Relative Setpoint Module
The Relative Setpoint Module helps provide extensive non-critical control, secondary protection, and analysis capabilities by allowing you to initiate an action in response to a specific condition.
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Overview
This module is particularly useful for performing actions based on differences between a value (e.g. kW on phase A) relative to a reference value (e.g. kW demand for all three phases). You can use the outputs from this module for demand control of equipment, or any other applications requiring setpoint activity relative to a varying value.
A Relative Setpoint Module monitors a single numeric Source input and compares it to a programmed setpoint condition (the value in the Nominal input). The setpoint condition is defined by pickup and dropout levels, relative to the Nominal input, and by a time delay. If the Source value falls outside the programmed range for the specified time, the setpoint condition is met; the Status output register changes to on, the Over and Under outputs indicate whether an Over or Under setpoint condition exists, and a trigger pulse is generated.
NOTE: The registers and settings available in this module depend on the device or node you are configuring, as well as its firmware and template versions. Not all registers or settings are available on all devices or the Virtual Processor, and labels may vary.
Inputs
Source
This input is monitored for the setpoint condition. It can be a numeric register from any other module’s outputs. Linking this input is mandatory.
Nominal
This input provides a reference value for the setpoint. It can be either a numeric or numeric bounded setup or output register from any other module. Linking this input is mandatory.
Enable
This input can enable or disable the Relative Setpoint module. If the Enable setup register is set to disabled, this input is ignored and the module is disabled. Disabling the module forces the Status, Over and Under output registers to not available, overriding the Setpoint condition. This input is optional; if you leave it unlinked, the module is enabled by default.
Setup registers
Eval Mode
This register determines how the values in the Over Pickup, Over Dropout, Under Pickup and Under Dropout setup registers are interpreted. It can be set to value or percentage. If Eval Mode is set to value, the values in the Pickup and Dropout registers are interpreted as numbers, and these numbers are either added to or subtracted from the Nominal value. If Eval Mode is set to percentage, the Pickup and Dropout values are interpreted as percentages of the Nominal value.
Over Pickup
This register, together with the Nominal input, defines the level that the Source input must exceed (for a time specified by SusUntlON) in order for the Status output to go ON (i.e. the setpoint becomes active). If Eval Mode is set to value, the level required for the Status output to go on is given by adding the Over Pickup value to the Nominal value (Nominal + Over Pickup). If Eval Mode is set to percentage, the level required for the Status output to go on is given by:
Over Dropout
This register, together with the Nominal input, defines the level that the Source input must fall below (for a time specified by SusUntlOFF) in order for the Status output to go off (i.e. the setpoint becomes inactive). If Eval Mode is set to value, the level required for the Status output to go off is given by adding the Over Dropout value to the Nominal value (Nominal + Over Dropout). If Eval Mode is set to percentage, the level required for the Status output to go off is given by:
Under Pickup
This register, together with the Nominal input, defines the level that the Source input must fall below (for a time specified by SusUntlON) in order for the Status output to go ON (i.e. the setpoint becomes active). If Eval Mode is set to VALUE, the level required for the Status output to go ON is given by subtracting the Under Pickup value from the Nominal value (Nominal - Under Pickup). If Eval Mode is set to PERCENTAGE, the level required for the Status output to go ON is given by:
Under Dropout
This register, together with the Nominal input, defines the level that the Source input must exceed (for a time specified by SusUntlOFF) in order for the Status output to go off (i.e. the setpoint becomes inactive).
If Eval Mode is set to value, the level required for the Status output to go off is given by subtracting the Under Dropout value from the Nominal value (Nominal - Under Dropout). If Eval Mode is set to percentage, the level required for the status output to go off is given by:
SusUntlON (sustain until on)
This register defines the amount of time in seconds the Source input must either exceed the Over Pickup level, or fall below the Under Pickup level, for the setpoint to become active (i.e. for the Status output register to change from off to on).
SusUntlOFF (sustain
until off)
This register defines the amount of time in seconds the Source input must be less than the Over Dropout level, and greater than the Under Dropout level, for the setpoint to become inactive (i.e. for the Status output register to change from on to off).
EvPriority (event priority)
This register allows you to assign a priority level to the following events produced by the Relative Setpoint module:
- The Status output register changes to on because the setpoint condition is met.
- The Source or Nominal input becomes not available while the status output is ON.
- The Status output register changes to off because the setpoint condition is no longer met.
- The Relative setpoint module is reconfigured or disabled while the Status output register is on.
The priority level you specify applies to all of the above events. If the EvPriority setup register is set to zero (0), none of the above events will be logged.
Enable
This register, if set to disabled, disables the Relative Setpoint module regardless of the Enable input register. Disabling the module forces the Status, Over and Under output registers to not available, overriding the Setpoint condition. If this register is set to enabled, the Relative Setpoint module is enabled or disabled based on the Enable input register.
