looking for help with my PLC class.

[Freshlife706]

doing a lab for my plc class and reaching out for help to try and understand.

 

[ptonsparky]

Which rung controls the red light?

 

[ptonsparky]

Where is the variable?

 

[jim dungar]

What part of the compare function is giving you problems?
Dont you have a variable value being compared to a constant value?
Doesn't the thumb wheel binary input get decoded into someplace?

 

[Freshlife706]

so would the variable value just have to be 5 to be equal to the constant value?
i was thinking that variable 2 would have something to do with the BCD but 2 = 0010 and 5= 0101

I'm just reaching out because the teacher that i have has no idea how to explain this to my class and gets nowhere, the book that we have does not explain this process at all.

 

[ptonsparky]

Nm.

 

[jim dungar]

so would the variable value just have to be 5 to be equal to the constant value?
i was thinking that variable 2 would have something to do with the BCD but 2 = 0010 and 5= 0101

I'm just reaching out because the teacher that i have has no idea how to explain this to my class and gets nowhere, the book that we have does not explain this process at all.

Ignore the actual value of the thumbwheel shown in rung one.

The question simply asks what value of the thumbwheel is need to fulfill the compare function for the red light in rung #3.

 

[mtnelect]

Greater than 1 but less than 2

 

[jim dungar]

Greater than 1 but less than 2

Not according to the logic provided which has three rungs containing an Equal compare, a Less Than compare and a Greater Than compare with corresponding colored lights.

 

[Freshlife706]

Not according to the logic provided which has three rungs containing an Equal compare, a Less Than compare and a Greater Than compare with corresponding colored lights.

so on rung 3, does the variable value just have to equal to the constant value to make the red pilot light to turn on?

 

[jim dungar]

so on rung 3, does the variable value just have to equal to the constant value to make the red pilot light to turn on?

Yes.

 

[drktmplr12]

does the class understand how to read binary?

if not, there's the problem

 

[jim dungar]

does the class understand how to read binary?

if not, there's the problem

That is not part of the OP question, which can be answered solely be looking at rung #3.
Thee program might not even be running, so none of the rungs may be displaying real vaules at all.

 

[Freshlife706]

does the class understand how to read binary?

if not, there's there's the problem

we are only on chapter 3 of the textbook and it doesnt really talk about reading it yet, just how to convert from binary to hex from octal to deciaml and so on.

 

[Freshlife706]

That is not part of the OP question, which can be answered solely be looking at rung #3.
Thee program might not even be running, so none of the rungs may be displaying real vaules at all.

okay well that makes alot of sense so

 

[drktmplr12]

That is not part of the OP question, which can be answered solely be looking at rung #3.
Thee program might not even be running, so none of the rungs may be displaying real vaules at all.

OP followed up and stated that the instructor could not this to the class so there is a fundamental miscommunication or misunderstanding. That prompted my response.

The question is what value the thumbwheel will turn on the light, not what value of Variable_Value. One needs to know how to read a BCD to complete the problem. If the class doesn't understand BCD, they can't interpret what a FRD instruction is doing.

 

[petersonra]

the FRD instruction just converts a binary input coded in BCD to a standard integer.

 

[drktmplr12]

the FRD instruction just converts a binary input coded in BCD to a standard integer.

if one can't read a BCD, one can't understand what an FRD is doing. It might as well be converting Sanskrit to an integer.

 

[petersonra]

if one can't read a BCD, one can't understand what an FRD is doing. It might as well be converting Sanskrit to an integer.

one does not need to understand bcd to understand that the result is a standard DINT.

 

[jim dungar]

if one can't read a BCD, one can't understand what an FRD is doing. It might as well be converting Sanskrit to an integer.

And the OP question was dealing with the value needed in rung 3 for the red light, so it must have been about the Compare function.