West Control Solutions N8100 User Manual
1
-DIN,
4
1
-DIN &
8
1
-DIN
16
TEMPERATURE CONTROLLERS
Product Manual
59125-3
PREFACE
This manual comprises two volumes:
Volume 1: This supports normal operation of the
1
-DIN,
4
1
-DIN and
8
1
16
-DIN
Temperature Controllers. In normal operation, all actions taken
by the user are to be in front of the panel.
Volume 2: This supports the installation, commissioning and configuring of
the
1
-DIN,
4
1
-DIN and
8
1
-DIN Temperature Controllers. It is
16
intended for use only by personnel who are trained, equipped
and authorised to carry out these functions.
59125
1
-DIN,
4
1
-DIN &
8
1
1 6
-DIN
TEMPERATURE CONTROLLERS
PRODUCT MANUAL
VOLUME 1
OPERATING INSTRUCTIONS
In normal operation, the operator must not remove the
Controller from its housing or have unrestricted access to
the rear terminals, as this would provide potential contact
with hazardous live parts.
Installation and configuration must be undertaken by
technically-competent servicing personnel. This is covered
in Volume 2 of this manual.
Contents - Volume 1
1 OPERATOR MODE 1-1
1.1 INTRODUCTION 1-1
1.2 DISPLAYS AVAILABLE 1-2
1.3 ADJUSTING THE SETPOINT/SETPOINT RAMP RATE 1-3
1.4 ALARM STATUS DISPLAY 1-3
1.5 OVER-RANGE/UNDER-RANGE DISPLAYS 1-4
1.6 SENSOR BREAK INDICATION 1-4
1.7 MANUAL CONTROL MODE 1-4
1.8 PRE-TUNE FACILITY 1-5
1.9 SELF-TUNE FACILITY 1-6
1.10 VIEWING THE HARDWARE DEFINITION CODE 1-7
O054-V1 (iii)
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2 SET UP MODE 2-1
2.1 ENTRY INTO SET UP MODE 2-1
2.2 SET UP MODE PARAMETERS 2-2
2.3 OPERATOR MODE DISPLAYS 2-13
2.4 TUNING THE CONTROLLER MANUALLY 2-13
2.5 SELF-TUNE AND PRE-TUNE FACILITIES 2-14
2.6 EXIT FROM SET UP MODE 2-15
3 RS485 SERIAL COMMUNICATIONS 3-1
3.1 COMMUNICATIONS ENABLE/DISABLE 3-1
3.2 PHYSICAL REQUIREMENTS 3-1
3.3 INDIVIDUAL PARAMETERS 3-5
3.4 ERROR RESPONSE 3-10
(iv ) O054-V1
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1 OPERATOR MODE
1.1 INTRODUCTION
This Section covers the routine operation of the Controller, once it has been
installed and configured as described in Volume 2 of this manual. The Controller
front panel indicators and keys are shown in Figure 1-1.
Figure 1-1 Front Panel Controls and Indicators
O054-1 1-1
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1.2 DISPLAYS AVAILABLE
After the Controller has performed its power-up self-test (during which, if the
Function key is held down during power-up, the current Controller firmware
revision is displayed), the initial displays appear. The available displays are
dependent upon (a) whether the Controller has been configured for Single
Setpoint operation or Dual Setpoint operation and (b) the setting of the Setpoint
Strategy parameter in Set Up Mode.
1.2.1 Single Setpoint Operation
In single setpoint operation, the available displays are:
1 -2 O054-1
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1.2.2 Dual Setpoint Operation
In dual setpoint operation, the available displays are:
1.3 ADJUSTING THE SETPOINT/SETPOINT RAMP RATE
The setpoint/setpoint ramp rate (whichever is selected - see previously) may be
adjusted using the Raise/Lower keys. The ramp rate may be adkusted in the range
1 to 9999. Any attempt to increase the ramp rate value beyond 9999 will cause
the upper display to go blank and setpoint ramping to be switched OFF. Setpoint
ramping can be resumed by decreasing the ramp rate value to 9999 or less.
1.4 ALARM STATUS DISPLAY
If one or more of the Controller’s alarms is (are) active, the alarm status display is
included in the available display sequence. The Alarm Status display is selected
by depressing the Function key repeatedly until the display appears (see Figure
1-2).
