For pumping applications it is important to detect instances where there is a loss of prime in the pump. This is often called dry run , dry well, or low flow. The H100's Under Load protection can be utilized to trip out the VFD and protect the pump if one of these situations occur. This same function can be used for fan applications as a belt break detection. 

Under Load detection is optimized by first performing a load tune on the VFD. Load tuning tunes the VFD to the connected load based on the drives output current, power, and frequency. Since fans and pumps are variable torque loads, the current and power consumption will vary based on the frequency (speed). The Load Tune provides the VFD with some much needed insight on the fan/pump curve. A load tune should be performed after a standard motor auto-tune.  Refer to the below graph to see how a load tune sequence works. 

The Under Load detection works by monitoring the output frequency and output current or power. This is why it is important to perform the aforementioned Load Tune. Once again, since we are applying this to variable torque loads, it is important for the VFD to know what current or power level to expect at a given speed. If that level is low and out of the Under Load bandwidth range for a certain amount of time, the Under Load trip or warning will occur. Below you can see the "UL" detection curve. 

Below is a graphical representation of what happens when the UL detection level is met.  There is both a warning and trip delay time which can be programmed. Additionally, a user may opt to set a relay output to trigger when the UL condition occurs.