Symbols 1

[itsmoked]

I'm drawing a schematic for a multiple pump hydraulic control system I'm designing. It has the usual pesky front panel covered with a matrix of the typical, grossly expensive, 30mm type selector switches.

I will be using some of those switches with mind numbing contact specifications. Essentially a double throw(center off) triple pole, spring return to center.

Keep in mind in the spirit of all these switches they are ALL internally and externally purely single pole, single throws that you must actually jumper to make single pole-double throw.

The Old Schematics I am upgrading from show these in single pole. I find the symbol used to be horrible and unclear.

Can someone direct me to a "good" symbol or where I could forage for one.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[electricpete]

How about the conductor comes in from the left representing the common point and goes to the base of an arrow. The arrow has three positions for it's end: Hand, Off, Auto. This is shown by drawing an open circle for Hand, Off, Auto on the right side of the arrow so if you pivoted the arrow about it's base it could connect to any of those open circcles. The Hand open circle is connected to the upper right condeuctor. The auto open circle is connected to the lower right conductor. The off open circle has no connection.

A picture would be worth a thousand words.

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[electricpete]

Like this?

http://home.houston.rr.com/electricpete/switch.ppt

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[itsmoked]

Dang fast response electricpete.. but... you have described(unless I'm too dense) essentially a (three) terminal switch when if you look at the above picture you see this type of switch has (four) terminals. When I try to come up with a nice symbol....I don't, just like the bloke who did this drawing.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[electricpete]

Yeah, I thought you'd be familiar with it if it was that easy.

I think for this situation we just show a contact table.
For example
____Hand_Off_Auto
1-2__X___________
3-4____________X_
With note nearby "Spring return to Off"


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[electricpete]

I forgot that you also have to give the switch a designation, for example S1. Put S1 next to the = contact symbol and then 1 and 2 next to the circular terminals directly on top/bottom of the contact symbol. Then create another contact symbol = labeled S1 again, but this one has contact terminal circles labeled 3 and 4.

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[electricpete]

... and of course the table has to be labeled as S1 also so they know the table describes the behavior of the contacts.

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[electricpete]

My description from memory was poor. An example from our plant drawings here. First page is table, second page gives example contacts:

http://home.houston.rr.com/electricpete/switchtable.ppt

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[electricpete]

Maybe that was an over-complicated example...

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[electricpete]

The essential logic could be displayed without the first two columns "block" and "contact". What is needed is the third column which gives contact numbers corresponding to the contacts in the drawing. Then for each contact number, the X's denote which conditions the contact is closed.

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[itsmoked]

I hear you electricpete... That extra abstraction of a table doesn't make me lunge for your tabular switch.. I understand it and it's clean... But I wish I didn't have to use a table. Do you think the table is clearer than the original symbol in my pic? (not sure)

Here's some stabs at it I just did. (I'll admit some were in the dark) {{the open and close do not refer to the switch state!! just the function}}

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi itsmoked and electricpete;
Actually both conventions are correct but refer to different devices.
The original symbol refers to what used to be the oiltight line of pushbuttons and selector switches. There are a lot of newer designations for bushbutton lines now in use.
The symbol you are using is as you state, two single pole contact blocks mounted on a single operator (Selector switch or push button.) There is another variation that is a double throw. The symbol is similar, but only one horizontal line is shown to indicate the movable contact and the dots are shown closer together. In industrial control diagrams, the symbols you have shown are widely used and widely understood. You will find those symbols used in the motor starter wiring diagram booklets given out by most motor control manufacturers.
In my GE Control catalogue, 1995 issue, the convention is used for both the wiring diagrams of the motor starters and to describe the action of the various push buttons and selector switches.
A couple of hints, Keith. The contact blocks do not have to be shown in the drawing adjacent to each other. In the case of interlocked pushbuttons for a reversing starter or a two speed starter, the normally closed section of the switch can be shown in a different line and offset to one side or the other. The sections are joined by a dotted line. For selector switches with a lot of contacts, the contacts can be shown in seperate locations, threaded together with a dotted line. It is considered good form to keep the switch sections as close together as is consistent with the circuit. You can usually arrange your diagram to keep your dotted lines reasonably short and limit as much as possible lateral shifts in location.
For selector switches with a lot of contacts, a "Truth table" is often shown to indicate the connections in each position.

The convention suggested by electricpete is also familiar to me but it is a different device. The magnetic motor starters supplied for the HVAC industry used to commonly have a light duty "Hand-Off-Auto" switch mounted in the cover. The physical arrangement of the switch and the symbol are just as shown by electricpete.

I haven't used it for awhile, but I still have the old template with all those symbols on it.

The symbols you have, Keith, work quite well with horizontal ladder type schematic diagrams. Drawing in the jumpers is valuable as it leaves no ambiguity for either the panel assembler or the service technician.

