A07821 — Monitoring underspeed threshold fallen below alarm

The manuals call this message Monitoring underspeed threshold fallen below alarm: the drive has detected that its speed has fallen below the alarm threshold for the lower speed. That threshold is speed threshold 2 (p2155), used together with the hysteresis p2140. The monitoring is active either because it was enabled with p2149.6 = 1, or because it is activated automatically internally for a separately excited synchronous motor in closed-loop torque control without an encoder (p1300 = 20, p1501 set). While the speed is below the threshold, status bit r2197.1 = 1. Whether the alarm is actually output depends on the control mode: in closed-loop control without an encoder it is only output for an excited motor (r0056.4 = 1); in closed-loop control with an encoder it is always output. A07821 is an alarm without an automatic shutdown and without an acknowledgement requirement.

• The speed has fallen below the alarm threshold for the lower speed (speed threshold 2, p2155, with hysteresis p2140).
• The monitoring is active: it was enabled with p2149.6 = 1, or it is automatically active internally for a separately excited synchronous motor in closed-loop torque control without an encoder (p1300 = 20, p1501 set) — in the second case the alarm can appear without explicit activation.

1. Check the parameterization of the threshold: p2155 and p2140.
2. If the parameterization is correct, reduce the load if required.
3. For generator applications, switch on an additional unit.

• p2149 (Monitoring configuration): set bit 6 to 1 (p2149.6 = 1) to activate this underspeed monitoring.
• p2155 (Speed threshold 2): holds the lower-speed threshold whose parameterization you check when the alarm appears.
• p2140 (Hysteresis speed 2): the hysteresis belonging to that threshold, checked together with p2155.
• p1300 (Open-loop/closed-loop control operating mode): value 20 is the closed-loop torque control mode in which the monitoring is automatically active for a separately excited synchronous motor without an encoder.
• p1501 (BI: Change over between closed-loop speed/torque control): set together with p1300 = 20, it identifies the torque-control mode in which the monitoring switches on automatically.

A07821 requires no acknowledgement and does not force the drive to shut down. It clears itself once the speed is back above the threshold; status bit r2197.1 = 1 shows that the value is still below it. If the alarm keeps returning, check the threshold values in p2155 and p2140, reduce the load if required, and for generator applications switch on an additional unit.