Red Lion PCU - Manual (Page 44)

Square Root Linearization (root) (Cont’d)
As a result of the scaling and square root linearization, the following
represents the readings at various inputs:
Delta P
(PSI)
Transmitter
(mA)
Flow
(ft 3 / hr)
0.00 4.00 0
15.63 4.50 1099
31.25 5.00 1554
62.50 6.00 2198
125.00 8.00 3108
187.50 10.00 3807
250.00 12.00 4396
312.50 14.00 4914
375.00 16.00 5383
437.50 18.00 5815
500.00 20.00 6216
Decimal Point Position (dPt2)
For Remote Setpoint operation, the decimal point position is normally
programmed to be the same as the main input. For Internal Cascade operation,
the decimal point may be different from the main input.
Example:
If main input = 500 degrees FS, Second Input = 15.00 PSI FS, then dCPt = 0
and dPt2 = 0.00.
Second Analog Input Scaling Points (dSP1, INP1, dSP2, INP2)
Prior to installing and operating the indicator, it may be necessary to
change the scaling to suit the display units particular to the application.
The indicator is unique in that two different scaling methods are available.
The operator may choose the method that yields the easier or more accurate
calibration. The two scaling procedures are similar in that the operator keys in
the display values and either keys in or applies a signal value that corresponds
to those display value points. The location of the scaling points should be near
the process end limits, for the best possible accuracy.
Once these values are programmed, the indicator calculates the slope and
intercept of the signal/display graph automatically. No span/zero interaction
occurs, making scaling a one-pass exercise.
B e f o r e p r o g r a m m i n g t h e i n d i c a t o r , o r g a n i z e a l l t h e d a t a f o r t h e
programming steps to avoid confusion.
To scale the indicator, two signal values and two display values that
correspond to the signal values must be known. These four values are used to
complete the scaling operation. An example is listed below.
Example:
Scaling Point #1 Scaling Point #2
0.0% @ 4.00 mA AND 100.0% @20.00 mA
Display Values (dSP1 & dSP2)
Key-in the display value for Scaling Point 1 and Scaling Point 2.
dSP1 -999 to 9999 (Ex. 0.0%)
dSP2 -999 to 9999 (Ex. 100.0%)
Signal Input Values (INP1 & INP2)
The signal input value can either be keyed via the front panel buttons or an
input signal can be applied to the appropriate signal input terminals. Initially,
the unit is in the key-in mode.
Key-in Method
Key-in the signal value for Scaling Point 1 and Scaling Point 2.
INP1 -999 to 9999 (Ex. 4.00 mA DC)
INP2 -999 to 9999 (Ex. 20.00 mA DC)
Signal Input Method
To change to the signal input method press the DSP button. Front panel
annunciators %PW and SEC flash and the display indicates the signal value
applied to the input terminals. The unit can be toggled to the key-in method by
pressing the DSP button again.
When the desired value is indicated on the display, press the PAR button to
store the value and advance to the next parameter.
The scaling of the Remote Setpoint and Internal Cascade units are
normally made equal to the physical range of the system.
Example: If the control range of the process is 100 to 400 units, the Remote
Setpoint is normally scaled to 100 and 400.
Example: The Secondary variable under internal cascade control is steam
pressure over the range of 0.00 to 60.00 PSI. The Second Analog input is
normally scaled to 0.00 and 60.00 units.
-36-