If there is a flow switch (digital output) or flow sensor (analog) present, then run-dry conditions occur when the flow switch gives a no-flow signal or the flow sensor indicates zero flow.
But when you do not have a flow switch or sensor, then the only option is to use flow estimation. Flow estimation can be done based on power (for known power and defined "power vs flow" curve ATV can calculate the flow) or based on pressure measurement (for measured pressure and defined "head vs flow" curves ATV can calculate flow).
So flow estimation requires at least one pump curve to be entered. The best of both curves are entered.
Dry-run monitoring requires that no-flow curve is also defined in ATV, unless a flow switch or sensor is used. No flow curve represents the situation when there is no flow, but water is present in the pump. For example, the valve on the outlet is closed.
For a no-flow curve it is necessary to define 2 points :
- Low point [NFLS, NFLP] where NFLS is low speed and NFLP is power at low speed.
- High point [NFHS, NFHP] where NFHS is a high speed and NFHP is power at high speed.
Run-dry warning or fault is triggered when the estimated flow (in fact corresponds to the power that ATV measures) is below DRYX * no flow curve. The factory setting for DRYX is 70% so if the measured power is below 0.7 * no-flow curve, a run dry warning or fault will appear. DRYX parameter helps to distinguish two different situations :
- no flow but water is present in a pump (power consumed is greater than in the second case)
- no flow because of no water is present (power consumed in lower).

Julkaistu: Schneider Electric Suomi