triplewhammy
Member
Hello everyone, first timer here. I'm a senior electrical engineering student having a slight issue with our design project. An A-B MicroLogix 1000 PLC is automating various components of a water filtration system (everything operates on 24V DC). One of these components is a pump. To drive the pump, we have an output from the PLC going to an external relay. Once the relay contacts close, the pump is to kick on (we also have a fuse in series as well).
The problem is, when the logic calls for the PLC output to energize, there is a spark on the relay and it clicks on and off, causing a fault on the PLC. Apparently, the PLC is unable to close the external relay to turn on the pump. HOWEVER, if we manually connect the relay contacts (there is a pushbutton on the relay) the pump will kick on and then when we let go, the PLC will KEEP the relay on (as it should, until specific logic turns it off again). The PLC is having no problem keeping the contacts closed, nor is there a problem once it has to turn it OFF, but for some reason it can't close the contacts on its own...it causes a fault, clicks, "backfires", then tries again over and over.
Anyone have any idea why the PLC can't initially close the external relay contacts? (keep in mind it can keep them closed once manually closed).
Big thanks in advance!
Josh
The problem is, when the logic calls for the PLC output to energize, there is a spark on the relay and it clicks on and off, causing a fault on the PLC. Apparently, the PLC is unable to close the external relay to turn on the pump. HOWEVER, if we manually connect the relay contacts (there is a pushbutton on the relay) the pump will kick on and then when we let go, the PLC will KEEP the relay on (as it should, until specific logic turns it off again). The PLC is having no problem keeping the contacts closed, nor is there a problem once it has to turn it OFF, but for some reason it can't close the contacts on its own...it causes a fault, clicks, "backfires", then tries again over and over.
Anyone have any idea why the PLC can't initially close the external relay contacts? (keep in mind it can keep them closed once manually closed).
Big thanks in advance!
Josh