West Pro-EC44 Operating Manual

2-Loop Graphical Profile Controller & Recorder

Concise Product Manual (59541-4) Page 1 of 6

A Full Product Manual is also available from your supplier.

The following symbols are use on the product labels:

Caution: Potential danger to life
or limb. Refer to installation

manual when connecting

Equipment protected through­out by double insulation

Alternating current

Both direct and alternating
current

1. INSTALLATION

CAUTION: Installation should be only performed by technically

competent personnel. It is the responsibility of the installing engineer
to ensure that the configuration is safe. Local regulations regarding
electrical installation & safety must be observed - e.g. US National
Electrical Code (NEC) and/or Canadian Electrical Code. Impairment of
protection will occur if the product is used in a manner not specified by
the manufacturer.

Installing Plug-in Modules

Board Mounting Struts (x8) &
Front Removal Latch (x1)

Plug-in Module A
2nd Universal Input & Base

Option 2 Board
Plug-in Module 3
1st Universal Input & Base

Option 1 Board
Power Supply Board

Plug-in Module 1
Plug-in Module 2
USB/Digital Input C Option

Board

To access the plug-in modules, first remove the instrument from the housing.

a. Pull front out to engage Front Latch. This prevents removal without a tool.
b. Press latch with screwdriver through top vent hole. Remove front from case.
c. Detach main boards by lifting first the upper, and lower mounting struts.
d. Plug required modules into the correct connectors, as shown below.
e. Locate the module tongues in corresponding slot(s) on the opposite board.
f. Hold the Power and Input boards together while relocating on their mountings.
g. Push the boards forward to ensure correct connection to the Display board.
h. Replace the instrument by aligning the boards with the guides in the housing,

then slowly push the instrument back into position.

NOTE: Plug-in modules are automatically detected at power up.

Main Board Connectors

POWER SUPPLY

BOARD

Transformer Colour

Code

100-240V (Yellow)

24-48V (Blue)

Display Board

Connections

1st UNIVERSAL

INPUT / BASE

OPTION 1

BOARD

Module Slot 3
Connector PL4B

Module Slot A

Connectors
PL5, & PL6

Module Slot 1

Connectors PL7 & PL8
PC Configurator

Socket SK1

Module Slot 2
Connector PL4A

NOTE: Plastic

pegs prevent
fitting of older non­reinforced single relay
modules –remove the
peg to fit dual relays

Re-fitting the Main Boards

This product is designed to allow the user to reconfigure some hardware options in
the field by changing the modules fitted in slots 1, 2, 3, & A. The main boards
(display/CPU, power supply, inputs 1 & 2 and digital input/USB) are factory fitted, but
may be removed while reconfiguring the plug-in modules. Take care when re-fitting
these boards. Observe the power supply board transformer colour, and case labelling
to check the supply voltage, otherwise irreparable damage may occur.

CAUTION: In the event of a fault, replacement of defective main boards

should only be carried out by trained personnel.

Panel Mounting

Gasket

Mounting Panel

Ratchets

Instrument

Housing

1. Insert instrument into the
panel cut-out.

2. Hold front bezel firmly
(without pressing on the
display area), and re-fit
mounting clamp. Push the
clamp forward, using a tool
if necessary, until gasket
compresses and instrument
is held firmly in position.

NOTE: For an effective IP66 seal against dust and moisture, ensure

gasket is well compressed against the panel, with the 4 tongues
located in the same ratchet slot.

Rear Terminal Wiring

CAUTION: The instrument is double insulated. All external circuits

connected must provide double insulation.
Failure to comply with the installation instructions may impact the
protection provided by the unit.

CAUTION: Check correct operating voltage on the side label before

connecting power. A UL listed anti-surge fuse should be fitted to the
power input. An IEC60947-1 & IEC60947-3 compliant isolation switch
should be fitted close to the unit, in easy reach of the operator, and
appropriately marked.

NOTE: The wiring diagrams show all possible option combinations. The

connections required depend on the options & modules fitted.
Use single strand (1.2mm / AWG18 max size) copper wire, except for
thermocouple inputs, where the correct thermocouple or compensating
cable and connectors should be used.