Output registers
Status
This Boolean register is on when the Setpoint condition is met, and off when the Setpoint condition is not met. If the Enable input is off, the Enable setup set to disabled, or if either the Source or nominal inputs are not available, the Status output register will change to not available. Also, if any input link or any of the setup registers are changed while the Status register is on, it will automatically change to off.
NOTE: If any changes are made to the Relative Setpoint module while the Status output register is on, the Status output register will be forced off and the module’s inputs will be reevaluated for the setpoint condition.
Over
This Boolean register is on if the setpoint condition is met with the Source input greater than the Nominal input.
Under
This Boolean register is on if the setpoint condition is met with the Source input less than the Nominal input.
Trigger
When the Setpoint condition is met, the Trigger output register generates a pulse.
Event
All events are recorded in the Event register. Possible events and their associated priority numbers are:
| Event priority group | Priority | Description |
|---|---|---|
| Setup Change | 10 | Input links, setup registers or labels have changed. |
| Information | 25 | Extreme value was recorded while Status was ON and EvPriority was non-zero; Source or Nominal input became NOT AVAILABLE while Status was OFF; Source or Nominal input became NOT AVAILABLE while Status was ON and EvPriority was zero. |
| Relative setpoint | * | Setpoint condition started; Setpoint condition ended; setup changes made while Setpoint was ON; module disabled while Setpoint was ON; Source or Nominal input became NOT AVAILABLE while Status was ON. |
* The priority of these events is define in the EVPriority setup register.
The Event output register stores the following information for each ION event: time stamp, priority, cause, effect, and any values or conditions associated with the cause and effect.
Detailed module operation
The diagram below describes the Relative Setpoint setpoint operation for a typical over setpoint condition. It also shows the events and the values that are recorded during the operation of the setpoint.
As shown in the diagram, the setpoint will change to an active state when the Source input exceeds the Over Pickup level for a period of time greater than SusUntlON. At this time, the Status and Over output registers change to on. Both registers return to off when the Source input falls below the Over Dropout level for a period of time greater than SusUntlOFF.
Similarly, if the Source input drops below the Under Pickup level for a period of time greater than SusUntlON, the Status and Under output registers change to on. Both registers return to off when the Source input exceeds the Under Dropout level for a period of time greater than SusUntlOFF.
NOTE: The determination of the Over Pickup level is shown on the right. The Over Dropout, Under Pickup and Under Dropout levels are determined in a similar way. Refer to this module’s setup register descriptions for details.
Pickup and Dropout Levels
The pickup and dropout levels shown in the diagram are determined by the value of the Nominal input in combination with the Eval Mode, Pickup and Dropout setup registers. The following shows how the over pickup level is determined:
- If Eval Mode is set to value, then the over pickup level is determined by adding the Nominal input to the value in the Pickup register. For example, if the Nominal input is a power reading of 200kW and the Over Pickup is set to 50kW, the setpoint will go active when the Source input exceeds 250kW.
- If Eval Mode is set to percentage, then the over pickup level is determined as a percentage of the Nominal input. For example, if the Nominal input is a power reading of 200kW and the Over Pickup is set to 50%, the setpoint will go active when the Source input exceeds 300kW (since this is 50% more than 200kW).
Event Timestamps
The Time 1, Time 2 and Time 3 points shown on the diagram are the timestamps for the three events produced by the Relative Setpoint module:
- The first event records the time (Time 1) at which the Status output register changes to on, and the value of the Source input when the greatest difference between the Source input and the over or under pickup level is attained, during the SusUntlON period.
- The second event records the time (Time 2) and the value of the Source input when the greatest difference between the Source input and the over or under pickup level is attained, while the setpoint is on.
- The third event records the time (Time 3) at which the Status output register changes to off, and the value of the Source input when the smallest difference between the source and nominal inputs is attained, during the SusUntlOFF period.
Disabling a Relative Setpoint
The Enable setup register determines if the Enable input controls the operation of the Relative Setpoint module:
Enable setup register disabled: the module is disabled.
Enable setup register enabled: the module operation is determined by the Enable input register.
You may want to enable or disable a Relative Setpoint module under different conditions. For example, you may have a Relative Setpoint set up to shed loads and you only want it enabled during times when a penalty tariff is in effect.
When the Enable input is off or the Enable setup is disabled, the Relative Setpoint does not evaluate the Source input and the Status, Over and Under output registers become not available.
Responses to special conditions
The following table summarizes how the module behaves under different conditions.
| Condition | Response of output registers |
|---|---|
| If either the Source or Nominal input is N/A | The Status, Over and Under output registers are N/A. |
| If the Enable setup is set to DISABLED or the Enable input is OFF | The Status, Over and Under output registers are N/A. |
| After the module is re-linked or its setup registers are changed | The Status, Over and Under output registers are OFF until the inputs are evaluated. |
| When the device is started or powered-up (either the first time, or after a shut-down) | The Status, Over and Under output registers are OFF until the inputs are evaluated. |