Yokogawa AXFA14G/C - Manual (Page 79)

IM 01E20F02-01E A-20
APPENDIX 3. ARITHMETIC (AR) BLOCK
A3.3 Computation Section
A3.3.1 Computing Equations
This subsection shows computing equations used in the
computation section:
1) Flow compensation (linear)
func = PV
ϫ f
f = (t_1 / t_2)
2) Flow compensation (square root)
func = PV
ϫ f
f = sqrt(t_1 / t_2 / t_3)
3) Flow compensation (approximate expression)
func = PV
ϫ f
f = sqrt(t_1
ϫ t_2 ϫ t_3 ϫ t_3)
4) Quantity of heat calculation
func = PV
ϫ f
f = (t_1 - t_2)
5) Multiplication and division
func = PV
ϫ f
f = ((t_1 / t_2) + t_3)
6) Average calculation
func = (PV + t_1 + t_2 + t_3) / N
where N: number of inputs
7) Summation
func = PV + t_1 + t_2 + t_3
8) Polynomial computation
func = PV + t_1 2 + t_2 3 + t_3 4
9) HTG-level compensation
func = (PV - t_1) / (PV - t_2)
10) Polynomial computation
func = PV + t_1
ϫ PV
2 + t_2
ϫ PV
3 + t_3
ϫ PV
4
* Precaution for computation
Division by “0”: If a value is divided by “0,” the
calculation result is interpreted
as 10
37 and, depending with
core, a plus sign is added to it.
Negative square root: The square root of an absolute
value is extracted and a minus
sign is added to it.
A3.3.2 Compensated Values
In computing equations 1) to 5) in A3.3.1, the value
“f” is restricted by the COMP_HI_LIM or
COMP_LO_LIM parameter. In this case, the value “f”
is treated as follows:
If “f” > COMP_HI_LIM,
f = COMP_HI_LIM
If “f” < COMP_LO_LIM,
f = COMP_LO_LIM
A3.3.3 Average Calculation
In computing equation 6) in A3.3.1, the average of
input value is calculated. Here, it is necessary to obtain
the number of inputs, N. For this, determination is
made to see if the sub-status of each input is “Not
Connected.” Note that the main inputs may be accepted
if IN or IN_LO is not in “Not Connected” sub-status.
In this case, the number of inputs that are not in “Not
Connected” sub-status is regarded as “N.”
A3.4 Output Section
After executing the computing equation, the block
applies a gain to the calculated result and then adds a
bias to it.
It then substitutes the result into PRE_OUT and if the
mode is in AUTO, the value of PRE_OUT is taken as
OUT.
PRE_OUT = func
ϫ gain + bias
where func: result of computing equation execution
OUT = PRE_OUT (when the mode is in AUTO)
Next, the block performs limitation processing
(OUT_HI_LIM, OUT_LOW_LIM). This processing is
described as follows with respect to the value of
PRE_OUT.
If PRE_OUT > OUT_HI_LIM:
PRE_OUT = OUT_HI_LIM
The “high limited” processing is applied
to the status of PRE_OUT.
If PRE_OUT < OUT_LO_LIM:
PRE_OUT = OUT_LO_LIM
The “low limited” processing is applied
to the status of PRE_OUT.