Electronic Schematic / Diagram devices 1

[jphavener]

I have a customer that continues to comment that I need to be showing my devices in the "alarmed" state on my control panel schematic. I have always understood that on schematics, devices were shown in the powered off / shelf state. Is there a standard / recommended practice / publication that defines this or is it just an understood thing?

Thanks,
Jeff

 

[dpc]

It is customary to show in off-the-shelf state. I generally always include a description of the contact operation also.

David Castor

http://www.cvoes.com

 

[VEBill]

His request might be self-contradictory if you have (for example) WATER LEVEL TOO HIGH and WATER LEVEL TOO LOW, signals that should never both be in the "alarm" state at the same time.

Then again, it's a good exercise to consider such failure modes anyway.

Would the customer be happy if you provided a set of signal flow diagrams for the alarm conditions? Or are there too many to contemplate doing that?

 

[xnuke]

IEEE Std 315 Graphic Symbols for Electrical and Electronics Diagrams has this in Section 4.3:

The standard method of showing a contact is by a symbol indicating the circuit condition it produces when the actuating device is in the deenergized or nonoperated position. The actuating device may be of a mechanical, electrical, or other nature, and a clarifying note may be necessary with the symbol to explain the proper point at which the contact functions; for example, the point where a contact closes or opens as a function of changing pressure, level, flow, voltage, current, etc. In cases where it is desirable to show contacts in the energized or operated condition and where confusion may result, a clarifying note shall be added to the drawing.

xnuke
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[jraef]

If every technician and electrician is trained to view schematics with contacts shown in the de-energized state (as they are) and your drawings show them in something else, then you are just asking for trouble in the field.

By the way, what is an "alarm state" anyway? it's not that I can't ASS-u-me what it is, the point I am making is that as it is not an industry standard term, someone else may interpret that slightly differently, hence more risk for errors. That's why we have standards such as IEEE, IEC, NEMA/JIC, ANSI etc.


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[stevenal]

Power off, springs discharged, liquid levels low, pressures at atmospheric.

 

[jphavener]

Thank you all for the responses. You have confirmed that I know a little bit of what I am talking about anyway. Xnuke, thanks for the excerpt of IEEE 315.

I think that my customer may not exactly understand that they are only looking at a wiring schematic and not a trip logic diagram or alarm and trip diagram or anything else along those lines.

Thanks again,

Jeff

 

[minder]

Wouldn't a slight variation to the 'off the shelf' condition be a N.C. limit switch held open symbol, or N.O. held closed symbol?
Normally closed, and N.O. HELD closed are different symbols, and is still used as per the old JIC standard for device designation.
M.

 

[jphavener]

In the instance of the held open/closed switches I always note that under the switch. I always set them in the fail position of the valve. Not sure if that is typical or called out in a standard anywhere.

Jeff

 

[minder]

The way I interpret the JIC description of a N.O or N.C. switch Held Closed or open, is that the circuit that operates on the switch is de-activated, power off condition?
M.