kitControl-LoopPoint
This component implements a simple PID control loop. Loop objects provide closed-loop PID control (proportional, integral, derivative) at the station level. Independent gain constants configure the loop as P-only, PI, or PID.
LoopPoint is available in the HVAC folder of the kitControl palette.
| Property | Value | Description |
|---|---|---|
| Facets | Config Facets window | Selects units and configures how the value displays: unit defines the unit of measure from acceleration to volumetric flow. precision defines the number of decimal places. min defines the lowest value allowed. max defines the highest value allowed. These facets apply to the Out value. |
| Out | read-only number | Displays the output value for the loop. |
| Loop Enable | true (default) or false and null definition | Turns the loop on and off. true enables the PID loop algorithm to execute at the rate selected by the Execute Time property. false forces the PID loop output to a value that is dependent on the selection in the Disable Action property. When null is checked, the value displayed defaults to the incoming value from the device.If you remove the check mark you can configure the In value. |
| Input Facets | Config Facets window | Selects units and configures how the value displays: unit defines the unit of measure from acceleration to volumetric flow. precision defines the number of decimal places. min defines the lowest value allowed. max defines the highest value allowed. These facets apply to the input. |
| Controller Variable | number (defaults to 0.0) and null definition | Defines the input value for the controlled property (for
example, space temperature). This input must be valid for this object
to function. When null is checked, the value displayed defaults to the incoming value from the device.If you remove the check mark you can configure the In value. |
| Setpoint | number of degrees of temperature and null definition | Defines the input value for the setpoint (for example, the
space temperature setpoint). This value must be valid for this object
to function. The object does not provide an integral command function
for the setpoint value when entered on the property sheet. If a commandable setpoint is required, link from a NumericWritable control point to the setpoint slot. |
| Execute Time | hours minutes seconds (defaults to .5 second) | Controls the execution frequency for the PID algorithm. |
| Actual Time | read-only integer (defaults to zero (0)) | Reports the milliseconds since the previous execution. Changing the Execute Time changes this time. |
| Loop Action | drop-down list (defaults to Direct) | Determines if the control algorithm is direct or reverse
acting. Direct increases the loop output as the value of the controlled variable increases to greater than the setpoint value. In a temperature loop, this is considered to be a cooling application. Reverse increases the loop output as the value of the controlled variable decreases to less than the setpoint value. In a temperature loop, this is considered to be a heating application. |
| Disable Action | drop-down list (defaults to Zero) | Selects the value for the loop output (Out) when Loop Enable is false. Max Value sets the loop output value to the value configured for Max Output. Min Value sets the loop output value to the value configured for Min Output. Hold maintains the loop output value at the last calculated value. Zero sets the loop output value to zero (0.00). |
| Tuning Facets | Config Facets window | Selects units and configures how the value displays: unit defines the unit of measure from acceleration to volumetric flow. precision defines the number of decimal places. min defines the lowest value allowed. max defines the highest value allowed. These facets apply to the tuning properties, such as the constants, Bias, and output properties. |
| Proportional Constant | number of seconds to three decimal places | Defines a value used by the loop algorithm to set the overall gain for the loop. A starting point for this value equals: output range/throttling range. |
| Integral Constant | number to three decimal places | Defines the integral gain in repeats per minute. The loop algorithm uses this value (also called the reset rate) to act on the magnitude of the setpoint error. A typical starting point is 0.5. |
| Derivative Constant | number to three decimal places | Defines the derivative gain used by the loop algorithm to act on the rate of change of the setpoint error. |
| Bias | number to two decimal places | Defines an amount of output the algorithm adds to correct any offset error. The algorithm uses this value normally only with proportional control. |
| Maximum Output | number to two decimal places | Defines the maximum output value that the loop algorithm can produce. |
| Minimum Output | number to two decimal places | Defines the minimum output value that the loop algorithm can produce. |
| Ramp Time | hours minutes seconds (defaults to 0) | Defines the minimum time that the output can ramp completely
from Minimum Output to Maximum Output, effectively establishing a rate-of-change slope. This component
enforces this value at station startup or whenever the LoopPoint transitions
from disabled to enabled. Once Ramp Time expires, it no longer affects the output. This property is intended to prevent the loop from opening a valve or other controlled device to its maximum limit (“slamming”) during startup. Note: The default
Ramp Time is 0:00:00, or disabled. To constrain the loop output rate
of change when the loop starts or is enabled, enter a reasonable Ramp Time value. |
Action
ResetIntegral clears the current integral component of the loop’s output calculation. If needed, you can link this slot to another object to provide a quick purge of the integral effect. Typically, the latter would provide more of a debug utility, and should not be necessary if the LoopPoint’s configuration properties are correctly defined.