Rate of temperature rise/drop Siemens block

[kemppioy]

Hello,

Does anyone know if there is a ready made function available in Siemens S7-300 series for rate of temperature rise/drop detection? I need to check a temperature to see if it rises or drops a certain amount within a certain amount of time.

Thanks

PK

 

[RMA]

As far as I'm aware there is no such function, however, I don't see why you would need one. Depending on exactly what you want to do, you're probably looking at between five and ten lines of code called in OB35.

 

[dahnuguy]

Take a variable integer and read it into a table every X time.

Repeat every x time.

Compare the first reading to the second.

If the differ by more than Y amount, turn on an output to indicate the change has exceeded Y in X time.

You can use the stat area of a FB to store the data or you can send the data to DB.

You can also collect 10 or 100 readings in such a DB and still use the first two for your compare. The others would be available to use in other blocks and would create a history of the change.

I used the STAT area of the FB and only keep 3 readings in this example.

 

[dahnuguy]

orrrrrrrrrrr

It might be more usefull to take 10 readings , one every 10sec, and then compare the first to the 10th in my example.

The new data will fill the table and move down FIFO. So every 10 seconds you would be comparing what has happened over the last 100 seconds.

or minutes or hours..........etc.

the more readings you take the better resolution but it takes more memory.

you could also take the variable and move it to a memory location and add the differential number to it.

50 input + 5 diff check hi =55 in M1
50 input - 5 diff check lo =45 in M2

then wait your time period and move the variable into another memory location.

53 input to M3

Compare M3 to M2and M1 and set your alarm bit.

is M3 > M1 or < M2? then set M4.
is M3 < M1 and > M2? then reset M4.

repeat now the new variable level is written to "var input" and the compare goes into the next time period with a new reference.