I RL vs LR Circuits: Low-Pass/High-Pass Filters Explained

[terryds]

Is there any difference between RL vs LR circuit? Which one is for low-pass/high-pass filter?

Please help

 

[cnh1995]

Is there any difference between RL vs LR circuit? Which one is for low-pass/high-pass filter?

Please help

They are one and the same.

 

[terryds]

They are one and the same.

Really? But RC and CR are different, RC is a low-pass filter and CR is a high-pass filter.

 

[davenn]

Really? But RC and CR are different, RC is a low-pass filter and CR is a high-pass filter.

they can be both ways ... so don't get trapped

have a read of this
http://www.uniroma2.it/didattica/Experimental/deposito/Filters.pdf

I can actually find no reference to a LR circuit

it always refers back to RL filter circuits
https://en.wikipedia.org/wiki/RL_circuitDave

 

[davenn]

so your 4 types are

RC, CR, RL, RLC

 

[NascentOxygen]

Is there any difference between RL vs LR circuit? Which one is for low-pass/high-pass filter?

RL is high pass, LR is low pass. Brevity for its own sake is generally discouraged.

 

[davenn]

RL is high pass, LR is low pass. Brevity for its own sake is generally discouraged.

why can I only find references to RL and not LR ?
do you have any references please?

 

[tech99]

why can I only find references to RL and not LR ?
do you have any references please?

These filters work by potential divider action. We can have series R and shunt L, giving high pass action, or the converse. We can also connect the filter either way round. It is important to consider the impedance (usually resistance) of the source and the load, so that we are considering the full circuit.

 

[sophiecentaur]

RL is high pass, LR is low pass. Brevity for its own sake is generally discouraged.

Frankly, I would not make any assumption about the actual layout of an LR or and RL circuit, if there was no information provided about how it has been connected. Wait till you see the circuit diagram and then you have a chance.
Trying to generate special rules for the meanings of letters in particular orders is a dodgy pastime and very likely to produce as confusion as enlightenment. Leave it to lexicographers and etymologists.

 

[NascentOxygen]

Assumptions are no substitute for unambiguous specifications. But in this case there can be only one interpretation to the difference between an RL and an LR, particularly in light of the answer options being given.

 

[sophiecentaur]

in light of the answer options being given.

Personally, I wouldn't want to get involved in a system that appears to force a reader into such a bad choice with such open ended assumptions. The only thing one could say about RL or LR would be that the associated time constants would be the same. (Same comment for RC and CR)

 

[davenn]

and I am still left without an answer to my question in post #7

 

[sophiecentaur]

why can I only find references to RL and not LR ?

It shows that 'the system' actually has a certain amount of sense, perhaps.
The more familiar RC / CR is a terminology which, as I have said before, is confusing. In fact it is bad and makes assumptions about the connection and orientation of the R and C in a circuit that are not justified. How would one describe the filter function (HP /LP) if the source for the circuit was more constant current than constant voltage, for instance? And would it always be the case that the output connection would always be across the second of the pair of letters?
RL circuits do not tend to be discussed or used anything like as much and, when they are, it is probably by more informed users or designers. They have avoided the problem by just not going down that road.
You could say I'm being elitist but I must insist that using 'unofficial' conventions and terminology will always risk errors. EE is littered with similar fuzzy terminology which has been introduced in a misguided effort to make it more 'approachable'.

 

[NascentOxygen]

I can picture it being a local shorthand, perhaps introduced by a lecturer for his introductory class on passive filters, and not intended to be used beyond that. Best kept inhouse, and used only with those who've been inducted to interpreting what's meant.

Of course, it could even be debated whether substituting RC filter for RC LPF is actually shorthand at all.

I fear we've lost the OP.