Indicator Coloring Scheme

Hi,

I've been reading through IEC 60204-1 and NFPA 79 recently and came across a table about indicator color coding (chapter 10 in both documents). These documents specify meanings for red, yellow/amber, green, blue and "other" colors.

I'm curious as to what (particularly those in the EU) people are actually using for their schemes (primarily from a machine standpoint, not process, for my purposes). What are you using to indicate that the machine is running in automatic (normal) operation? What are you using to indicate the presence of a fault (for example, hydraulic oil overtemperature causing the machine to drop out of automatic)?

I posted this information here before in relation to safety reset pushbutton colours, but it also contains some details on indicator colours according to EN 60204-1...

E-Stop manual reset button

There is also some additional information on the use of flashing frequencies to further enhance an indicator's ability to alert personnel to a particular condition.

To take your examples above -

keshik said:

...What are you using to indicate that the machine is running in automatic (normal) operation? What are you using to indicate the presence of a fault (for example, hydraulic oil overtemperature causing the machine to drop out of automatic)?

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Under EN 60204-1, and as I detailed in that older post, these are the common indicator colours and their meaning -

Table 3: Colours of indicator lights and their meanings relating to the machine status

Colour: RED
Meaning: Emergency situation
Description: Dangerous condition
Operator action: Immediate action to respond to a dangerous condition (e.g. by pressing emergency stop)

Colour: YELLOW
Meaning: Abnormal condition
Description: Abnormal condition; anticipated critical condition
Operator action: Monitoring and/or intervention (e.g. by restoring the intended function)

Colour: GREEN
Meaning: Normal condition
Description: Normal condition
Operator action: Optional

Colour: BLUE
Meaning: Mandatory action
Description: Indication of a condition requiring operator intervention
Operator action: Mandatory action

Colour: WHITE
Meaning: Neutral
Description: Other conditions; may be used if there is uncertainty about the appropriateness of RED, YELLOW, GREEN or BLUE
Operator action: Monitor

To indicate a machine in the normal running condition I would use a GREEN indicator permanently ON. Example: Machine start sequence complete.

To indicate a machine in a general fault condition, or to indicate a specific fault condition, where the fault has stopped the machine, or the Operator is required to stop the machine, or the fault is holding off the machine, I would use a RED indicator permanently ON. Example: Hydraulic oil over-temperature condition.

To indicate an abnormal condition where the Operator's attention is required but the machine may continue to operate, or operation may be resumed, I would use a YELLOW indicator flashing - frequency f1 ratio: 1:1.5. Example: Hydraulic oil low level condition.

Note: for enhancing conditional annunciation, audible alarms can also play a role here, as can HMI terminals.

Example: audible alarm enabled when a machine cycle has been automatically paused and is now about to resume.

Example: a machine's RED general fault indicator has turned permanently ON. The machine's HMI is then referenced for the specific alarm.

Regards,
George

Thanks George. I don't think I've mentioned it before, but I really appreciate the depth that you go into with your posts. You are always a must read for me (and I would expect for many others here as well).

Also, thank you for the link to your previous posts on a similar subject. They go into a lot of detail.

Perhaps a good example of the differences between a yellow/amber and red indicator would be turning the amber light on at a high oil temperature (warning level) and turning on the red at a high-high oil temperature (shut down)?

I've a few more questions that I'm interested in hearing your interpretation of IEC 60404-1 on.

We typically use a six second delay before going into automatic (after all prerequisites have been satisfied). During this time period we pulse an audible horn. At the conclusion of the six second time period the machine enters automatic mode. I don't have a copy of IEC 60073 so I'm going by your comments on page 2 of your above forum link.

1. Six second delay before beginning automatic mode:
- Pulse the audible horn at 0.5 Hz (2.0 seconds on, 2.0 seconds off) [It is interesting that a 1 Hz pulse isn't allowed as that gives nice round one second intervals]
- What would be a reasonable visual indicator? Would flashing the green visual indicator at the same rate as the audible make the most sense? Red (no emergency or fault active), amber/yellow (no abnormal situation active) and blue (mandatory action) don't seem to make sense. That leaves us with green and/or white as our color options. Reading IEC 60204-1 10.3.3 one of the purposes for flashing is "to indicate a change in process (flashing during transition)". This would lead me to be conclude that flashing green would be the appropriate visual indicator during this period.

2. In automatic:
- No audible horn active
- Green visual indicator on steady/permanently.

3. Suspension of automatic:
- This appears to be similar to your first example:

Example: audible alarm enabled when a machine cycle has been automatically paused and is now about to resume.