I understand your dislike for a different standard from what you're used to. I feel the same way when I run up against something like a Carrier Container Unit and try to figurew out a control sequence from a schematic in an unfamiliar format.
Those symbols that you dislike used to be and probably still are CEMA standards for Industrial Control Systems. (CEMA is the Canadian eqivalent of NEMA and I understand is almost identical)
Respectfully

 

[Skogsgurra]

I find the original symbol quite clear and it also doesn't contain much (any) redundant information. The dashed lines tell which switching element is activated in the two actuator positions. The crosses are used so that the lines can be drawn to more distant elements without falsely indicating non-active elements it happens to pass on its way.

It is a good symbol. You better get used to it - and use it - if you want to have a good relation to the people in that particular branch of industry. I once tried a simplified and "better" way of drawing hydraulic symbols, more in the electronic diagram style. I ended up redrawing the whole thing to get my last 10 percent pay.

Gunnar Englund

http://www.gke.org

 

[electricpete]

One more quick comment about the table method:
On slide 2 above you'll note
HS-0002 switch 1 is labeled "Auto/Open"
HS-0002 switch 2 is labeled "Closed"
HS-0002 switch 3 is labeled "Auto/Closed"
HS-0002 switch 4 is labeled "Open"

These labels tell you what switch positions cause the contact to close without even looking at the table.

I suspect that won't change your approach but I just wanted to mention it.

As far as original symbol I wasn't sure if that is pushbutton or rotary but the description "spring return to center" made it clear it was rotary. Out of curiosity waross, how do you get 3 positions on a pushbutton?

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[waross]

Hi electricpete;

Out of curiosity waross, how do you get 3 positions on a pushbutton?

In my GE Control catalogue, 1995 issue, the convention is used for both the wiring diagrams of the motor starters and to describe the action of the various push buttons and selector switches.

The standard drawing convention is used for both bush buttons and selector switches, two position selector switches and three position selector switches.
I spent some time looking online for a good example of a diagram using the symbols but so far no luck.
I'll post something if I find it.
respectfully

 

[itsmoked]

Maybe I'll stick with the original,(yuck) because as poor as I think it is I do see the logic with sticking with a standard or at least the "local standard".

Thanks for your efforts electricpete I actually think your:
Hand_Off_Auto
1-2__X___________
3-4____________X_
With note nearby "Spring return to Off"

has a lot going for it, especially with respect to my switches that have three times the contacts.. hmmmm I may still go that way instead.

This seems pretty clear to me a tabular/symbolic hybrid. scematics

----> <----
Off Auto Hand
___1 X 2___
___3 X 4___
___5 X 6___
___7 X 8___
___9 X 10__
__11 X 12__

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi Keith and Pete
I found the standards.

http://nema.org/stds/ics19.cfm#download

You may have to go to nema.org and log on.
I did a search on the site for control symbols and the download in question came up 1st on the list.

Free Standard: ICS 19-2002
Industrial Control and Systems: Diagrams, Device Designations, and Symbols

respectfully

 

[jraef]

I have to chime in with the conventional wisdom on this as well Keith. Like it or not, that is the JIC symbol that electricians learn to recognize and understand. To make up something new is to risk someone not recognizing your intent at some future date. It can be a bit cumbersome on muti-function switches to be sure, and 4 position switches are a real challenge, but it is the way it is.

I worked for a while for e German company who made switches (Moeller) and as most German Co.s do, they had a very organized and systematic way of indicating contact operations using a target chart similar to the one electricpete showed. After they "deprogrammed" me away from JIC symbology I actually liked their method, it made a lot more sense. Moeller cam switch link

Unfortunately not one US electrician understood it, nor did they want to take the time to try. I had to issue supplemental drawings with that standard JIC symbol on almost every project.

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[itsmoked]

Thanks waross for pointing me to that NEMA doc. It's great. I saw several other symbols I'll need in it too. It does have essentially the same symbol that's in my original photo above. It also has one like electricpetes.

Boy jraef, that Moeller symbol is certainly an acquired taste.. lolo

Okay guys I'll stick with a NEMA or a very slightly modified one

skogs your warning is haunting me. I don't need no sting-king hold backs....

Thanks one and all.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

Hi Keith
In case you missed it:
The symbol you are using is as you state, two single pole contact blocks mounted on a single operator (Selector switch or push button.) One contact is normally open and the other is normally closed, held open.

There is another variation that is a double throw contact block. The symbol is similar, but only one horizontal line is shown to indicate the movable contact and the dots are shown closer together."

The double throw versian is usually used for H-A-O service.
However, the double throw version is limited to "Same polarity" switching. To comply with this requirement, the double throw version is almost always used with a common connection to one side of the switch block.
When two single throw contact blocks are used as is indicated in your original post, there is no such limitation.
One double throw contact block is cheaper than two single throw contact blocks.
There are different contact arrangements in an assembled selector switch depending on the shape of the cam.
1> A double throw contact block.
2> A normally open and a normally closed single throw contact blocks.
3> Two normally open single throw contact blocks.
4> Not common but possible, two normally closed contact blocks.
Whatever the contact arrangement, show it on the drawing as shown in your original post. The schematic should indicate the operation of the assembled selector switch rather than the operation of actual contact block.
I hope this helps.
Respectfully