Central Terminals 1 to 24

CAUTION: External computing devices connected to the

communications port must comply with the standard, UL 60950.

Outer Terminals 25 to 42

2. POWER UP SEQUENCE

Following the power-up self-test and logo screen, the instrument normally enters
Operation Mode, from which the user can select the instrument’s Main Menu (refer to
the Screen Sequences on page 5). The exceptions to this are the first power-up after
purchase where the Setup Wizard is shown, or if a plug-in module error is detected.

Plug-in Module Errors

If an invalid or unknown module is detected in one of the plug-in module slots the
message “Fault Found, Press R, for details” followed by “Replace faulty module in
Module Slot n, Press R,” (where n identifies the problem slot). The Service Contact

information is displayed next showing details of who to contact if a fault persists

CAUTION: Do not continue using the product until the issue causing

the error is resolved.

3. OPERATION MODE

This mode is entered at power on, or can be accessed from the Main Menu.
The initial screens shown in operation mode vary depending on the options fitted and
the configuration. Subsequent screens display and may allow the selection or
adjustment* of Setpoints, setpoint ramps, enable/disable control, auto/manual
operation, alarm status, profiler & recorder status and graphical trend views.
Some screens will persist until the user navigates away, others will ‘time-out’ back to
the main screen (refer to Operation Mode: in Screen Sequences).

Press R or L briefly to move forward/back through parameters. Where adjustment is
possible*, press D or U to alter the values. The next/previous screen follows the last
parameter - or hold down R or L >1sec to skip straight to next/previous screen

accepting ALL values shown.

* If required, all Operation Mode parameters can be made read only (see Display
Configuration on page 6) and others may be removed from this mode altogether.

NOTE: Configuration must be completed before starting normal

operations.

Single Control Loop: Normal Operation

LED Indicators

LED Function Labels

Process Variable Value

Engineering Units

Actual Setpoint Value

Control Deviation Graph

scaled ±5% of input span

Power Graph

1-Loop Operation

Single Control Loop: Profiler Status

LED Indicators

LED Function Labels

Process Value & Setpoint

Engineering Units

Profile Name & Progress

Segment No, Type &

Progress or Delay Time

Profile Status Indicator:

► Run, ▌▌ Held, ■ Stopped

1-Loop Profile Status

If enabled in Display Configuration, the prior screen allows the user to Select, Run,
Hold or Abort a profile. The next screen shows the profile event output status.

Two Control Loops: Normal Operation

LED Indicators

Process Variable* & Actual

Setpoint Values*

LED Function Labels

Indicators for Alarm and
Remote Setpoint active*

Loop Descriptions*

Engineering Units*

Control Deviation (±5% of

span) & Power Graphs*

* = in loop 1 & 2 screen area

2-Loop Operation

Two Control Loops: Profiler Status

LED Indicators

LED Function Labels

Profile Status Indicators*:

► Run, ▌▌ Held, ■ Stopped

Engineering Units*

Process Variable Values
& Setpoints*

Loop Descriptions*

Profile Name & Progress
Segment No. Type &
Progress or Delay Time

* = in loop 1 & 2 screen area

2-Loop Profile Status

Cascade Control: Normal Operation

LED Indicators

LED Function Labels

Master Process Value

Cascade Status

Slave Process Value

Master Setpoint (Slave SP if

Cascade Open)

Control Deviation (±5% of
span) & Power Graphs

Cascade Control

Ratio Control: Normal Operation

LED Indicators

LED Function Labels

Relative Process Value

Ratio & Setpoint Labels

Relative Setpoint

Control Deviation (±5% of
span) & Power Graphs

Ratio Control

Trend Views

Active Alarm(s)

Trend Upper Scale Value

Cursor Line

Process Variable Trend

PV Value At Cursor Line

Setpoint Trend (dotted)

Trend Lower Scale Value

Loop No, & Time Markers

(10 samples per marker)

Sample Interval (or Time
At Cursor Line)

Trend View

The Trend Views graph PV; PV & SP; or Max/Min PV between samples, plus active
alarms. Graph format and sample intervals are set in Display Configuration. Trend
scale values adjust automatically to visible data (between 2 to 100% of input span).

