Title: Control Using Wireless Throttling Valves
1Chapter 6
- Control Using Wireless Throttling Valves
2Future Vision WirelessHART Throttling Valves in
Closed Loop Control
- Based on the broad acceptance of wireless
transmitters, manufacturers have developed and
introduced wireless actuators for on/off valves.
These devices are being used to implement closed
loop discrete control . - In the future, it is envisioned that
manufacturers will introduce wireless throttling
valves that may be used with a wireless
transmitter to implement closed loop control.
3PIDPlus for Control with Wireless Transmitter
and Valve
- The PIDPlus features may be combined with the
modifications for control using a wireless valve
to address these different combinations of wired
and wireless field devices. - The changes in the PIDPlus for use with a
wireless valve and wireless transmitter are
illustrated. - The use of the implied or actual response
indication as the input to a positive feedback
filter enables the reset contribution to
automatically compensate for delays in the
positioner response
4PIDPlus Structured to Minimize Changes in Target
Valve Position
- The PID may be modified to minimize the number of
changes made in the target valve position when
control is implemented using a wireless valve and
a wireless transmitter. - To minimize the power consumed by the valve
positioner, calculated PID output is transmitted
to the wireless valve only if the criteria
determined by non-periodic control communications
have been met. - The PID is typically scheduled to execute much
faster than the minimum period at which the
target valve position may be communicated to
the wireless valve.
5Wireless Communication to the Valve
- The key to applying non-periodic control
communications is understanding that the PID
reset calculation is implemented using a positive
feedback network based on the implied valve
position, which is communicated to the PID with
minimal delay as the feedback in response to a
change in the target position. - Ideally, this feedback of implied valve position
(i.e., the target position that the valve
accepted and is working to achieve) would be
communicated by the wireless valve back to the
wireless gateway in the response to the target
position write request.
6Example Control Implementation Using Wireless
Valve
- A new WirelessHART command has been proposed that
supports the inclusion of a time to apply field
with the output value communicated to a wireless
valve. - This added field specifies a time in the future
when the output value takes effect. The time to
apply value is selected to ensure that the valve
receives the output communication before this
future time. - Thus, it is possible to calculate the implied
valve position based on the target position
communicated to the valve and the specified time
when the valve takes action on the new target
position.
7- The command sent to the valve will contain the
new target value and the time that the valve is
to act on the new target position. - This time value will be based on the time at
which the new target value was accepted plus the
delay time configured by the user or set by the
manufacturer. - The sequence in which the AO output is processed,
communicated to the valve and then acted on by
the valve is shown in this example
8Control Structure Used in Field Trial
- Field trails were conducted to evaluate a
wireless positioner for a throttling valve - In these field trails the functionality
associated with determining the target to
minimize valve movement and calculation of the
external reset input used in the PID was done in
the control module.
9Test Module Control Using a Wireless Valve
- As part of the applied research into control
using a wireless valve positioner that was
conducted by Emerson Process Management in the
spring of 2014, a module was created that
allows control using a wireless valve to be
tested in a simulation environment. - Composites within the module are used to simulate
the Controller Output Processing (using the new
HART command), the communications and delay
associated with the wireless gateway, and the
wireless valve. In addition, a composite is
provided to simulate the dynamic process.
10- In the first two tests, the control performance
was evaluated using a wired transmitter and a
wireless valve vs a wired transmitter and a wired
valve. Identical changes in setpoint and
unmeasured disturbances were introduced into both
control loops during the tests. - In the first test, the wireless valve
communication to the valve was set to 3 seconds
and the delay in the PID seeing the valve
response was set to 3 seconds in the simulation
of wireless communication. - In the second test, the delay to the valve and
the valve response were set in the simulation to
6 seconds.
11Performance Using a Wireless Valve with a Wired
Transmitter
- During the test, statistics on the number of
communications, valve movement and IAE were
captured in the module by the PERFORMANCE
composite. - Stable control was observed for changes in
setpoint and load disturbances using the wireless
valve. Through the use of valve minimization the
number of changes in valve target was reduced by
a factor of 23.
12PID Control Using Wired Valve and Transmitter vs
Wireless Valve and Transmitter
- The tests were repeated using a wireless
transmitter with the wireless valve. - The transmitter used window communications mode
where the period was 6 seconds, default report
time was 12 seconds and deadband in reporting was
3.
13Performance Using a Wireless Valve with a
Wireless Transmitter
- The results achieved for wireless control using
PIDPlus with the modifications for the wireless
transmitter and valve vs a wired transmitter and
valve using PID are summarized in this table. - Stable control was observed for changes in
setpoint and load disturbances using the wireless
transmitter and valve. Through the use of
minimization of valve movement, the number of
changes in valve target was reduced by a factor
of 23.
14Flow Lab Where Wireless Control Was Tested
- A prototype wireless valve was tested in one of
Fisher Controls flow labs located in
Marshalltown, Iowa using a DeltaV control system
and its embedded PIDPlus algorithm. - In these tests, closed loop flow control was
evaluated using both wireless and wired flow
measurement. - Communications with the wireless valve used a new
HART command that allows a time to apply to be
specified. - The PIDPlus external reset input was modified to
allow delay to be used optionally to compensate
for the time to apply. In addition, a new
technique for minimizing valve movement was
evaluated using a wired and wireless input to the
valve.
