What happens in the Desigo system when the V-belt of an extractor fan breaks?
The following figure shows the main information exchanged by the elements concerned, namely:
- Ventilation system sensor/actuator (differential pressure monitor, maintenance switch and single-speed extract air fan)
- PXC program
- Desigo CC plant graphic
- PXM… operator unit
Desigo CC plant graphic page
Desigo CC popup
PXM… Values (in a PXM10 alarm handling is only possible for connected PXCs or PXRs)
PXM… Popup (in a PXM10 alarm handling is only possible for connected PXCs or PXRs)
Time sequence in the example:
- Ventilation system on (e.g., in automatic mode, Cmd.ValPgm = 1), single-speed extract air fan running, fan blades rotating
- The V-belt breaks, the pressure drops, the differential pressure monitor responds (delta p < X) and DPMon.PrVal goes to zero. This activates the alarm monitoring function in the DP monitoring block, and the [TiMonDvn] timer starts counting down.
- After expiry of the time [TiMonDvn], the DPMon block (BI) establishes that DPMon.PrVal (0) is still equal to DPMon.RefVal (0). This is equivalent to the OFFNORMAL state. DPMon.Dstb then goes to 1, and a TO_OFFNORMAL event is transmitted.
- An alarm pop-up window is then displayed, in which the alarm message reads Alarm, Unacked.
- The motor of the single-speed extract air fan is disabled (that is, Cmd.PrVal → 0) because [EnSfty → 1 and Cmd.ValSfty=0, Prio1 Cmd Input]. As a result, DPMon.RefVal goes to 1, thereby activating the alarm monitoring function. After expiry of the time [TiMonDvn], the alarm monitoring function determines that [DPMon.PrVal (0) <> DPMon.RefVal (0)]. The state therefore changes to NORMAL and a TO_NORMAL event is transmitted.
- The alarm display now changes to Alarm = Normal, UnAcked.
- The operator now acknowledges the alarm with Ack in the alarm pop-up dialog box. The alarm display now changes to Alarm = Normal, Acked. The operator sets the maintenance switch [MntnSwi] to Maintenance ON, replaces the fan belt, returns the maintenance switch to Maintenance OFF and resets the alarm with Reset.
- The alarm in the display changes to Alarm = Normal, Unlocked and DPMon.Dstb → 0.
- The fault has been cleared. When DPMon.Dstb = 0, then Cmd.EnSfty → 0 and hence Cmd.PrVal → Cmd.ValPgm=1, that is, the fan motor is enabled. Then, with Cmd.TraSta = 1 (transient state), the fan ramp-up time is allowed to expire, that is, DPMon.RefVal is held at 1 during the transient state. Only after expiry of the ramp up time does DPMon.RefVal revert to 0.
- The ventilation system is already running (from step 6 on), that is, the fan blades start rotating, the pressure builds up and the differential pressure monitor detects delta p = X again, that is, DPMon.PrVal → 1. The alarm monitoring function is active again. After expiry of the time [TiMonDvn], this determines that there is no alarm condition present, because [DPMon.PrVal(0) <> DPMon.RefVal (1)]. The system then operates 100% correctly as described under step 1 above.
To simplify the time chart shown above, the connection to DPMon.EnAlm has not been included.