120 of 240 historical data points visible. Pressing D or U moves the Cursor Line
back through the last 240 data points.

NOTE: Data is not retained at power down or if the sample interval is

changed.

Manual Control

Depending on the Control Configuration settings, automatic or manual control can be
selected from the Auto/Manual selection screen, or via a digital input. Switching to or
from manual mode is via Bumpless Transfer.
In Manual mode the Setpoint display is replaced by a -100 to 100% power output
level, labelled “Man”.

Press D or U to set the required manual power.
When using VMD control, Manual mode replaces the Setpoint display with the valve
movement status (Opening, Closing or Stopped), and is labelled “Man”.

The U key opens the valve and the D key closes the valve.
If Manual control is selected when in Cascade mode, the slave loops % power value
is shown. This is the power output fed directly to the control actuator (e.g. heaters).

NOTE: Selecting Manual Control will cause a running profile to hold

until control is returned to automatic mode.

CAUTION: Manual mode overrides the automatic control loop. It also

ignores any output power limits, valve open/close limits and the control
enable/disable setting. The operator is responsible for maintaining the
process within safe limits.

Over/Under Range & Input Fail Indications

If the process or auxiliary inputs are >5% above or below the scale max/min, the

displayed value is replaced with the word “HIGH” or “LOW”.
If a signal break is detected, the value is replaced with “OPEN”; except in Ratio

control where an open input 1 or 2 is shown as “x1-Open” or “x2-Open”.
An un-calibrated input is replaced by “ERROR”.
In OPEN or ERROR conditions, the Control Outputs go to the pre-set power value
(see Control Configuration on page 6).

CAUTION: Correct the problem causing the error condition before

continuing normal operation.

Customising Operator Mode

The user can choose to enable or disable some operator mode screens from the
Display Configuration menu (see page 6). These are: cascade mode switching;
auto/manual control selection; setpoint ramp-rate values; selecting the setpoint
source; control enable/disable; clear latched outputs; manually triggering a recording;
recorder status information and trend views – these are marked ◘ in the screen list on
page 5 to indicate that they are optional.
In addition, up to 50 configuration mode parameters can be copied into operation
mode using the PC software. Any parameters selected in this way are shown at the
end of the normal operator mode screen sequence.

NOTE: Configuration mode parameters copied into operation mode

are not pass code protected.

It is recommended that you only enable operator mode screens if they are important
for daily operation. Consider using Supervisor Mode (see section 21) for parameters
that the operator may need less often or that you want to limit access to.

4. AUTOMATIC TUNING

To automatically optimise the PID tuning (PI tuning in VMD mode) for the process, you
can use Pre-Tune, Self-Tune or Auto Pre-Tune independently for each loop.
Pre-tune performs a single start-up disturbance test. It stops running when the test
has completed. The user chooses which PID set the new tuning terms will be applied
to, and this selection does not change the selected “active PID set”. There are two
modes; Standard Pre-Tune which tests the process response half-way from the
activation point (the process value when pre-tune began running) to the current
setpoint; or Pre-Tune at Value which allows the user to specify the exact process
value at which the test will occur.

CAUTION: Consider possible process over-shoot when selecting the

value to tune at. If there is a risk of damage to the product or equipment
select a safe value.

If Auto Pre-Tune is selected, a Standard Pre-tune will attempt to run at every power
up. If Self-Tune is selected it constantly monitors the process and adjusts the tuning
when control errors occur. Auto pre-tune and self-tune apply the new tuning terms to
the current Active PID set. Auto pre-tune and self-tune are not possible with cascade.

NOTE: To pre-tune a cascade, first select “Cascade-Open” to tune the

PID set(s) on the slave. After the slave has successfully tuned,
remember to pre-tune the master/slave combination (this time select
“Cascade-Closed”). The cascade remains open until you do this.

See PID Sets & Gain Scheduling on this page and Automatic Tuning on page 5. Refer
to the Full Product Manual (from your supplier) for more about tuning.

