DeltaV AI block scaling

Hi,

I am not exactly figure out scaling in AI block for conventional transmitter. 

I want to know how Field_Val (unit %) is calculated for different L_Type.

My understanding -

1. xD_SCALE low scale value = value for 4mA current and  high scale value = value for 20mA filed current.

2. In Direct scaling,OUT = FIELD_VAL% of OUT_SCALE where OUT_SCALE is copied in xD_SCALE means  (What will be value in FIELD_VAL parameter and how it will be calculated).

3. In indirect scaling, OUT = FIELD_VAL% of OUT_SCALE where FILED_VAL = how much % of filed current is w.r.t. xD_SCALE.

4.In square root scaling and In direct independent scaling ...........................????

Thankyou

Devpriy sahu

• 8 Jan 2018 6:43 AM
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3 Replies

• Matt Stoner

  

  • 8 Jan 2018 12:25 PM

  Have you looked in DeltaV Books Online?

  • It isn't just as simple as the L_TYPE, OUT_SCALE, XD_SCALE as it also depends on how the input is being read from the DST (FIELD_VAL_PCT, FIELD_VAL, HART_FIELD_VAL, etc) to know "how" to set these parameters.
  • In BOL, go to Configuration -> Function Blocks -> I/O Blocks -> Analog Input (AI) function block -> Analog Input function block execution

  Your items listed in 4 are typically used when an orifice is being used for Flow (and a transmitter doesn't already account for this) for Ind Sqr Root and when RTD/Thermocouple inputs are used for Direct Indep (Not Indirect independent).

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• Devpriy sahu

  

  • 8 Jan 2018 1:17 PM

  In reply to Matt Stoner:

  Thanks Matt for your valuable response,I am referring to Book online and block configured for our plant operation,Today i was again trying to understand it and concluded following :-
  (Following are for conventional NON-HART 4-20ma transmitter).
  (OSH = OUT_SCALE_HIGH and OSL = OUT_SCALE_LOW)
  (FILED_VAL_PCT = M% in every case)
  
  1. Block execution flow is
  
  Finding FILED_VAL_PCT (Unit=%) = the % of channel loop current w.r.t 4-20mA current range -------> Calculating FIELD_VAL (Unit = %) ------------> Calculating PV (unit = unit of OUT_SCALE) ---------> Calculating OUT
  
  2. For L_TYPE = Direct scaling
  
  FILED_VAL_PCT (Unit=%) ------------> FIELD_VAL = M% of XD_SCALE (Where XD_SCALE will always be same as OUT_SCALE) --------> PV = FIELD_VAL% of OUT_SCALE --------------> OUT = PV (Considering mode is Auto)
  
  3.For L_TYPE = Indirect scaling
  
  FILED_VAL_PCT (Unit=%) ------------> FIELD_VAL = M% of XD_SCALE --------> PV = FIELD_VAL% of OUT_SCALE --------------> OUT = PV (Considering mode is Auto)
  
  4. For L_Type = Indirect sq.root
  
  FILED_VAL_PCT (Unit=%) ------------> FIELD_VAL = M% of XD_SCALE (Where XD_SCALE will always be same as OUT_SCALE) -------->
  PV = Sqrt( FIELD_VAL% divided by 100) * (OSH-OSL) + OSL --------------> OUT = PV (Considering mode is Auto)
  
  5. For L_TYPE = Direct independent
  Still struggling to understand.
  
  
  My Point is
  
  Is my conclusion in point 1 is right ???????
  
  IS other point 2,3,4 concluded are correct??
  
  
  Matt i am truly thankful to you for sparing out your precious time.

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• Matt Stoner

  

  • 8 Jan 2018 4:09 PM

  In reply to Devpriy sahu:

  Direct L_TYPE means XD_SCALE is not used (OUT_SCALE will be copied to XD_SCALE) and FIELD_VAL would be typically used for when getting a decimal Hart value.
  
  Indirect L_TYPE is scaled in linear fashion, this is typically the 4-20mA use case with DST using FIELD_VAL_PCT, XD_SCALE is 0-100% and OUT_SCALE is the range of the instrument.
  
  Direct Indep L_TYPE means the value isn't scaled at all and XD_SCALE is still used with value plugged into OUT_SCALE. With RTD of range -200 to 1000 °C the XD_SCALE would be set to this range but you probably don't want to display this entire range to operations so the OUT_SCALE is set to the range you wish to see, 0-150 °C for example.
  
  Indirect Sqr Root L_TYPE would have XD_SCALE as the full scale differential pressure of a flow orifice and the OUT_SCALE would be the associated flow rate for that scale. There is a call on here as an example found here: emersonexchange365.com/.../3584

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