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.

Figure 58. LoopPoint properties

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.