ABB US/U 4.2 in counter mode

[Warichet]

Hello,

I'm using an ABB US/U 4.2 configured in counter mode with the différentiel counter enabled.

There is a minor annoince that puzzles me; the flag "differential counter overflow"
Once this flag has been set, it STAYS set ! Bizarre, no ?
In a classical CPU, which I used to know and love, the flags reflects the status of the last operation.
If the next operation doesn't generate an "overflow", well, this
flag is supposed to be reset by the CPU, no ?
NB: the "reset diff ctr" function has no influence on the flag, confirmd by the monitor.
The de re-programming of the device does reset the flag. So, in normal working conditions, this flag, once ON, stays ON ad vitam.....
I'm questionning the usefullness of this thing, unless I'm totally wrong in my reasonning.

[Gaston]

Hi Raymond,

Resetting the overflow to 0 will have no sense as you may never have the chance to read it. With the external signal running at a few Herz you will have a very small chance to read the value at the correct time.

Thus the overflow is an event, not a state. This means the overflow is send as event to the bus once the overflow occurs.

Cheers,
Gaston

[Warichet]

Hi Gaston,

Nice to hear from you again

Resetting the overflow to 0 will have no sense as you may never have the chance to read it. With the external signal running at a few Herz you will have a very small chance to read the value at the correct time.

Thus the overflow is an event, not a state. This means the overflow is send as event to the bus once the overflow occurs.

Sorry to be a pain, but I still fail to undestand this thing.
I guess, if the designer of the US/U decided to expose the overflow flag, it must be of some use ?
I know, it's quite an academic discussion, but event or state, there must be a way to use it. How could I catch an event with the monitor ?
If you have a practical example, it would shed some light in my darkness

Thank you

[Michel]

The overflow flag will be set to 0 (zero) if you reset the differential counter.
So it could be used e.g. to sent a message in case a Maximumlevel has reached.
Usage: Once the overflow flag is received, send a Value-Read Telegram on the Differential-Counter Value or a "1" to the send values object. After receiving the value send a "1" to the differential-counter-reset object.

[Gaston]

The overflow flag will be set to 0 (zero) if you reset the differential counter.

This is an undocumented behavior, so not guaranteed to happen.

So it could be used e.g. to sent a message in case a Maximumlevel has reached.
Usage: Once the overflow flag is received, send a Value-Read Telegram on the Differential-Counter Value or a "1" to the send values object. After receiving the value send a "1" to the differential-coutner-reset object.

Don't know what this should be good for, but ok. You risk to loose counter impulses on the differential counter then.

As said the overflow is an event as opposed to a value. Event means that a telegram is sent to the bus when the event (here overflow) triggers. A receiver can then react on the telegram. You probably know that in this case its not really an overflow but a threshhold (parameter) passing.

Understand it like a button to dwitch on a light, it will send a "1" whenever it is pushed. It will never send a "0" 8when released) and it may never become 0 even if the light is off.

Its meant to be used to trigger something after a given number of impulses.

Example: Imagine you want to realize an additional secuirity agaiinst water leakage. You get 1 impulse per Liter used. You will then have some logic which resets the differential counter once no water has been used for some time. Thios coud b3e done by sending the counter value repeatedly for examle every minute and some logic comparing it to the previous value, if same, reset differential counter.

Now lets assume you know that you will never use more then 100L in your house, so you set the overflow parameter to 120L. Once now you use more then 120L without break inbetween the overflow will be triggered and allow an actor to react and for example close an electric valve.

Cheers,
Gaston

[Warichet]

Hi Michel,

The overflow flag will be set to 0 (zero) if you reset the differential counter.
So it could be used e.g. to sent a message in case a Maximumlevel has reached.
Usage: Once the overflow flag is received, send a Value-Read Telegram on the Differential-Counter Value or a "1" to the send values object. After receiving the value send a "1" to the differential-counter-reset object.

This is exactly what I expected about the flag behaviour, but I'm unable to make it work.
So, I'll re-do my tests, maybe I made a mistake somewhere.