Unwanted end result with SLC-5/03

ceilingwalker

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ceilingwalker
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Mar 2010
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Good day all. I have a situation with a program that I can't find the root cause. I have a conductive level sensor that that is supposed to be a "1" when level is good and a "0" when it is low. I've attached the program and the ladder in question is number 4, rungs 3,4 and 5. Everything works fine until a tank gets a low level. It then de-energizes the relay on the level sensors module. Everything works great. Now, when the tank is re-filled, the bit doesn't seem to want to unlatch itself and continues to put a "1" in the inputs bit box and I have to physically disconnect the sensor then get it to reset. I'm thinking it may be in the sensors control module and not the ladder logic but I would like to know if someone wouldn't mind checking my logic to see if I'm missing something that could be causing this. Thank you.
 
If the physical input I:1/14 I:1/15 and I:9/8 is staying a high/1/on then there is power on the input. Is that what is happening? you should also see the input on the card. I see that both input carda are the same kind and should be ok. looking more I see you are using OTU Try changing them to OTE instead. same adress is fine. make the b41:0/3 b41:0/4 and the b41:0/5 OTE instead of OTU.


Paul
 
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If it is a relay output from the sensor then it is odd. Provide the model/part number of the sensor and the input module and your wiring. But if it is a solid state output then there may not be enough current load presented by the input.
 
Last edited:
ceilingwalker said:
Good day all. I have a situation with a program that I can't find the root cause. I have a conductive level sensor that that is supposed to be a "1" when level is good and a "0" when it is low. I've attached the program and the ladder in question is number 4, rungs 3,4 and 5. Everything works fine until a tank gets a low level. It then de-energizes the relay on the level sensors module. Everything works great. Now, when the tank is re-filled, the bit doesn't seem to want to unlatch itself and continues to put a "1" in the inputs bit box and I have to physically disconnect the sensor then get it to reset. I'm thinking it may be in the sensors control module and not the ladder logic but I would like to know if someone wouldn't mind checking my logic to see if I'm missing something that could be causing this. Thank you.
Click to expand...

It is late here now - i will open this up tomorrow and take a look.

First to mind is have you actually monitored the physical input to see if it is going on and off as the level dictates? Some conductive probes in some materials get "coated", and will still say covered for a long time after it is uncovered.

Assuming your input is signaling OK, there must be a logic issue, and if no-one else can answer your query, i'll get back after a much-needed sleep.....
 
I have no problem with the ladder shown (I can't open the RSS file right now). Presumably from the name the bits are set from the HMI and reset if there is a problem.

Definitely check the actual input, look at the light first to see if it goes off or not. It's probably an electrical problem or possibly the 'coating' problem as mentioned by daba.
 
OH no the dread OTU.... JUST kidding. level sensors,probes.float switches are notorious for just this kind of thing. havent looked at the logic but if it goes off when you disconnect the input the logic seems to work check out or replace the sensor. It could be that you may be better off with a float or ultrasonic sensor read the specs on your sensor and see if it is compatible with your liquid. best of luck, steve
 
If the bits are latched from the HMI, I would check what type of button you are using on the HMI.

The only way the bit can stay on is if the HMI is latching the bit, and then no matter what code you have to unlatch that bit in the PLC, the HMI will always overwrite it.

Mark
 
MarkNightingale said:
If the bits are latched from the HMI, I would check what type of button you are using on the HMI.

The only way the bit can stay on is if the HMI is latching the bit, and then no matter what code you have to unlatch that bit in the PLC, the HMI will always overwrite it.

Mark
Click to expand...

You're exactly right. The unlatch does just as you mentioned, the HMI latches the switch on, the switch can then only be unlatched by the logic the way it is written. I read everybody's input, then studied the logic, now I understand it. The issue turned out being a problem with dip switch settings on the level sensor board's. Thank you everyone for your help. I keep hoping my Quick Panel will die soon so I can purchase a Red Lion or anything but a Quick Panel.
 

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