Vega VEGAMET 391 Operating Instructions Manual

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478 Application examplesVEGAMET 391 • 4 … 20 mA/HART36032-EN-170907triggered after the enquiry period. The enquiry period is started asdescribed above when the relay is switched on.Switch-on behaviour of pump control 2When the signal conditioning instrument is switched on, the relays areat first in a switched-off status. Depending on the actual input signaland the switched-on period of the individual relays, the following relayswitching conditions can occur after the start procedure:• Input signal is higher than the upper switching point -> Relay withthe shortest switched-on period is switched on• Input signal is between lower and upper switching point -> Relayremains switched off• Input signal is smaller than the lower switching point -> Relayremains switched off8.3 Pump control 3/4 (sequentially controlled)Pump control 3/4 is used to control several pumps with the samefunction alternately and in a fixed sequence. In case of increasedpumping requirement, all pumps can also run at the same time, independence on the entered switching points. This measure achievesan even utilization of the pumps and increases operational reliability.All relays with activated pump control are not assigned to a certainswitching point but are switched on and off alternately. When a switch-on point is reached, the signal conditioning instrument selects therelay that is next in the sequence. When a switch-off point is reached,the relays are switched off in the sequence they were switched on.Via the digital inputs, possible fault signals of the pumps can also beevaluated. You can find the description of this in the application exam-ple "Pump control 1/2" under "Pump monitoring".This pump control system offers two different options:• Pump control 3: The upper switching point determines the switch-off point for the relay, whereas the lower switching point deter-mines the switch-on point• Pump control 4: The upper switching point determines the switch-on point for the relay, whereas the lower switching point deter-mines the switch-off pointThe sequence cannot be changed, the relay with the lowest index isswitched on first, then the relay with the next higher index. After therelay with the highest index, the relay with the lowest index follows, forexample Rel. 1 -> Rel. 2 -> Rel. 3 -> Rel. 4 -> Rel. 1 -> Rel. 2 … Thesequence applies only to those relays assigned to the pump control.In a waste water disposal system, a sump should be pumped emptywhen a certain level is reached. Three pumps are available for this. At60 % level, pump 1 should run until the level has fallen below 10 %.If the 60 % point is exceeded again, the same task is transferred topump 2. In the third cycle, pump 3 is activated; after that, pump 1again. If the level continues to rise despite operation of a pump, anadditional pump switched on when the level exceeds the 75 % switch-Functional principleExample