O054-1 1-3
Figure 1 -2 Alarm Status Display
1.5 OVER-RANGE/UNDER-RANGE DISPLAYS
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The upper display will indicate if
the process variable is higher
than the input scale maximum
limit (over-range), or lower than
the input scale minimum limit
(under-range) as shown on the
right.
1.6 SENSOR BREAK INDICATION
If a break is detected in the sensor circuit, the upper display shows:
The reaction of the outputs and alarms to a detected sensor break is dependent
upon the input type and is defined in Appendix A.
1.7 MANUAL CONTROL MODE
If selection of Manual Control Mode is enabled, the Manual Control Mode may
be entered (via a bumpless transfer) by depressing the Auto/Manual key. The SET
indicator will then flash continuously whilst the Controller is in Manual Control
Mode. The output power will then be displayed and may be adjusted with the
Raise/Lower keys.A return can be made to Automatic Control Mode (via a
bumpless transfer) by simply depressing the Auto/Manual key again, which causes
the usual process variable display to appear.
1 -4 O054-1
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1.8 PRE-TUNE FACILITY
This facility may be used to set the Controller’s PID parameters to values which are
approximately correct, in order to provide a base from which the Self-Tune facility
may subsequently optimise tuning. Pre-Tune may be engaged (and subsequently
dis-engaged) as follows:
NOTE: The Pre-Tune facility will not engage if (a) the setpoint is currently
ramping, (b) the process variable is within 5% of input span of the setpoint,
or (c) an erroneous key sequence is used.
O054-1 1-5
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Since Pre-Tune is a single-shot operation, it will automatically dis-engage
itself once the operation is complete.
1.9 SELF-TUNE FACILITY
This facility is be used to optimise tuning whilst the Controller is operating. Self-Tune
may be activated as follows:
1-6 O054-1
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1.10 VIEWING THE HARDWARE DEFINITION CODE
Figure 1 -3 Viewing the Hardware Definition Code
NOTE: An automatic return is made to the normal Operator Mode
display after 30 seconds.
The Hardware Definition Code has the following significance:
Value 0 1 2 3 4 5 7 8
Input RTD/
Linear DC (mV)
Output
1
Output 2Not
fitted
Output 3Not
fitted
Relay SSR
Relay SSR
Relay SSR
Thermo-
couple
DriveDC(0 - 10V)DC(0 - 20mA)DC(0 - 5V)DC(4 - 20mA)
DriveDC(0 - 10V)DC(0 - 20mA)DC(0 - 5V)DC(4 - 20mA)
DriveDC(0 - 10V)DC(0 - 20mA)DC(0 - 5V)DC(4 - 20mA)
Linear
DC (mA)
Linear DC
(V)
Solid
State
Solid
State
Solid
State
O054-1 1-7
2 SET UP MODE
2.1 ENTRY INTO SET UP MODE
See Figure 2-1.
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Figure 2-1 Entry into Set Up Mode
2-1 O054-2
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NOTE: If, on entry into Set Up Mode, the upper
display initially shows all decimal point
positions illuminated), this indicates that one
or more of the critical configuration
parameters - typically input range or output
use/type - have been altered in value/setting and, as a consequence, all
Set Up Mode parameters have been automatically set to their default
values/settings. To clear this display, simply alter the value/setting of any Set
Up Mode parameter (see below).
2.2 SET UP MODE PARAMETERS
The parameter sequence for view/adjustment in Set Up Mode is shown in Table
2 -1 . Use the Function key to step through the parameters. In each case, the
legend will be shown in the lower display and the current value/setting will be
shown in the upper display. The value/setting may be altered using the
Raise/Lower keys. A detailed description of each of these parameters is given in
the following Subsections.
2.2.1 Input Filter Time Constant
The Controller input is equipped with a digital filter which is used to filter out any
extraneous impulses on the process variable. This filtered PV is used for all
PV-dependent functions (control, alarms etc.).
CAUTION: If this parameter value is set excessively high, the control quality
may be significantly impaired. The value chosen should be sufficiently
large to attenuate stray noise on the process variable signal but no larger.
2.2.2 Process Variable Offset
This parameter is used to modify the actual process variable value (measured at
the Controller’s input terminals) in the following manner:
Offset PV value = Actual PV value + Process Variable Offset value.
For Controllers fitted with a linear input, the displayed process variable value is
limited by Scale Range Maximum (see Subsection 2.2.30) and Scale Range
Minimum (see Subsection 2.2.31). The offset process variable value is used for all
PV-dependent functions (control, display, alarm, recorder output etc.).