15Field Trial Summary
- The test results can be summarized as follows
- PID tuning was set strictly based on the process
gain and dynamics. The fact that the tuning was
never changed throughout the wireless test
illustrates that the PIDPlus tuning is not
impacted by transmitter and valve update rate and
delay introduced by communications. Good control
was achieved in all wireless valve and wireless
transmitter tests using this tuning. - Using a wired transmitter and valve and then
applying valve minimization reduced the number of
changes in valve position by a factor of 70 for
0.1 second loop execution and cut total valve
travel by over 50. Introduction of valve
minimization had no impact on loop stability and
had minimal impact on control performance less
than 50 increase in IAE. - The wireless transmitter update rate was set to 8
seconds for most of the tests and introduced 410
seconds variable delay in the flow measurement
used in control. However, this had no impact on
the stability of PIDPlus control and had minimal
impact on control performance - When a wireless transmitter was used with
PIDPlus, the number of changes in valve position
was reduced by a factor of 47 since the output of
the PIDPlus only changes when a new measurement
is received or the setpoint is changed. - Changing the wireless transmitter update rate
from 8 seconds to 16 seconds had minimal impact
on control performance increasing IAE
approximately 60 for setpoint changes.
16Field Test of Wireless Control
17Control Module for Wireless Field Trial
- Modules created for the field test allow the
selection of a wireless valve and/or wireless
transmitter in a test run and the selection of a
modified DeltaV wireless interface to the
Rosemount 1420 or the standard output cards to be
used in control. - The apply delay may be optionally selected to
compensate for the delay in the time the target
valve position is acted on when control uses
wireless communication to the device.
18Time to Apply Arrival During Test
- The time to apply was set to 8 seconds in all
wireless valve tests. The chart in Figure 6-15
shows a log of normalized Time to Apply as
published by the modified 4320 over the course of
testing. - It shows when the command was received by the
device in relation to when the new setpoint would
be applied via the Time to Apply variable. - Most commands were received before the Time to
Apply but a few arrived late. It shows that the
command had a range of unpredictable arrival
times.
19Setpoint Change Response for Wired Transmitter
and Valve
- The response to setpoint changes using a wired
transmitter and wired valve in control is shown.
20Response to Unmeasured Disturbance for Wired
Transmitter and Valve
- The response to an unmeasured disturbance using a
wired transmitter and wired valve in control is
shown.
21Setpoint Change, Valve Movement Minimized, Wired
Transmitter and Wired Valve
- The response to setpoint changes when valve
movement is minimized using a wired transmitter
and wired valve in control is shown.
22Disturbance Response, Valve Movement Minimized,
Wired Transmitter and Wired Valve
- The response to an unmeasured disturbance when
valve movement is minimized using a wired
transmitter and wired valve in control is shown
23Setpoint Change, Wired Transmitter and Wireless
Valve
- The response to setpoint changes using a wired
transmitter and wireless valve in control is
shown.
24Disturbance Response, Wired Transmitter and
Wireless Valve
- The response to an unmeasured disturbance using a
wired transmitter and wireless valve in control
is shown
25Setpoint Change Response, Wireless Transmitter
and Wired Valve
- The response to setpoint changes using a wireless
transmitter and wired valve in control is shown
26Disturbance Change Response, Wireless Transmitter
and Wired Valve
- The response to an unmeasured disturbance using a
wireless transmitter and wired valve in control
is shown
27Setpoint Change Response, Wireless Transmitter
and Wireless Valve
- The response to setpoint changes using a wireless
transmitter and wireless valve in control is
shown
28Disturbance Change Response, Wireless Transmitter
and Wireless Valve
- The response to an unmeasured disturbance using a
wireless transmitter and wireless valve in
control is shown
29Response to Setpoint Change
- The response to setpoint changes using a wireless
transmitter and wireless valve in control with
minimization of valve movement enabled is shown
30Response to Unmeasured Process Disturbance
- The response to an unmeasured disturbance using a
wireless transmitter and wireless valve in
control with minimization of valve movement
enabled is shown
31Setpoint Change Response
- The response to setpoint changes using a wireless
transmitter with a reporting rate of 16 seconds
and a wired valve in control is shown
32Setpoint Change Response, Wireless Transmitter at
16 sec, Wireless Valve, Two-Hop Network
- The response to setpoint changes using a wireless
transmitter with a reporting rate of 16 seconds
and a wireless valve in control is shown
33Exercise Control Using Wireless Throttling
Valves
- This workshop provides several exercises that can
be used to further explore the control using a
wireless measurement and wireless valve. - Open the module that will be used in this
workshop and observe the control and simulated
processes. - Step 2 Initialize the Performance Index (IAE)
and then change the SP parameter of both control
loops by 10. Observe the control response using
a plot of the setpoint, control measurements and
output. - Step 3 Note the IAE and the number of
communications for the wireless and wired
control. A significant difference should be seen
in the number of communications for wired vs
wireless control that were required to respond to
the setpoint change. - Step 4 Initialize the Performance Index and
change the Disturbance input from zero to 10.
Observe the response of the PID and PIDPlus to
this unmeasured process disturbance. - Step 5 Note the IAE and the number of
communications for the wireless and wired
control. A significant difference should be
observed in the number of communications for
wired vs wireless control that were required to
respond to the unmeasured process disturbance.
34Process Control Using Wireless Throttling Valves
- A simulation of two identical flow processes is
used to compare the control performance of
PIDPlus using a wireless transmitter and wireless
valve to PID using a wired transmitter and wired
valve.