NOTE: Automatic tuning will not engage if either proportional band is

set to On/Off control. Also, pre-tune (including and auto pre-tune
attempt) will not engage if the setpoint is ramping, a profile is running,
or the Process Variable is <5% of span from setpoint.

5. PID SETS & GAIN SCHEDULING

Up to 5 sets of PID tuning terms (primary & secondary proportional bands or on-off
differential, integral & derivative times, overlap/deadband) can be entered for each
control loop, allowing the unit to be pre-set for differing conditions. For each loop one
set can be selected as the “Active PID” set, or alternatively, if the process conditions
change significantly during use (e.g. if it is partially exothermic as the temperature
rises) Gain Scheduling can be employed.

Gain scheduling ‘bumplessly’ switches
PID sets automatically at successively
higher setpoint or process values, giving
optimal control across a wide range of
process conditions. PID set 1 is used
from the scaled input lower limit until the
“breakpoint” for set 2 is passed and that
set becomes active. Set 2 is used until
the breakpoint for Set 3 is reached etc. If
any breakpoint is set to OFF, the
subsequent PID sets are not used.

See Automatic Tuning section 4 for tuning the PID sets.

NOTE: ON/OFF control is possible with the individual PID sets but

cannot be used with gain scheduling. On/off control is replaced with
the default proportional band if gain scheduling is turned on.

PID Set 1

PID Set 2

PID Set 3

PID Set 4

PID Set 5

PV or SP

Scale Upper
Limit

Scale Lower
Limit

Breakpoints

2-Loop Graphical Profile Controller & Recorder

Concise Product Manual (59541-4) Page 2 of 6

6. APPLICATION SETUP

Setup Wizard

An easy Setup Wizard runs automatically at first ever power-up. Follow the wizard to
setup parameters required for basic applications. The screens/parameters marked “w”
in the Screen Sequences lists are included, see pages 5 & 6. The wizard can be run
again at any time from the main menu. An option to reset all parameters to default
(recommended) is offered when manually running the wizard.

Pre-commissioning Considerations

The next sections provide guidance for more complex applications where the wizard is
not sufficient. It is important to understand how the instrument is to be used before
commencing with the setup. Consideration must be given to the following questions:

If fitted, how will the 2nd input be used?

 One loop only (2nd input not used in this application)
 Two independent control loops.
 Valve feedback for loop 1
 A “redundant” backup for the 1st input (see section 10).
 Cascaded with the first control loop (see section 7).
 A reference input for ratio control (see section 8).

How will the instrument control the process?

 Primary only or primary & secondary control outputs (see section 12).
 Direct valve motor drive outputs (see section 11).

The table below shows the main input and control configuration settings for these
application types (see page 6 for the configuration menus).

Process Type*

Loop 1 / Master

Loop 2 / Slave

(only if 2nd
input fitted)

Control
Configuration:
Control Select

Control
Configuration:
Control Type

Control
Configuration:
Control Select

Control
Configuration:
Control Type

One Loop*

Input 2
Configuration |
Input 2 Usage
= Not Used

Standard PID
Control Select
= Control Standard
Primary Only
Control Type
= Single

Primary / Secondary
Control Type
= Dual

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Two Loops*

Input 2
Configuration |
Input 2 Usage
= Standard

Standard PID
Control Select
= Control Standard
Primary Only
Control Type
= Single

Standard PID
Control Select
= Control Standard
Primary Only
Control Type
= Single

Primary / Secondary
Control Type
= Dual

Primary / Secondary
Control Type
= Dual

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

+Feedback*

Input 2
Configuration |
Input 2 Usage
= Feedback

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Redundant*

Input 2
Configuration |
Input 2 Usage
= Redundant
Input

Standard PID
Control Select
= Control Standard
Primary Only
Control Type
= Single

Primary / Secondary
Control Type
= Dual

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Cascade*

Input 2
Configuration |
Input 2 Usage
= Standard

AND
Loop 1 / Master
Configuration |
Control Mode
= Cascade

Standard PID
Control Select
= Control Standard
Primary Only
Control Type
= Single

Primary / Secondary
Control Type
= Dual

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Ratio*

Input 2
Configuration |
Input 2 Usage
= Standard

AND
Loop 1 / Master
Configuration |
Control Mode
= Ratio

Standard PID
Control Select
= Control Standard

Valve Motor Drive
Control Select
= VMD (TPSC)
Control

Which outputs will be used for control, and are alarms or event outputs needed?

