7
The values of
and
are integers only and are
limited to the range of 1 to 9999. The Model T7900/
T7950 ship from the factory with units of psig, BAR, or
kPa determined by the part number. The Model T7900/
T7950 automatically determines the Output Pressure
Decimal Point location
based on the maximum
Output Pressure
after the N/D conversion.
NOTE:
Unit
N/ /D
Comments
psig
1
1 psig = psig x 1
BAR
100 1451 bar = psig x 0.0689
kPa 6895 1000 kPa = psig x 6.895
InHg
5000 2456 InHg = psig x 2.036
Table 6. Pressure Unit Values
The Setpoint
and Deadband
item
values display in terms of the converted
pressure units defined by the
and
conversion factor.
For more information about
and
values for
common pressure units, see Table 6.
Pressure Unit Conversion (
) and (
) cont.
Configuration Menu
Operation
Control Value used as Setpoint Control (
), (
),
(
) and (
)
The values in
,
,
and
set the relationship
between the control input signal and the output pressure.
Setpoint is displayed in terms of the output units. Config-
uring the control input for setpoint control, (
=
),
allows for the adjustment of the relationship between con-
trol input signal and the output. To make the adjustment,
set the appropriate values in
,
,
and
on the
Configuration
menu. When the control input signal
varies between the values in
and
, the pressure
output varies proportionally between the values in
and
. For example:
= mA,
= 0.00,
= 30.00,
=
4.00, and
= 20.00; Varying the control input
current between 4 mA and 2- mA varies the
pressure setpoint proportionally between 0 and
30 psig.
To achieve a reverse acting relationship, set
= 20.00 and
= 4.00 or set
= 30 and
= 0.
Option Value (
), (
)
Sets the analog value of
and
proportional to
and
, respectively.
= mA,
= 0.00,
= 30.00,
=
4.00, and
= 20.00; The Option Value will
vary between 4 mA and 20 mA proportinally
following the pressure output between 0 and 30
psig.
To achieve a reverse acting relationship, set
= 20.00 and
= 4.00 or set
= 30 and
= 0.
Look Ahead Items
and
Configuring Menu
- Tuning Coefficients
The Model T7900/T7950 ships from the factory with nomi-
nal PID values. Tune the PID coeffecients
,
and
for optimum performance in the Tuning menu
.
There are several PID optimization routines used to adjust
the PID coefficients. The following is a basic procedure
that works in most applications:
1.
Start with
= 1.00,
= 0, and
= 0.
should be set to zero when optimizing PID. Re-
turn
to the required value after optimizing PID.
2.
Increment
by 0.01 or other minimal value.
3.
Change the Setpoint
from 50% full-scale to
70% full-scale. Change the setpoint back to 50%
4.
If the output stabilizes, go back to 1.
5.
If the output does not stabilize, measure the pe-
riod (in seconds) of the oscillations and go to step
6.
6.
Set
to 50% of the final unstable value previ-
ously identified. Set
to the period of the os-
cillations. Set
=
x 1/8.
To improve response characteristics , the Look Ahead
function predicts the required internal control correc-
tion for a specific setpoint based on the characterizing
values
and
.
must be enabled in the Setup
Menu. The Look ahead
function is pressure sup-
ply sensitive requiring the pressure supply be set at the
expected operating value. To set
and
, use the
following steps:
1.
Set the Deadband
on the Tuning
menu to zero.
2.
Set the Setpoint
to a value between 10
and 20 % of the maximum operating range.
3.
Access the Configuration
menu. Scroll
through the menu until
displays. Press
the enter key, select
. When
flashes
on the display, the new value is set.
4.
Repeat the procedure for
with the setpoint
between 70 and 100 % of the operating range
.
Option Value (
), (
) (cont)