NOTE: This parameter value should be chosen with care. Any
adjustment to this parameter is, in effect, a calibration adjustment.
Injudicious application of values to this parameter could lead to the
displayed process variable value bearing no meaningful
relationship to the actual process variable value. There is no front
panel indication when this parameter is in effect (i.e. has been set
to a non-zero value).
O054-2 2-2
Table 2 -1 Set Up Mode Parameters
Parameter Legend Adjustment Range Default Value
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Digital Filter Time Constant OFF, 0.5 to 100.0 secs. In
2.0 seconds
0.5 sec. increments
Process Variable Offset
Span of Controller 0
±
Output Power 0 to 100% Read only
Output Power 2
Proportional Band 1 0.0 (ON/OFF control) to
5
0 to 100% Read only
10.0%
999.9% of input span
Proportional Band 2
15,
0.0 (ON/OFF control) to
10.0%
999.9% of input span
Reset (Integral Time Const.)
Rate (Derivative Time Const.)
Overlap/Deadband
15,
1
1
1s to 99m 59s and OFF 5m 00s
00s to 99m 59s 1m 15s
-20% to +20% (of
0%
Proportional Band 1 +
Proportional Band 2)
Manual Reset (Bias)
1
0% to 100% (Output 1 only)
25%
-100% to +100% (Output 1
& Output 2)
ON/OFF Differential
2
0.1% to 10.0% of input span 0.5%
Output 1 only
Output 2 only
Output 3 only
5
5
Setpoint High Limit Setpoint to Range Maximum Range Maximum
Setpoint Low Limit Range Minimum to Setpoint Range Minimum
Recorder Output Scale Max. -1999 to 9999 Range Maximum
Recorder Output Scale Min. -1999 to 9999 Range Minimum
Output 1 Power Limit
Output 1 Cycle Time 0.5, 1, 2, 4, 8, 16, 32, 64,
1
0% to 100% of full power 100%
32 secs.
128, 256 or 512 secs.
Output 2 Cycle Time 0.5, 1, 2, 4, 8, 16, 32, 64,
32 secs.
128, 256 or 512 secs.
Process High Alarm 1 value
Process Low Alarm 1 value
Band Alarm 1 value
3
Deviation Alarm 1 value
Process High Alarm 2 value
Process Low Alarm 2 value
Band Alarm 2 value
3
Deviation Alarm 2 value
3
3
Range Min. To Range Max. Range Max.
Range Min. To Range Max. Range Min.
0 to span from Limit SP 5 units
3
3
3
±Span from Limit SP 5 units
Range Min. To Range Max. Range Max.
Range Min. To Range Max. Range Min.
0 to span from Limit SP 5 units
3
±Span from Limit SP 5 units
2-3 O054-2
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Table 2 -1 Set Up Mode Parameters (cont.)
Parameter Legend Adjustment Range Default Value
Loop Alarm Enable 0 (Disabled) or 1 (Enabled) 0
Loop Alarm Time
Scale Range Decimal Point
Scale Range Maximum
Scale Range Minimum
Auto Pre-Tune Enable/Disable 0 (Disabled) or 1 (Enabled) 0
6
4
4
4
1s to 99m 59s 99m 59s
0, 1, 2 or 3 1
-1999 to 9999 1000
-1999 to 9999 0000
Manual Control
0 (Disabled) or 1 (Enabled) 0
Enable/Disable
Setpoint Ramp Enable/Disable 0 (Disabled) or 1 (Enabled) 0
Setpoint Strategy 1, 2, 3, 4 or 5 1
Communications Enable
8
0 (Disabled) or 1 (Enabled) 1 (Enabled)
Lock Code 0 to 9999 10
Operator Mode Displays
(still accessible in Set Up
Mode):
Process Variable Read Only -
Setpoint
10
Setpoint Low Limit to Setpoint
Setpoint Low Limit
High Limit
Ramping Setpoint value
Setpoint Ramp Rate
Alarm Status Read Only (see Subsection
7
9
Read only
1 to 9999 and OFF OFF (blank)
-
1.3)
O054-2 2-4
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2.2.3 Output Power 1
This parameter is the current Output 1 power level. It is a “Read Only” parameter
and is not adjustable.
2.2.4 Output Power 2
This parameter is the current Output 2 power level (if Output 2 is fitted). It is a
“Read Only” parameter and is not adjustable. If Output 2 is not fitted, this
parameter display is not applicable.