 Output configuration (see page 6).
 Alarms & Profile Events (see pages 5 & 6).

Where will the controller setpoint come from?

 Local setpoint(s) only, or a remote setpoint input (see page 6).
 Profile Control (see section 15).

Is Input re-configuration required:

 Analogue input calibration & scaling (see section 13).
 Digital input functions (see section 9).

Which other features are to be used?

 Data Recorder (see section 17).
 Serial Communications (see section 19).
 USB Interface (see section 16).

CAUTION: Configuration & commissioning must be completed before

proceeding to Operation Mode. It is the responsibility of the installing
engineer to ensure that the configuration is safe.

7. CASCADE CONTROL MODE

Applications with long time lags (e.g. with two or more capacities such as heated
jackets) can be difficult to control with a single control loop. The solution is to split the
process into two or more cascaded loops consisting of a Master and Slave(s) acting

on a common actuator. Ideally, the slave loop’s natural response time should be at

least 5 times faster than the master.
The master loop compares the process temperature with the desired setpoint and its
correcting variable (0 to 100% PID output) becomes the slave loops effective setpoint
(scaled to suit the process). This setpoint is compared to the slave’s process input,
and the controlling actuator is adjusted accordingly.

NOTE: Cascade control is available on models fitted with the 2nd

Universal Input. The master connects to input 1; the slave to input 2.

Example

In this example the controlling actuator is a heater, indirectly heating the product via
an oil jacket. The maximum input to the slave represents 300ºC, thus restricting the
jacket temperature. At start-up the master compares the product temperature
(ambient) to its setpoint (250ºC) and gives 100%. This sets the maximum slave
setpoint (300ºC), which is compared to the oil temperature (ambient) and the slave
requests maximum heater output.
As the oil temperature rises towards the slave setpoint, its output falls. Eventually, the
product temperature will also begin rising, at a rate dependant on the transfer lag

between the oil jacket and the product. This causes the master’s PID output to

decrease, reducing the slave setpoint. The oil temperature is reduced towards the
new slave setpoint. This continues until the system becomes balanced. The result is
quicker, smoother control with the ability to cope with changes in the load. Overshoot
is minimised and the jacket temperature is kept within acceptable limits.

Cascade Operation

Normal Cascade Operation

During operation, the master and slave are coupled together and. "Cascade" is
displayed. The master process value and setpoint are most relevant to the user. This
setpoint is directly adjustable, and the process value of the slave controller is
displayed for information only.

Cascade-Open

The cascade can be disconnected (via digital inputs or menu selection), switching
from normal operation to direct control of the slave. "Cascade-Open" is displayed.
The process is then controlled and adjusted solely by the slave controller using its
internal setpoint (displayed as SlaveSP). Switching back to Cascade is “Bumpless”.

CAUTION: The master process value is not under control when the

cascade is open, but will be affected by the slave process. The
operator is responsible for maintaining safe conditions.

Manual Mode

The controller can be put into manual mode (via digital inputs or menu selection),
bypassing the cascade to take direct control of the slave loop’s correcting variable.
Manual power is adjusted from -100 to 100%. "MAN" is displayed in manual mode.

CAUTION: Manual mode disables the cascade loop. It also ignores any

output power limits, valve open/close limits and the control
enable/disable setting. The operator is responsible for maintaining the
process within safe limits.

Cascade Tuning

The user can tune manually or use the pre-tune feature (see Automatic Tuning).

In either case the slave control loop must first be optimised on its own, followed by
the master loop in combination with the previously tuned slave.

To pre-tune a cascade:

1. Go to the Automatic Tuning menu

2. Select “Cascade-Open” to tune the PID set(s) on the slave.

3. After the slave has successfully tuned, pre-tune the master/slave combination
(this time select “Cascade-Closed”). The cascade remains open until you do this.

