Pump control with two level sensors

VIRUZIE

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V
Join Date
Sep 2012
Location
Hämeenlinna
Posts
9
I have two level sensors I need to connect inside a tank to control the Filling of the tank. The sensors are for upper and lower level respectively. Now the lower level Sensor should switch the Pump ON when it is activated and the upper level sensor does the switching off of the Pump. I have connected these two sensors to 24V DC relay which is working correctly. Now I have to send the information of these two level sensors into a PLC. How should I wire from the relay to the PLC I/O. I am using contrologix from Allen Bradley.

Thank you
 
It's may also be wise to add 2 more sensors. One is a high-high sensor and the other a low -low sensor. I would wire the bottom sensor normally open and the top normally closed.
 
You need latching logic for pump-up operation.

Most of my customers use relay logic, so my diagram is relay logic, not ladder, but if you spend a moment you'll see the set of K contacts (between the junction points) are a latch.

2pq5awi.jpg
 
VIRUZIE said:
I need an interposing relay because the current rating of the sensors are slightly higher than what the Plc can take.
Click to expand...

The sensor current rating is an indication of the maximum load it can drive - since this is greater than the PLC input load, you are OK to drive the PLC input directly
 
Thanks for your advice, anyway I tried to connect the sensors directly to the PLC input caard but my supervisor at work told me it is not the best since it is always better to use a relay in - between the field device and the PLC to protect the PLC. I do not have experience that so I obliged to his idea. Now I have connected the sensors to the relay and they are working perfectly well. I just want to integrate it to the PLC.
I am using compact 24VDC input module from Rockwell. the catalogue number is 1769-IQ16 and the sensor is SOBA HR HY
Thanks a lot, this forum is making me to learn more.
 
Your supervisor knows very little about voltage/current/resistance/impedance and everything else that is important.

No need for a lecture, just take it from me he is walking the wrong road.....

Meaning he is giving bad advice based on a single bad experience that he didn't understand or even comprehend.

EDIT : I didn't (and haven't) check out the spec for your sensors, and have realised they MIGHT NEED interposing relays - hold fire on my comments, your supervisor might be correct for these devices....
 
Last edited:

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