2.2.5 Proportional Band 1
This parameter is the portion of the input span of the Controller over which the
Output 1 power level is proportional to the displayed process variable value. The
function of the Proportional Band 1 is illustrated in Figure 2 -2 .
2.2.6 Proportional Band 2
This parameter is the portion of the input span of the Controller over which the
Output 2 power level is proportional to the displayed process variable value. In
Figure 2-2 , Proportional Band 2 is shown (a) with a non-zero value (Case 1 and
Case 2) - PID control, and (b) with a zero value (Case 3) - ON/OFF control.
2.2.7 Reset ( Integral Time Constant)
This parameter is not applicable if Proportional Band 1 (see Subsection 2.2.5 ) is set
to 0 (ON/OFF control).
2.2.8 Rate ( Derivative Time Constant)
This parameter is not applicable if Proportional Band 1 (see Subsection 2.2.5 ) is set
to 0 (ON/OFF control).
2.2.9 O verlap/Deadband
This defines the portion of the Proportional Band (Proportional Band 1 +
Proportional Band 2) over which both outputs are active (or, in the case of a
deadband, neither output is active). The function of the overlap/deadband is
illustrated in Figure 2 - 2 . This parameter is not applicable if Proportional Band 1 = 0
or if Output 2 is not fitted. Note that, with Output 2 set to ON/OFF control (Figure 2-2
Case 3), the Overlap/Deadband parameter has the effect of moving the ON
Differential band of Output 2 to create an overlap (positive values) or a
deadband (negative values). When Overlap/Deadband = 0, the “Output 2 OFF”
edge of the Output 2 ON/OFF Differential band coincides with the point at which
Output 1 reaches 0%.
2-5 O054-2
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Figure 2-2 Proportional Band and Deadband/Overlap
O054-2 2-6
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2.2.10 Bias (Manual Reset)
This bias to the output power is expressed as a percentage of output power. This
parameter is not applicable if Proportional Band 1 = 0.
2.2.11 ON/OFF Differential
This is a switching differential used when one or both outputs have been set to
ON/OFF control (i.e. Proportional Band 1 or Proportional Band 2 or both = 0).
2.2.12 Setpoint High Limit
This is the maximum limit for setpoint adjustment. It should be set to a value which
prevents the setpoint being given a value which will cause damage to the
process being controlled.
2.2.13 Setpoint Low Limit
This is the minimum limit for setpoint adjustment. It should be set to a value which
prevents the setpoint being given a value which will cause damage to the
process being controlled.
2.2.14 Recorder Output Scale Maximum
This parameter defines the value of process variable or setpoint (whichever is
applicable) at which the Recorder Output reaches its maximum value; for
example, for a 0 - 5V Recorder Output, this value corresponds to 5V. The decimal
point position for the Recorder Output is always the same as that for the process
variable input range. This parameter is not applicable if the Recorder Output
option is not fitted.
NOTE: If this parameter is set to a value less than that for the Recorder
Output Scale Minimum (see Subsection 2.2.15 ), the relationship between
the process variable/setpoint value and the Recorder Output is reversed.
2.2.15 Recorder Output Scale Minimum
This parameter defines the value of the process variable or setpoint (whichever is
applicable) at which the Recorder Output reaches its minimum value; for
example, for a 0 - 5V Recorder Output, this value corresponds to 0V. The decimal
point position for the Recorder Output is always the same as that for the process
variable input range. This parameter is not applicable if the Recorder Output
option is not fitted.
NOTE: If this parameter is set to a value greater than that for the Recorder
Output Scale Maximum (see Subsection 2.2.14 ), the relationship between
the process variable value and the Recorder Output is reversed.
2 -7 O054-2
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2.2.16 Output 1 Power Limit
This parameter is used to limit the power level of Output 1 and may be used to
protect the process being controlled. If no protection is required, this parameter
may be set to 100%. IThis parameter is not applicable if Proportional Band 1 is set
to 0.
2.2.17 Output 1 Cycle Time
The cycle time value required is dependent upon the process being controlled
and the type of output being used for Output 1. For a Relay Output, the cycle
time should be as large as possible (whilst remaining compatible with the process
control requirements) in order to maximise relay life. For an SSR Output, the cycle
time may have a lower value (and thus satisfy the requirements of a fast-changing
process variable e.g. flow or pressure). This parameter is not applicable if
Proportional Band 1 is set to 0 or if Output 1 is a DC linear output..