To manually tune a cascade:

1. Open the cascade, breaking the link from master to slave.

2. Set the slave controller setpoint manually to an appropriate value.

3. Tune the slave for relatively fast control (‘proportional only’ is often sufficient).

4. Close the cascade and tune the master/slave combination.

8. RATIO CONTROL MODE

A ratio control loop is used where the quantity of one of the material is to be controlled
in proportion to the measured quantity of a second material. The controller mixes the
materials at the desired ratio by adjusting the flow of input 1. The flow of input 2 may
be controlled separately, but is not controlled by this loop.
The process value used by the controller is therefore determined by the ratio of the
two inputs rather than being measured as one process variable.

NOTE: Ratio control is available on models fitted with the 2nd Universal

Input. Connect the Air flow to input 1 and the fuel to input 2.

Stoichiometric combustion

Below is an example of standard ratio control using stoichiometric combustion.
For optimum combustion the fuel-air ratio must be controlled. The ratio is selected so
that there are no inflammable residues in the waste gas.

It is normal in this application to display the process value and setpoint as relative
values rather than the physical ratio or absolute values. A scaling factor is set such
that the displayed value will be 1.00 at the correct stoichiometric ratio for the
application.

Inputs 1 and 2 are configured and scaled to match the attached flow meters.
In this example a 4 to 20mA signal at x1 represents 0 to 1000m3/h of airflow controlled
by a valve. The second 4 to 20mA signal at x2 represents 0 to 100m3/h of fuel oil. The
fuel flow is not affected by this control loop.
Atomizing air is fed in with the fuel oil at a constant rate ‘NO’. This must be considered
when calculating the correct fuel/air mix. Total airflow is x1 + NO.
The stoichiometric factor, SFac is entered to match the desired ratio. E.g for 10 parts
total airflow to one part fuel, SFac would be 10.

The setpoint (entered as a relative value such as 1.00) is multiplied by SFac when
calculating the control deviation. E.g. with a setpoint of 1.00 and SFac of 10 the
controller attempts to make the physical ratio 10. With a setpoint of 1.03 it would
attempt to make the ratio 10.3 for 3% excess air.

The instantaneous (controlled) process value is calculated from the physical ratio,
divided by SFac. Like the setpoint, this is displayed as relative value.
E.g. if SFac is 10, 59.5m3/h air is measured at x1, 0.5m3/h atomising air is applied at
NO and 6m3/h fuel is measured at x2, the instantaneous process value would be:

  

  

 

    

  

  

9. DIGITAL INPUTS

Digital inputs are driven to one of two states (active or inactive) by an applied voltage
signal or a contact opening/closing. They can be used for profile selection (see Digital
Input Setup sub-menu on page 6), with any remaining inputs available for functions
such as selecting setpoint sources, running a profile or driving an output on/off (the
Digital Input Specifications on page 4 lists all possible functions).

A diagnostic screen assists commissioning
and fault finding by showing the current
signal state for all digital inputs.

Slot A, C1 to C8 & Soft digital input status
( = Active, Ø = Unavailable)
Profile select bit format (BCD or Binary)
Profile selected (e.g. BCD 6 from C1-C3)

Digital inputs can be inverted to reverse

their action with an “on” input turning off.

Step thorough each input using the R
key. Press U to invert  the highlighted
input and D to un-invert . Hold R down
to skip to next screen accepting the
values shown.

Highlighted Input

Four “soft” digital inputs can be configured
by combining physical inputs, alarms &
events using Boolean logic. The input AND
selections are globally OR’d with input OR
selections, alarms & events. By using the
invert inputs function, NAND & NOR
equivalents can be created.

Soft inputs and any physical digital inputs
not allocated for profile selection can be
used to change the instrument status.
Functions include: Setpoint or Auto/man
select; control on/off; automatic tuning;
clearing latched outputs; profile control;
data recording; forcing outputs on/off or
mimicking key presses.

