Yokogawa EJX930A - Manual (Page 115)

<Appendix 4. Arithmetic (AR) Block>
A4-4
IM 01C25T02-01E
A4.3 Computation Section
A4.3.1 Computing Equations
This subsection shows computing equations used
in the computation section:
1) Flow compensation (linear)
func = PV × f
f = (t_1 / t_2)
2) Flow compensation (square root)
func = PV × f
f = sqrt(t_1 / t_2 / t_3)
3) Flow compensation (approximate expression)
func = PV × f
f = sqrt(t_1 × t_2 × t_3 × t_3)
4) Quantity of heat calculation
func = PV × f
f = (t_1 - t_2)
5) Multiplication and division
func = PV × 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 + GAIN_IN_1 × PV 2 + GAIN_IN_2 ×
PV 3 + GAIN_IN_3 × 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.
A4.3.2 Compensated Values
In computing equations 1) to 5) in A4.3.1, 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
A4.3.3 Average Calculation
In computing equation 6) in A4.3.1, 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.”
A4.4 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 × 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.