Emerson VILTER MicroVission Operation And Service Manual page 179

Section 20 • Auxiliary I/O
Setpoint:
• Setpoint used by PID engine.
I Op. Band:
• This setpoint defines the operational band for accu-
mulation of integral error as per value of I+ (Reset).
Examples:
Case I -
PID Settings
P = 1 Setpoint = 20, I Op. Band = 5
I + (Reset) = 1
I – (Reset) = 1
D = 1 Inverse (20 – 4 mA) = Disabled
In this case, the integral error will get accumulated
when the value of process variable falls within the lower
band as determined by I Op. Band setpoint. (Setpoint – I
Op. Band) <= Process Variable < Setpoint. Hence 15 <=
Process Variable < 20.
Case II -
PID Settings
P = 1 Setpoint = 20, I Op. Band = 5
I + (Reset) = 1
I – (Reset) = 1
D = 1 Inverse (20 – 4 mA) = Disabled
In this case when negative error is enabled, the inte-
gral error will get accumulated when the value of pro-
cess variable falls within the upper band as determined
by I Op. Band setpoint. Setpoint < Process Variable <=
(Setpoint + I Op. Band). Hence 20 < Process Variable <=
25.
Inverse (20 – 4 mA): This option is used to inverse an
Analog Aux Output, to vary its output from 20 mA to 4
mA. Typically used where normally open solenoids are
to be operated.
Examples:
Case I -
PID Settings
P = 1 Setpoint = 20, I Op. Band = 0
I + (Reset) = 1
I – (Reset) = 1
D = 1 Inverse (20 – 4 mA) = Enabled
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Other Settings
Interval = 1 sec
Negative Error = Disabled
Other Settings
Interval = 1 sec
Negative Error = Enabled
Other Settings
Interval = 1 sec
Negative Error = Disabled
In this case, the error calculated by the PID engine will
modulate analog output from 20 mA to 4 mA when pro-
cess variable is below setpoint i.e., 20. Similarly, analog
output will get modulated towards 20 mA when process
variable is above setpoint.
Case II -
PID Settings
P = 1 Setpoint = 20, I Op. Band = 0
I + (Reset) = 1
I – (Reset) = 1
D = 1 Inverse (20 – 4 mA) = Enabled
In this case when negative error is enabled, the error cal-
culated by the PID engine will modulate analog output
from 20 mA to 4 mA when process variable is above set-
point i.e., 20. Similarly, analog output will get modulated
towards 20 mA when process variable is below setpoint.
Negative Error: The negative error option determines
the calculation of error by the PID engine to modulate
the analog output. When negative error option is en-
abled, the error will be calculated as Process Variable mi-
nus Setpoint (Process Variable – Setpoint). Hence when
Process Variable is above Setpoint, PID engine will ramp
up analog output towards 20 mA when Inverse (20–4
mA) option is disabled.
Similarly, if negative error option is disabled, the error
will be calculated as Setpoint minus Process Variable
(Setpoint – Process Variable). Hence when Process
Variable is below Setpoint, PID engine will ramp up ana-
log output towards 20 mA when Inverse (20 – 4 mA) op-
tion is disabled.
Interval: This setpoint defines the time interval for cal-
culation of Integral Error.
Examples:
PID Settings
P = 1 Setpoint = 20, I Op. Band = 0
I + (Reset) = 1
I – (Reset) = 1
D = 1 Inverse (20 – 4 mA) = Disabled
In this case, the integral error will get accumulated or re-
moved at every 10 second time interval.
Other Settings
Interval = 1 sec
Negative Error = Enabled
Other Settings
Interval = 10 sec
Negative Error = Disabled
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