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34
J D F 3 0 0 | F I E L D I N D I C ATO R | O I/ J D F 3 0 0 - E N R E V. B
The bias can be used to correct for absolute temperature or pressure. The gain can be used to normalize terms within a square root
function. The output also has gain and bias constants for any further adjustment required. The range extension function has a graduated
transfer, controlled by two constants referenced to IN. An internal value, g, is zero for IN less than RANGE_LO. It is one when IN is greater
than RANGE_HI. It is interpolated from zero to one over the range of RANGE_LO to RANGE_HI. The equation for PV follows:
PV = g * IN + (1-g) * IN_LO
If the status of IN_LO is unusable and IN is usable and greater than RANGE_LO, then g should be set to one. If the status of IN is unusable,
and IN_LO is usable and less than RANGE_HI, then g should be set to zero. In each case the PV should have a status of Good until the
condition no longer applies. Otherwise, the status of IN_LO is used for the PV if g is less than 0.5, while IN is used for g greater than or
equal to 0.5. An optional internal hysteresis may be used to calculate the status switching point.
Six constants are used for the three auxiliary inputs. Each has a BIAS_IN_i and a GAIN_IN_i. The output has a BIAS and a GAIN static
constant. For the inputs, the bias is added and the gain is applied to the sum. The result is an internal value called t_i in the function
equations. The equation for each auxiliary input is the following:
t_i = (IN_i + BIAS_IN_i) * GAIN_IN_i
The flow compensation functions have limits on the amount of compensation applied to the PV, to assure
graceful degradation if an auxiliary input is unstable. The internal limited value is f.
Equations
Algorithm Type
Flow Compensation Linear
Flow Compensation Square Root
Flow Compensation Approximate
BTU Flow
Traditional Multiply Divide
Description
Used for density compensation of Volume flow
Usually:
- IN_1 is pressure è (t_1)
- IN_2 is temperature è (t_2)
- IN_3 is the compressibility factor Z è (t_3)
Both IN_1 and IN_2 would be connected to the same
temperature
NOTE:
• The Square Root of the third power can be
achieved connecting the input to IN and IN_1.
• The Square Root of the fifth power can be
achieved connecting the input to IN, IN_1, IN_3.
• IN_1 is the inlet temperature
• IN_2 is the outlet temperature
Function
OUT = ( ƒ * PV * GAIN + BIAS)
_
1
t
Where ƒ =
is limited
t
_
2
OUT = ( ƒ * PV * GAIN + BIAS)
t
_
1
Where ƒ =
for Volumetric Flow is limited
t
_
2
∗
t
_
3
For the calculation of the Volumetric Flow t_3 = Z
The compressibility factor Z can be set writing into
the IN_3 a constant value Z or can be calculated
by a previous block linked in the IN_3.
OUT = ( ƒ * PV * GAIN + BIAS)
t
_
1
∗
t
_
3
Where ƒ =
for Mass Flow is limited
t
_
2
In case it would be necessary produce the Mass
Flow, the compressibility factor Z must be set as
1
into the IN_3 as
Z
OUT = ( ƒ * PV * GAIN + BIAS)
2
t
_
1
∗
t
_
2
∗
t
_
3
Where ƒ =
is limited
OUT = ( ƒ * PV * GAIN + BIAS)
Where ƒ = t_1 – t_2 is limited
OUT = ( ƒ * PV * GAIN + BIAS)
t
_
1
Where ƒ =
+ t_3 is limited
t
_
2
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