Help Please

cobbrobinson · Mar 25, 2021

I have 7 inputs from sensors and I want to turn on an audible alarm if 2 or more are triggered. Is there a way to do this without writing all the logic out in a huge rung? I know there should be but I'm drawing a blank.
Thanks in advance.

Ryan

Jim3846 · Mar 25, 2021

do a compare the IO card to the states where the inputs are in a clear state. save the clear state register values. compare the clear state register with the Io card register. If not equal sound alarm horn.

cobbrobinson · Mar 25, 2021

That will alarm if just one input is active if I'm following you correct. For my process I would like to only alarm if 2 or more are active.

Ken Moore · Mar 25, 2021

If Input is True use a rising edge to add 1 to a holding register. Do this for all inputs. Then if register is >1 set alarm. Else move zero to register.

tragically1969 · Mar 25, 2021

talking rubbish, ignore

JLand · Mar 25, 2021

CLR(AlarmIndex)
XIC(input0)---ADD(1, AlarmIndex, AlarmIndex)
XIC(input1)---ADD(1, AlarmIndex, AlarmIndex)
.
.
.
XIC(input6)---ADD(1, AlarmIndex, AlarmIndex)

GEQ(AlarmIndex, 2)---OTE(Horn)

Basically, every scan clear out a tag that keeps track of the number of currently active alarms (AlarmIndex), and add to that tag 1 for every alarm that is active. Set a horn bit high if the tag is greater than or equal to 2.

If the inputs are members of an array, you could condense the code with an FSC, but in my opinion that is a bit overkill and unnecessarily complex for only 7 inputs.

Additionally, you could do an OTL instead of OTE for the horn or tie it into existing alarming as appropriate. If you OTL, just be sure to clear the bit on the first scan.

This is just a more verbose description of Ken's method.

drbitboy · Mar 25, 2021

If OP can copy the alarm bits into an integer,
AND
if that integer is big enough to hold all your alarms,
AND
if that integer result is non-zero,
AND
if that integer does not have exactly one bit set,

then there must be two or more active alarms.

I assume OP knows how to do, or test for, (1), (3) and (5); they can ask The Google how to do (7) (it was also answered in this forum a several months ago).

This would only work for the "two or more" case, of course.

cobbrobinson · Mar 25, 2021

JLand said:
CLR(AlarmIndex)
XIC(input0)---ADD(1, AlarmIndex, AlarmIndex)
XIC(input1)---ADD(1, AlarmIndex, AlarmIndex)
.
.
.
XIC(input6)---ADD(1, AlarmIndex, AlarmIndex)

GEQ(AlarmIndex, 2)---OTE(Horn)

Basically, every scan clear out a tag that keeps track of the number of currently active alarms (AlarmIndex), and add to that tag 1 for every alarm that is active. Set a horn bit high if the tag is greater than or equal to 2.

If the inputs are members of an array, you could condense the code with an FSC, but in my opinion that is a bit overkill and unnecessarily complex for only 7 inputs.

Additionally, you could do an OTL instead of OTE for the horn or tie it into existing alarming as appropriate. If you OTL, just be sure to clear the bit on the first scan.

This is just a more verbose description of Ken's method.

Ken Moore said:
If Input is True use a rising edge to add 1 to a holding register. Do this for all inputs. Then if register is >1 set alarm. Else move zero to register.

Thanks gentlemen. This worked great.

daba · Mar 26, 2021

If I remember correctly, there was a "bit-hack" posted for this a while back, but it did assume all of the bits were in one integer.

Anyway the OP has got it working, so not bothering to search for it, bit the "bit-hack" method would be of benefit to others facing the same problem.

drbitboy · Mar 26, 2021

daba said:
If I remember correctly, there was a "bit-hack" posted for this a while back, but it did assume all of the bits were in one integer.

Anyway the OP has got it working, so not bothering to search for it, bit the "bit-hack" method would be of benefit to others facing the same problem.

see post #7.

Mickey · Mar 27, 2021

daba said:
If I remember correctly, there was a "bit-hack" posted for this a while back, but it did assume all of the bits were in one integer.

Anyway the OP has got it working, so not bothering to search for it, bit the "bit-hack" method would be of benefit to others facing the same problem.

http://www.plctalk.net/qanda/showthread.php?t=89560&highlight=bit-hack

daba · Mar 27, 2021

Mickey said:
http://www.plctalk.net/qanda/showthread.php?t=89560&highlight=bit-hack

Thanks Mickey, my memory not so good these days ....

PreLC · Mar 28, 2021

Made some ladder, this should work too, in one rung:

Works for 32 bits, but I'm sure for longer boolean arrays we can write an AND and SUB AOI which can handle even more alarms.

parky · Mar 28, 2021

Dump AB/CLX buy Mitsubishi they have a function that does just that, nice & simple.

daba · Mar 28, 2021

parky said:
Dump AB/CLX buy Mitsubishi they have a function that does just that, nice & simple.

Just make it an AOI, then AB will have that function ....

Help Please

cobbrobinson

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Jim3846

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cobbrobinson

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Ken Moore

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tragically1969

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JLand

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drbitboy

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daba

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Mickey

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PreLC

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parky

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daba

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