Flashing a light

David Garaudy

Member
Join Date
Sep 2003
Posts
1
I would like to flash a light. When a device is in alarm I need to flash a light. I need to keep it simple.

Thanks,
David Garaudy
 
Simple

Many different ways to do it. Here's one:


LT_OFF LT_ON
---|/|------------(TON)


LT_ON LT_OFF
---| |------------(TON)


ALARM LT_ON LIGHT
---| |-----| |-----( )



The key is to seperate the ACTIVATION of the light by the alarm, and the ON-OFF BEHAVIOR of the light

That is, it is the light that goes on-off, not the alarm.
 
alarm light

With the AB PLC you can use a time base bit between the alarm bit and the light output, so when the alarm bit goes true the output will flash at whatever you set the time base scale at.
 
alarm light signal

Something I left out was that you could branch around the alarm bit and put not the alarm bit instruction in it so that the light will stay on, it helps let you know when the bulb is burnt out. So when the alarm is on the light will flash at the rate your time base is set for, and stay solid (continuously) when no alarm is set.
 
alarm light signal

Something I left out was that you could branch around the alarm bit and the time base bit and put not the alarm bit instruction in it so that the light will stay on, it helps let you know when the bulb is burnt out. So when the alarm is on the light will flash at the rate your time base is set for, and stay solid (continuously) when no alarm is set.
 
system clock

David
the simplest way to make a light flashing is to use a system clock bit anded with the alarm activation input to energize the lamp output

Alarm SYS_clock Lamp
---| |----------| |---------------( )

thanks
 
No the simplest way to do this is to buy a flashing light..EXAMPLE:Product Catalog-Federal Signal

Just turn on an output when an alarm exists thats connected to the light, use a PB or HMI to offer a reset. There are other brands available and may offer stackable lights in case you need a multitude of colors to show different things.
 
flashing light

If you choose a Mitsubushi processor you can just use the ALT command this will alternate light on and off untill alarm is cleared. I am sure there are other processors that support such commands.

X0
---------| |---------------------------------{ALT Y0}------


X0 IS ALARM
{ALT YO} IS A Application istruction.
When X0 is made the light will flash, you may also be able to pulse a buzzer as well. You can add a duration circuit if you want to lengthen pulses.
 
monkworm said:
this will alternate light on and off untill alarm is cleared
If David uses the ALT instruction as you suggested, that lamp will flash quite fast! At a frequency of 1/2 the current scan time! I hope he isn't using a relay output! (buzzzz)

The ALT instruction comes in really handy for flip-flops, but I don't see an advantage to use it to flash a lamp... :unsure:

For others, here's Mitsubishi's definition of the ALT instruction:

"The status of the destination device is alternated on every operation of the ALT instruction. This means the status of each bit device will flip-flop between ON and OFF. This will occur on every program scan unless a pulse modifier or a program interlock is used"

Instead of extending it with a timer, why not just use a clock bit as hesham suggested? Mitsubishi's M8013 is a nice 1 second clock.

I guess it all depends on the application... :confused:

beerchug

-Eric
 
A way that I flash a light when I want to flash it at different intervals is to set up a timer and then use limits tests to flash it.

This example uses a timer set to 2 seconds.
B3:0/0 & 1 = Alarm Conditions

XIC B3:0/0 LIM 0 T4:4.ACC 50 > OTE O:0.0/1 (Light)
XIC B3:0/1 LIM 0 T4:4.ACC 150 |
 
Some PLCs have limited number of timers
(like FX from Mitsubishi). Sure you can always
resort to system clock but if you need to adjust
the speed, it's better to have own clock
(although this example uses hardcoded value)
Here is what I do when using single timer:
 

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