Click to expand...

It seems that it would make sense to also pulse the green visual indicator as well.

4. Fault condition:
- A situation (high-high oil temperature) occurs that causes the system to drop out of automatic.
- Pulse the audible horn at 2 Hz (0.55 Hz * 4) (0.5 seconds on, 0.5 seconds off)
- Green visual indicator off, red visual indicator on solid.

Does IEC 60073 allow for different intervals for different events? For example, one beep pattern for high oil temperature, a different one for low oil level, and a third pattern for all other events?

I will say that reading standards is an expensive process. Who'd have known that IEC 60073 exists to recommend flashing rates and pulse/pause ratios?

keshik said:

Does IEC 60073 allow for different intervals for different events? For example, one beep pattern for high oil temperature, a different one for low oil level, and a third pattern for all other events?

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I do not know whether or not IEC 60073 allows for it or not, but it seems general consensus is that different flash or beep patterns are not done because they require too much interpretation from the operator. Sounds silly, but try to imagine. You have been trained on an installation 2 years ago. The trainer told you about the different beeps/flashes and their respective meaning and required actions, if any. Now the flashing/beeping occurs. You have to think back: did I hear a fast beep, slow beep? Which different beep signals were there anyway on this system? At the same time you notice smoke coming from that place, is that normal? And a colleague can be heard shouting from another place. It soon becomes overwhelming for the average human brain and you fail to match a meaning to a distinct beep pattern.

Toine said:

I do not know whether or not IEC 60073 allows for it or not, but it seems general consensus is that different flash or beep patterns are not done because they require too much interpretation from the operator. Sounds silly, but try to imagine. You have been trained on an installation 2 years ago. The trainer told you about the different beeps/flashes and their respective meaning and required actions, if any. Now the flashing/beeping occurs. You have to think back: did I hear a fast beep, slow beep? Which different beep signals were there anyway on this system? At the same time you notice smoke coming from that place, is that normal? And a colleague can be heard shouting from another place. It soon becomes overwhelming for the average human brain and you fail to match a meaning to a distinct beep pattern.

Click to expand...

I agree with the difficulty of keeping different beep patterns with different meanings being nearly impossible to keep straight in a pressure situation.

To play the devil's advocate to this, what about if you have multiple cells in close proximity to each other and each has its own audible indicator? Is the correct course of action to look for the corresponding flashing red light when you hear fast beeping (assuming you use only two distinct blink/flash rates: slow and fast with fast being the alert pattern)?

keshik said:

Hi,

I've been reading through IEC 60204-1 and NFPA 79 recently and came across a table about indicator color coding (chapter 10 in both documents). These documents specify meanings for red, yellow/amber, green, blue and "other" colors.

I'm curious as to what (particularly those in the EU) people are actually using for their schemes (primarily from a machine standpoint, not process, for my purposes). What are you using to indicate that the machine is running in automatic (normal) operation? What are you using to indicate the presence of a fault (for example, hydraulic oil overtemperature causing the machine to drop out of automatic)?

Click to expand...

Our DCS group used the move to alarm management as an opportunity to address some of the color issues. We went from symbols with solid fill (green, yellow, red) and a normal running screen looks like a Christmas tree, to color only in the edges of the symbol, and a gray-scale process flow with less bright colors for status, so if the condition is normal (whether running or not) nothing jumps out at you with color. The green, yellow and red are subdued. Our operations people hate any change, so they predictably did not like it. Most of our color status matches what has already been posted.

I agree with our operators in one case. We only blink the outside perimeter of a symbol for a fault so it is harder to pick up on the screen. To make up for that, the alarm banner still shows the high priority issues, and the colors still blink for un-acknowledged, solid for acknowledged but still the highest priority, and disappear when cleared. That does not appear to conform to the IEC guidelines, but we kept that as it was .. at least for now.

We don't change color to indicate AUTO or MANUAL operation of each piece of equipment. It is done as a separate device. A loop for analog control (open valve to control level) and a group start for digital control (run a magnet back and forth every hour to empty scrap iron pulled out of the ore). The Loop or Group Start has the green for running, Red for stopped. The operator needs to know his areas. If he does not know what pieces are involved in the Auto control, he/she really should not be running the place. It is part of the help screens on each page, and part of the training that is done with new operators when they start in the control room.

We've gone away from animating motion of product to make it look like a cartoon, and coloring loops to show what is involved with each automated area. Operators do this all day, every day. They have it memorized. When they come back after holidays, a glance through the help screen for a page is enough to refresh.