo suppression

Why doesn’t my LR560 radar’s analog output match the displayed level value?

Siemens SITRANS LR560 radar level transmitterA customer who had had lots of experience with Milltronics and Siemens ultrasonics was installing his first SITRANS LR560 radar level transmitter.  They had worked with it in the shop beforehand, going through most of the settings.  They even tested it by setting it up to shoot against a file cabinet and used a tape measure the check the indicated distance value.

Everything checked out OK in the shop.

When they installed the transmitter on the top of the bin, they changed the transmitter’s sensor mode parameter from the distance mode they used in the shop for testing to level mode.  After aiming, the level value shown in the local display was dead nuts on, but the 4-20mA signal going back to the control room was way off.

The bin was a third full. The 4-20mA showed it about double that.  Not only that, the 4-20 was going in the wrong direction.  The bin was emptying and the HMI reported an increasing level value.  Someone realized that an inverse-acting output was typical of a distance value, so they reconfigured the sensor mode to distanceThat got the 4-20mA much closer to a distance value, but it was still not exactly what it should be, and besides, the goal was to read level, not distance, in the control room.  What was going on?

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The Impact of Background Echoes on Ultrasonic Level Measurement

Photography is a pretty good way to illustrate the importance of background.

Look at the two photographs here. In one, the background is minimal, and focuses your eye on the subject matter. In the other, the background seriously detracts from the subject. Where should you be focusing? What’s most important?

Non-intrusive background makes focus point clear

Hard to discerne the difference between the action and all the stuff happening in the background

 

But unlike photography, where a good background helps you focus on the subject, in the world of non-contact ultrasonic level measurement, even a “good” background has a negative influence.  Background never contributes to a level reading, it only detracts. But Siemens has a built-in function to “cure” for the influence of backgrounds in their level devices. Read the rest of this entry »

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February 2: A day to look back

Yesterday and today, people all over Chicago and the Midwest were looking at pictures from last year. We had 22″ of snowfall in one day. The roads were closed. The airports were closed. Even the Lesman offices were closed. And today’s weather forecast? 45°… in Chicago… in February.

This morning in Pennsylvania, a groundhog named Phil came out, looked back, and saw… his shadow.

All this looking back made me a little reflective myself. I’ve been writing this blog for about 6 months now. So I thought I’d take a minute and recap the articles people keep coming back to read:

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What is false echo suppression?

A few weeks ago, I wrote about problems a customer encountered trying to move a functioning radar level device from one tank to another. With a little light reading of the user manual, and one change on the radar, the situation was resolved. 

People are usually familiar with the concept of false echo suppression: looking at a tank and mapping out the obstructions that can cause false readings, like baffles, ladders, tank braces. But the Siemens products we work with do it a little differently. It’s a built-in feature on Siemens ultrasonic and radar level devices, and only takes five minutes to run.

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Challenge moving a Siemens radar level gauge

Ran into a situation last week that taught me an important lesson.

A customer took a tank out of service for major repairs, so they moved the Siemens radar level transmitter to a different tank.   Even though the radar unit performed flawlessly on the first tank, they ran into difficulty getting the correct level readout in its new installation.  

The mechanical guy had moved and remounted the transmitter.   The I&E tech had wired it correctly, and then did a master reset before starting a fresh configuration.  After going through the configuration, he couldn’t get a valid level readings in the upper fourth of the tank level.

The second tank was near its full level and the technician (properly) wanted to wait to do an Auto-Learn scan until the tank level approached empty.  In the meantime, we were all scratching our heads trying to figure out why the upper level readings were not correct.  

In frustration, I finally resorted to pulling out a manual . . . Read the rest of this entry »

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