Deviation Alarm

[strebej]

OK guy's and gal's
I need help with this one. I have 2 oxygen sensors. I need to set up an alarm if the signal between the two senors deviate more than 5%. I'm using a Siemens 315-2DP using Simatic S7 Software to program it with. I have a first out alarm programmed. I need help with choosing the right comparator block or blocks that will set an alarm bit that I can use in my alarm program.

Jim

 

[Willy Maas]

Alarm comparator

Hi Strebej,

I've used exactly what you need, the code is as following:

L DBW 2 // Value 1
L DBW 8 // Value 2
-I //Subtract
SPP Pos //If diff. positive, don't invert.
INVI //otherwise invert
Pos: L DBW 10 // max allowable Diff.
>=I
= M187.6 // Diff. > max. allowable Diff.

The inverting part is needed when value 2 > value 1.

I am using the german programming package so the actual syntax might be different in the english version.

In my program i have a fixed value in DBW10, but You could also calculate 5% of your setpoint and transfer it into DBW10.

Hope this will work for you.

 

[strebej]

Thank you for your help but I still don't understand?.. Could you please show me this progam in Ladder Logic? I don't know how to program in "STL"

 

[DesertDog]

Range

Here is a ladder of a block I use to turn the output of the block on if the value is within the upper and lower limits, otherwise off.

You can import this source code (AWL) if you want.

FUNCTION "Range_Real" : VOID

TITLE =Range_Real

VERSION : 0.0



VAR_INPUT

  LowerLimit : REAL ; 

  UpperLimit : REAL ; 

  PV : REAL ; 

END_VAR

BEGIN

NETWORK

TITLE =Find If PV Is Between Upper & Lower Values

      A(    ; 

      L     #PV; 

      L     #LowerLimit; 

      >=R   ; 

      )     ; 

      A(    ; 

      L     #PV; 

      L     #UpperLimit; 

      <=R   ; 

      )     ; 

      SAVE  ; 

      BEC   ; 

END_FUNCTION

 

[rsdoran]

Take value 1 and determine what 5% is equal too and place in a word file(1). Subtract value 2 from value 1 and place in another word(2), then compare the 2 words...ie if word 2 is greater than word 1 then set alarm.

This is a generic explanation but should be simple to implement.

 

[Willy Maas]

Deviation alarm

Hi Strebej,

Below is the code for my solution in LAD.

Have fun.

 

[leitmotif]

Ive been pondering this for a while.

The first question is what is the process where you need redundant oxygen detectors?? Mostly curiosity and learning opportunity.

The other thought I have is what if both stray say 10% hi or low. They are within 5% of each other BUT erroneous.

Seems to me to set a tolerance of 2.5% (plus or minus) on each one.
IF they are that accurate
That way you get an alarm if one strays out of spec hi and one strays out of spec low with max difference of 5%.

Dan Bentler

 

[djbillyd007]

When u encounter the stl version you can enter it a written and then switch to ladder view to get an idea