2.2.18 Output 2 Cycle Time
The cycle time value required is dependent upon the process being controlled
and the type of output being used for Output 2. For a Relay Output, the cycle
time should be as large as possible (whilst remaining compatible with the process
control requirements) in order to maximise relay life. For an SSR Output, the cycle
time may have a lower value (and thus satisfy the requirements of a fast-changing
process variable e.g. flow or pressure). This parameter is not applicable if
Proportional Band 1 or Proportional Band 2 is set to 0 or if Output 2 is a DC linear
output.
2.2.19 Process High Alarm 1 Value
This parameter, applicable only when Alarm 1 is selected to be a Process High
alarm, defines the process variable value at or above which Alarm 1 will be
active. The operation of a process high alarm is illustrated in Figure 2-3.
2.2.20 Process Low Alarm 1 Value
This parameter, applicable only when Alarm 1 is selected to be a Process Low
alarm, defines the process variable value at or below which Alarm 1 will be
active. The operation of a process low alarm is illustrated in Figure 2-3.
2.2.21 Band Alarm 1 Value
This parameter, applicable only if Alarm 1 is selected to be a Band Alarm, defines
a band of process variable values, centred on the setpoint value. If the process
variable value is outside this band, the alarm will be active. The operation of a
band alarm is illustrated in Figure 2-3.
O054-2 2-8
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Figure 2-3 Alarm Operation
2-9 O054-2
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2.2.22 Deviation (High/Low) Alarm 1 Value
This parameter, applicable only if Alarm 1 is selected to be a Deviation High/Low
Alarm, defines a value above (positive value - Deviation High alarm) or below
(negative value - Deviation Low alarm) the setpoint; if the process variable
deviates from the setpoint by a margin greater than that defined by this
parameter, Alarm 1 goes active. The operation of Deviation Alarms is illustrated in
Figure 2-3.
2.2.23 Process High Alarm 2 Value
This parameter, applicable only when Alarm 2 is selected to be a Process High
alarm, defines the process variable value at or above which Alarm 2 will be
active. The operation of a process high alarm is illustrated in Figure 2-3.
2.2.24 Process Low Alarm 2 Value
This parameter, applicable only when Alarm 2 is selected to be a Process Low
alarm, defines the process variable value at or below which Alarm 2 will be
active. The operation of a process low alarm is illustrated in Figure 2-3.
2.2.25 Band Alarm 2 Value
This parameter, applicable only if Alarm 2 is selected to be a Band Alarm, defines
a band of process variable values, centred on the setpoint value. If the process
variable value is outside this band, the alarm will be active. The operation of a
band alarm is illustrated in Figure 2-3.
2.2.26 Deviation (High/Low) Alarm 2 Value
This parameter, applicable only if Alarm 2 is selected to be a Deviation High/Low
Alarm, defines a value above (positive value - Deviation High alarm) or below
(negative value - Deviation Low alarm) the setpoint; if the process variable
deviates from the setpoint by a margin greater than that defined by this
parameter, Alarm 2 goes active. The operation of Deviation Alarms is illustrated in
Figure 2-3.
2.2.27 Loop Alarm Enable
This parameter is the means by which the user can enable or disable the Loop
Alarm. The Loop Alarm is a special alarm which detects faults in the control
feedback loop by continuously monitoring process variable response to the
control output(s).
The Loop Alarm facility, when enabled, repeatedly checks the control output(s) for
saturation i.e. either or both outputs being at the maximum or minimum limit. If an
output is found to be in saturation, the Loop Alarm facility starts a timer; thereafter,
O054-2 2-10
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if the saturated output has not caused the process variable to be corrected by a
pre-determined amount V after a time T has elapsed, the Loop Alarm goes active.
Subsequently, the Loop Alarm facility repeatedly checks the process variable and
the control output(s). When the process variable starts to change value in the
correct sense or when the saturated output comes out of saturation, the Loop
Alarm is de-activated.
For PID control, the Loop Alarm Time T is always set to twice the value of the Reset
(Integral Time Constant) parameter. For On/Off control, the user-defined value of
the Loop Alarm Time Set Up parameter (see Subsection 2.2.28) is used.
The value of V is dependent upon the input type:
°C ranges: 2°C or 2.0 °C
°F ranges: 3°F or 3.0 °F
Linear ranges: 10 least significant display units
For single output Controllers, the saturation limits are 0% and Out1Max%. For dual
output Controllers, the saturation limits are –100% and Out1Max%.