10. REDUNDANT INPUT

If the 2nd universal input is fitted, it can be used with a backup sensor so that if the
main sensor fails, the instrument automatically switches to the redundant sensor. In
this condition, if input 1 has a signal break alarm configured it will activate, but any
other process input or control status alarms seamlessly switch to the 2nd input. This
input continues to be used until the signal to input 1 is restored. The user may not
even be aware of the sensor fault, so signal break alarms should be configured for
both inputs to provide notification.
The redundant sensor must be of the same type, and be correctly located in the
application ready to take over if needed. If this option is selected, the 2nd input cannot
be used for other functions.

NOTE: If both signals are lost at the same time, the PV is replaced with

“OPEN” and the normal sensor break actions occur.

11. VALVE MOTOR / 3-POINT STEPPING CONTROL

When directly controlling motorised modulating valves, set the Control Mode to VMD
in configuration mode to enable the 3-point stepping Valve Motor Drive control
algorithm. This provides switched outputs to move the valve further open, or further
closed when a control deviation error is detected. If the error is reduced to zero no
further output is required until the load conditions change.

NOTE: Some modulating valves have positioning circuitry to adjust the

valve position. These need a DC linear mA or voltage output and use the

standard control algorithm (Set Control Mode to Standard).

VMD doesn’t allow On-Off Control (Prob. Band minimum is 0.5% of input span) and
usually requires PI control, where the Derivative parameter is turned OFF.

Special Wiring Considerations for Valve Motor Control

Valve Motor Drive (VMD) mode requires two identical outputs to be assigned to
position the valve. One to Open and one to Close the valve. These outputs can
be two single relays, two triacs, two SSR drivers or one dual relay, but it is
recommended to use two single relays (SPDT change-over contacts), and to
interlock the wiring as shown. This prevents both motor windings from being
driven at the same time, even under fault conditions.

CAUTION: The windings of a valve motor effectively form an

autotransformer. This causes a voltage doubling effect when power is
applied to either the Open or Close terminal, causing twice the
supplied voltage at the other terminal.

Switching actuators directly connected to the valve motor must only be used up to
half of their rated voltage. The internal relay and triac outputs are rated at 240VAC
Therefore, the maximum motor voltage when using them is therefore 120V unless
interposing relays are used. Interposing relays or other devices used to control the
valve must themselves be rated for twice the motor supply voltage.

Position Feedback

The VMD mode in this instrument uses a boundless, open-loop, algorithm. It does not
require any kind of position feedback in order to correctly control the process and can
therefore avoid problems associated with faulty feedback signals.
However, where feedback is available it can still be displayed as a percentage (0 to
100%) of the possible valve opening.
Valve Position Feedback is usually provided by means of a potentiometer
mechanically linked to the valve. The output of a related flow meter can also be used
to indicate the relative valve position. Flow meters typically have linear 0-20/4-20mA
or 0-5/0-10V signals. To display the position/flow signal the 2nd input is must be
configured for this purpose.
The input is adjusted and scaled to read 0 to 100% for valve fully closed to fully open
or for the flow rate equating to fully closed and open.

Valve Limiting

When Valve Position Indication is to be used the signal can be used by the
instrument to limit the valve movement. Valve limits can be set beyond which the
controller will not attempt to drive the valve.

CAUTION: These limits must be used with care. They are effectively

control power limits. Do not set values that prevent proper control of
the process!

12. CONTROL TYPE

The control type defines if a control loop has single (unidirectional) or dual
(bidirectional) control outputs. Single control has a primary output only. This can drive
the process in one direction (e.g. heating only, cooling only, increasing humidity etc).
Dual control has both primary and secondary outputs which can force the process to
increase or decrease (e.g. heating & cooling, humidifying & dehumidifying etc). This
selection isn’t required for VMD control which provides direct 3-point stepping control
for valves, and always has one output to increase and another to decrease the
process value (see section 11).

“Open” Relay

“Close” Relay

120V Supply

Open Valve Winding

Close Valve Winding

Valve Common

0-300°C

Slave SP

0-100%
Output

SLAVE SENSOR

MASTER SENSOR

Master

Setpoint

250°

HEATER

OIL JACKET

MASTER

IP1

OP

SP

SLAVE

IP2

OP

SP

PRODUCT

Atomization Air

NO

Burner

Air

Fuel