Experimental Physics and
Industrial Control System

Mark Rivers via Tech-talk <tech-talk at aps.anl.gov> · Mon, 29 Mar 2021 11:52:46 +0000

Hi Donny,

> 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.

I suspect that what is happening is that it first evaluates INPA, processing Charge record.  It then evaluates INPB which reads the Charge record, obtaining the same value that was just read when INPA was evaluated.

I think this will fix the problem.  It just assigns the value of A to B after doing the subtraction.

record(calc, "$(KEIT):CalcCurrent")

{
     field(SCAN, "1 second")
     field(INPA, "$(KEIT):Charge PP")
      field(CALC, "B-A;B:=A")
}

Mark

________________________________
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
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