NOTES
1. Correct operation of the Loop Alarm depends upon reasonably
accurate PID tuning.
2. The Loop Alarm is automatically disabled during Manual Control Mode
and during execution of the Pre-Tune facility. Upon exit from Manual
Control Mode or after completion of the Pre-Tune routine, the Loop Alarm is
automatically re-enabled.
2.2.28 Loop Alarm Time
When full ON/OFF control is selected (i.e. Proportional Band 1 is set to 0) and Loop
Alarm is enabled, this parameter determines the duration of the saturation
condition after which the Loop Alarm will be activated. This parameter is omitted
from the Set Up display sequence if ON/OFF control is not selected or Loop Alarm
is disabled.
2.2.29 Scale Range Decimal
Value Decimal Point Position
Point
0 xxxx
This parameter, applicable only if a linear
input is fitted, defines the position of the
decimal point in values of the process
variable, setpoint, alarm levels and
recorder outputs as shown on the right.
2 -11 O054-2
1 xxx.x
2 xx.xx
3 x .xxx
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2.2.30 Scale Range Maximum
This parameter, applicable only if a linear input is fitted, defines the scaled input
value when the process variable input hardware is at its maximum value. This
parameter can be set to a value less than (but not equal to) Scale Range
Minimum, in which case the sense of the input is reversed. Decimal point position
is defined by the Scale Range Decimal Point parameter (see Subsection 2.2.29 ).
2.2.31 Scale Range Minimum
This parameter, applicable only if a linear input is fitted, defines the scaled input
value when the process variable input hardware is at its minimum value. This
parameter can be set to a value greater than (but not equal to) Scale Range
Maximum, in which case the sense of the input is reversed. Decimal point position
is defined by the Scale Range Decimal Point parameter (see Subsection 2.2.29 ).
2.2.32 Auto Pre-Tune Enable/Disable
This parameter determines whether or not the Controller’s Pre-Tune facility is
activated automatically on power-up or not.
2.2.33 Manual Control Enable/Disable
This parameter determines whether operator selection of manual control is
enabled or disabled.
2.2.34 Setpoint Ramp Enable/Disable
This parameter enables/disables use of the setpoint ramping feature at user level.
2.2.35 Setpoint Strategy
This parameter enables the user to select the required Operator Mode setpoint
display strategy - see Subsections 1.2.1 (Single Setpoint operation) and 1.2.2 (Dual
Setpoint operation).
2.2.36 Communications Enable/Disable
This parameter enables/disables Write operations (i.e. the changing of parameter
values/settings) via the RS485 communications link, if the Communications Option
PCB is fitted. Parameters can be interrogated via the link, regardless of the setting
of this parameter.
2.2.37 Lock Value
This parameter defines the four-digit code required to enter Set Up Mode.
O054-2 2-12
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2.3 OPERATOR MODE DISPLAYS
Once the complete cycle of Set Up Mode parameters has been displayed, the
user may then step through the Operator Mode displays (see Subsection 1.2),
making adjustments where required, before re-starting the Set Up Mode
parameter cycle, as shown in Table 2-1.
2.4 TUNING THE CONTROLLER MANUALLY
2.4.1 Controllers Fitted with Output 1 Only
Before starting to tune the Controller to the load, check that the Setpoint High and
Low Limits (SPhi and SPLo) are set to safe levels - see Subsections 2.2.12 and
2.2.13 .
The following simple technique may be used to determine values for proportional
band (Pb1), derivative time constant (rAtE) and integral time constant (rSEt).
NOTE: This technique is suitable only for processes which are not harmed by
large fluctuations in the process variable. It provides an acceptable basis
from which to start fine tuning for a wide range of processes.
1. Set the setpoint to the normal operating process value (or to a lower
value if overshoot beyond this value is likely to cause damage).
2. Select ON/OFF Control (i.e. set Pb1 = 0).
3. Switch on the process. The process variable will oscillate about the
setpoint. Note (a) The peak-to-peak variation (P) of the first cycle i.e. the
difference between the highest value of the first overshoot and the lowest
value of the first undershoot, and (b)tThe cycle time (T) of this oscillation in
minutes (see Figure 2-4)
4. The control parameters should then be set as follows:
=
= T minutes
P
x 100
ScaleRange
T
=
minutes
6
NOTE: After setting up the parameters, set the Controller to Operator Mode
(see Subsection 2.6) to prevent unauthorised adjustment to the values.
2 -13 O054-2
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