A 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 distance.  That 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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