# Logic diagrams for relays help

• EverGreen1231
In summary, the picture shows a circuit diagram for a relay with an input that is high and one that is low. The circuit is designed to protect the relay by disabling it if one of the inputs goes high for a set amount of time.
EverGreen1231
Good morning,

I'm looking at some logic diagrams for relays and have encountered something that I've never seen before. I haven't looked on the internet extensively since I thought the folks here at the forums would be able to answer my question more quickly. My experience with logic is limited (I'm more of a Power guy) so I've not looked at much outside of classes on the subject; so if anyone could explain to me what this little thing in the picture below does, I'd be much obliged.
http://forum.gon.com/picture.php?albumid=8041&pictureid=44664

-Tyler.

What picture?

From what industry does that symbol come ?

Instrument Society of America's standard symbols are in 5.4 table 3 here
https://esimezica.files.wordpress.com/2011/02/s_51.pdf

and yours rather resembles a converter block, element 20 on page 25 of the pdf.

Surely there are some cryptic clarifying notes nearby ? Can you scan and post the page ?

EverGreen1231
jim hardy said:
From what industry does that symbol come ?

Instrument Society of America's standard symbols are in 5.4 table 3 here
https://esimezica.files.wordpress.com/2011/02/s_51.pdf

and yours rather resembles a converter block, element 20 on page 25 of the pdf.

Surely there are some cryptic clarifying notes nearby ? Can you scan and post the page ?

High Power Transmission Protection and Controls. I have someone at work that should be able to explain it to me, but they won't return 'till tomorrow. In the mean time, there aren't any notes around, but the full logic may help someone come to an explanation. I've spent some time analyzing the logic so as to gain some understanding of how these circuits are behaving with various inputs, but I'm at a cross-roads of understanding.

Here's the component in a circuit for context...

As you can see, the circuits aren't really that difficult to understand; but without knowing exactly what this piece does, it's difficult for me to say I understand it completely.

Would it make sense for it to be a memory element, to provide the lockout ?

EverGreen1231

I think that memory would be an accurate description, but timer might be a little better. I found out that the SV stands for Schweitzer Variable. If you have one in a circuit where the input to the SV is RELAY ALARM + !TRIP COIL MONITOR + STATION DC NOT GOOD and one of these inputs goes to high for, let's say, 130 cycles; then the SV will allow current to flow. If the SV has "0" as its set value (as in the example in the picture), then it will allow complete transparency between the input and output sides. I suppose it's there only to set a timer if it's needed in any particular application. This signal will pass through several other gates that provide inputs to an SR latch. The output of this latch will let the relay know if a HOT LINE TAG has been applied. Meaning the breaker will go straight to lockout if a limb hits the line or there's some other type of ground fault (it'll also make the relay more sensitive to ground disturbances).

## 1. What are logic diagrams for relays used for?

Logic diagrams for relays are used to visually represent the logical connections between input and output signals in a relay system. They help engineers and technicians understand the functionality and operation of a relay system.

## 2. How are logic diagrams for relays created?

Logic diagrams for relays are created using standardized symbols and notation, such as IEEE or IEC standards. These symbols represent different types of relays, contacts, and connections, and are arranged to depict the logical flow of signals in a relay system.

## 3. What is the purpose of using logic diagrams for relays?

The main purpose of using logic diagrams for relays is to aid in troubleshooting and understanding the operation of a relay system. They also help in designing and modifying relay systems, as well as in training and educating technicians and engineers.

## 4. Can logic diagrams for relays be used for any type of relay system?

Yes, logic diagrams for relays can be used for any type of relay system, including electromechanical, solid state, and microprocessor-based relays. They are a universal tool for understanding and analyzing the logic of relay systems.

## 5. Are there any limitations to using logic diagrams for relays?

One limitation of using logic diagrams for relays is that they can become complex and difficult to interpret in large and intricate relay systems. Additionally, they do not show the physical layout or wiring connections of the relays, and therefore should be used in conjunction with other documentation for a complete understanding of the system.

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