Experimental Physics and
Industrial Control System

"Pietryla, Tony via Tech-talk" <tech-talk at aps.anl.gov> · Mon, 29 Mar 2021 12:41:03 +0000

Donny,

You could change your calc record to this:

record(calc, "$(KEIT):CalcCurrent")
  {
     field(SCAN, "1 second")
     field(INPA, "$(KEIT):Charge PP")
     field(CALC, "LA-A")
}

This would subtract the new reading from the last reading.

— 
Anthony Pietryla
Principal Controls Engineer
Advanced Photon Source
Argonne National Laboratory

Phone: 630-252-7430
Fax: 630-252-6123

On 3/29/21, 7:33 AM, "Tech-talk on behalf of Donny Domagoj Cosic via Tech-talk" <tech-talk-bounces at aps.anl.gov on behalf of tech-talk at aps.anl.gov> wrote:

    Hi Marty and Mark,

    Thank you for your quick response.
    What Marty suggested makes sense. If the record is processes in INPA, 
    than of course INPB reads the same value from the Charge record. Thank 
    you for pointing that out.
    However, when I corrected this error as you suggested, the result was 
    still always 0. Changing the order of NPP before PP should have solved 
    this problem but it didnt.

    Using Marks suggestion of setting B to A after the calculation 
    ("B-A;B:=A") works as expected and yields the correct result. This 
    solves my problem, but I still dont understand why Marty's suggestion 
    didnt work.

    Thank you,

    ---
    Donny Domagoj Cosic
      Institut Ruđer Bošković, Bijenička cesta 54, 10000 Zagreb, Croatia

    Dana 29.03.2021 13:48, Smith, Martin via Tech-talk je napisao(la):
    > Hi Donny,
    > 
    >  Because the Charge record is Passive scan and is being processed
    > (presumably) only by
    >  the calc record what you are saying makes sense. the calc record
    > processes the charge
    >  record first for link A using a PP link causing it to get a new
    > value, then it gets that new
    > 
    >  value again using link B without processing (NPP) the charge record.
    > 
    >  I think what you really want is this:
    > 
    >  record(calc, "$(KEIT):CalcCurrent")
    >  {
    >  field(SCAN, "1 second")
    >  field(INPA, "$(KEIT):Charge NPP") # Get the current value of Charge
    > 
    >  field(INPB, "$(KEIT):Charge PP") # Process charge record then get the
    > new value
    >  field(CALC, "B-A") # You may need to change this to A-B if you want a
    > positive value assuming the charge is always increasing
    >  }
    > 
    >  You need to get the current value first then process the record to
    > get the new value.
    > 
    >  Marty
    > 
    > -------------------------
    > 
    > FROM: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Donny
    > Domagoj Cosic via Tech-talk <tech-talk at aps.anl.gov>
    >  SENT: Monday, March 29, 2021 6:35 AM
    >  TO: Tech-talk <tech-talk at aps.anl.gov>
    >  SUBJECT: Rate of change calculation
    > 
    > Hello,
    > 
    >  I am trying to calculate the rate of change of a record using a calc
    >  record as follows:
    > 
    >  record(ai, "$(KEIT):Charge")
    >  {
    >  field(DESC, "Measure Charge")
    >  field(DTYP, "steam")
    >  field("@devKeithley6514.proto measureCharge() $(PORT)")
    >  field(SCAN, "Passive")
    >  }
    > 
    >  record(calc, "$(KEIT):CalcCurrent")
    >  {
    >  field(SCAN, "1 second")
    >  field(INPA, "$(KEIT):Charge PP")
    >  field(INPB, "$(KEIT):Charge NPP")
    >  field(CALC, "B-A")
    >  }
    > 
    >  The calc record always returns 0. If I change the calc to B+A, to
    > check
    >  what is going on, I always get double the charge. It seems like the
    > PP
    >  and NPP are both returning the same value even though the actual
    > charge
    >  is changing. Any ideas on why this would be happening or suggestions
    >  would be greatly appreciated.
    > 
    >  Thank you in advance,
    >  Donny
    > 
    >  --
    >  Donny Domagoj Cosic
    >  Institut Ruđer Bošković, Bijenička cesta 54, 10000 Zagreb,
    > Croatia

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System