SMAR CD600 Plus - Function 16 - Pressure and Temperature Compensation (Ptc); Operation

Library of Function Blocks
4.43
Function 16 - Pressure And Temperature Compensation (PTC)
Operation
This block can compensate gas flow for pressure and temperature variation, liquid flow for
temperature variation and saturated steam flow for pressure or temperature variation.
The flow transmitter signal shall reach the block input as a linear signal, i.e., should the signal be
from a differential pressure transmitter, the square root must be extracted in the analog input block.
GAS: Q = Q
C
P
T
K
LIQ: Q = Q
C
BLK 063/064
A
B
C
D
79/80
p
QL
QH
t
It is possible to have higher rangeability measurement, by using signals from two transmitters
calibrated in different ranges. For this reason, the block has a parameter (
ALL) which determines
the percentage of the range corresponding to the highest value of the lower range.
rate Flow Maximum
100% =
Q
L
to ingcorrespond Flow
= ALL
The lower range transmitter shall be connected to the input C and the higher range transmitter shall
be connected to input
D.
When
Q
H
>ALL Q = Q
H
If
Q
H
≤ALL Q = Q
L
. ALL
1
00
Input values may vary between -102.00 and +102.00%. Output may go from -2 to +102%.
FORMULA FOR GASES
CBTAP
K
T
P
QQ
C
++
= .
Where,
Q
c
- Compensated flow rate
Q - Noncompensated flow rate
P - Absolute pressure in engineering units
T - Absolute temperature in engineering units
A, B and C - Coefficients which express the gas compressibility factor (Z). For ideal gases, A = B = 0
and
C =1.
K - Constant which defines the project conditions of the flow primary element. K is calculated as
follows:
) C +
BT
+
AP
( .
P
T
= K
PP
P
P