Yokogawa YVP110 - Manual (Page 71)

<12. Transducer Block>
12-2
IM 21B04C01-01E
12.2.2 Position-to-flow Rate
Characteristic Conversion
The parameter POSITION_CHAR_TYPE defines
the characteristics between the valve position and
flow rate, and can be set to one the following:
1 = linear
2 = equal percent (50:1)
3 = equal percent (30:1)
4 = quick open (reversal of equal percent 50:1)
5 = Camflex Percen tage
255 = user-defined
Writing the value 255 allows you to define the
desired characteristics by 10 line segments for
evenly divided input levels. The coordinates
(0,0) and (100,100) are fixed; set the values
corresponding to OUT(Output of AO block) = 10%,
20%, 30%..., 80%, 90%. Note that a set value must
be greater than the preceding set value; the output
must increase as the input increases.
This flow rate conversion is applied to the signal in
the backword path as well.
12.2.3 FINAL_VALUE and Range
The parameter FINAL_VALUE contains the valve
position setpoint for valve control, and its value is
always a percent value where 0% is the shut-off
position as is the case for the input signal. High and
low limits for the value of FINAL_VALUE.value can
be set in FINAL_VALUE_RANGE.
12.2.4 Tight-shut and Full-open Actions
The tight-shut action is an action to decrease the
output pressure to a level much lower than the 0%
pressure level for an air-to-open valve (or increase
it to a level much higher than the 0% pressure level
for an air-to-close valve) when FINAL_VALUE.value
is less than FINAL_VALUE_CUTOFF_LO in order
to ensure that the valve is tightly shut off. After the
tight-shut action is activated, when FINAL_VALUE.
value becomes greater than FINAL_VALUE_
CUTOFF_LO by 1% or more, the tight-shut action
will turn off.
Conversely, the full-open action is an action to
increase the output pressure to a level much higher
than the 100% pressure level for an air-to-open
valve (or decrease it to a level much lower than the
100% pressure level for an air-to-close valve) when
FINAL_VALUE.value is larger than FINAL_VALUE_
CUTOFF_HI in order to ensure that the valve is fully
open. After the full-open action is activated, when
FINAL_VALUE.value becomes less than FINAL_
VALUE_CUTOFF_HI by 1% or more, the full-open
action will turn off.
Although the actual output signal level is changed
to a level outside the range during the period when
the tight-shut or full-open action is on, the value of
FINAL_VALUE.value remains as computed and is
not affected by these actions.
12.3 Backward Path
The following describes the signal input from the
device hardware to the transducer block and then
passed to other function blocks.
12.3.1 FINAL_POSITION_VALUE
The parameter FINAL_POSITION_VALUE contains
a percentage value of the valve position sent from
the position sensor where 0% is the shut-off position
as is the case for FINAL_VALUE.value. When one
or more of the following conditions become true, the
data status of FINAL_POSITION_VALUE becomes
Bad, which is notified to the connected AO block
and upstream function blocks:
• Bad - Out of service: The block is in the O/S
mode.
• Bad - Sensor failure: The position sensor has
failed.
• Bad - Device failure: The A/D converter has
failed.
• Bad - Non specific: The deviation exceeds the
limit.
12.3.2 Limit Switches
Limit switches monitor whether the valve position
has reached a specified high or low limit position
and send the high limit switch status to channel 2
and the low limit switch status to channel 3. The
thresholds (settings) for the high and low limit
switches should be set in LIMSW_HI_LIM and
LIMSW_LO_LIM. The switch statuses sent to
channels 2 and 3 mean:
0 = off (inactive)
1 = on (active)
Hysteresis of 1% is applied for both High and Low
limit switch. While the limit switch of high side stays
ON, it turns to OFF again only when the value
of FINAL_POSITION_VALUE becomes smaller
by 1% or less than the value of LIMSW_HI_LIM.
Also, while limit switch of low side stays ON, it
turns to OFF again only when the value of FINAL_
POSITION_VALUE becomes greater by 1 % or
more than the value of LIMSW_LO_LIM.