Analog Output (Std. with Feedback)

Owned by Gary Cane
May 09, 2022


Operator Menu Location: Generic Hardware Operators Analog Outputs


Operator Bitmap:


Functional Description:
The Standard Analog Output with Feedback generic hardware operator provides access to an analog output channel resource in the physical hardware. Feedback is provided by a dedicated analog input channel resource associated with the output resource.


When the generic operator is linked to a specific hardware resource, the operator commands that hardware resource to generate a physical signal corresponding to its input (provided that its enable digital input x2 is HIGH; when x2 is LOW the hardware output resource is turned off).


The operator can treat the input value as the raw signal value to reproduce, in the unit of measure defined by the hardware configuration (e.g., 4-20mA, 0-10V, etc.) For example, if , the operator will generate a 4V signal when the hardware is configured for 0-5V operation. It will also produce a 4V signal if the hardware range is configured 0-10V operation. And it will generate 4mA signal if the hardware range is set to 4-20mA mode.


Alternatively, the operator can be configured to automatically map the input value from a user-defined range to the configured physical signal range, as follows

Here, AO is the output signal value to be generated by the physical hardware resource, is the operator's command input value, and represent the hardware configuration's raw signal range (e.g., mA, mA), is the user-defined value corresponding to , and is the user-defined value corresponding to . For example, suppose the hardware is configured for 4-20mA operation such that mA, mA, and the corresponding user-configured range is set to and . Then, if the command input was , the physical output will be AO=12mA.

The operator output y1 is a feedback signal---a measurement of the actual output value that is generated by the hardware. Output y1 can be configured to simply provide the raw feedback signal value (unscaled), or it can automatically map the feedback signal to a user-defined range:

Here, fb is the feedback signal in the unit of measure that the hardware is configured for, and represent the nominal range for the raw feedback signal, (e.g., mA, mA), is the user-defined value corresponding to , and is the user-defined value corresponding to .
The purpose of the feedback signal is to ascertain that the hardware circuitry is correctly generating the command input. Deviation from the command input could be used to signal a system fault (e.g., hardware failure, wiring problem, etc..) If the output resource is redundantly wired to an actuator (i.e., another output resource is wired in parallel to the same actuator), the feedback signal represents a measurement of the output command to the actuator (regardless of which resource is driving that actuator).
Error output is HIGH when a feedback error occurs and LOW otherwise. A feedback error occurs when the output is turned on (i.e., =HIGH) and the feedback signal deviates from the commanded output signal for a sustained period of time. (The feedback signal is said to deviate from the command signal if the difference between the two exceeds a user-specified tolerance. The deviation time period is also a user-specified setting.) Once an error condition is flagged, the error will not be cleared until the command output matches the feedback signal for a user-specified period of time. (The feedback signal is said to match the command signal if the difference between the two is less than this tolerance setting.)


User-Defined Properties:
Object Name. A string label that identifies the operator
AO Scale. Either Hardware Defined or User Defined. In Hardware Defined mode, operator generates output to match input value in the unit of measure defined by the hardware configuration. In User Defined mode, maps the input value within user-defined scaling range to the physical signal range .

AO Lo-Range Scaled Equivalent. The input signal value corresponding to the low end of the physical signal range that the output is to generate when User Defined mode is selected
AO Hi-Range Scaled Equivalent. The input signal value corresponding to the high end of the physical signal range that the output is to generate when User Defined mode is selected

Units. Engineering units label used for readability.

AI Scale. Scaling mode for analog input feedback---either Hardware Defined or User Defined. In Hardware Defined mode, provides the raw feedback signal value in the unit of measure defined by the hardware configuration. In User Defined mode, maps raw feedback signal to user-defined scaling range.

AI Lo-Range Scaled Equivalent. The operator representation of the feedback signal at the low end of the hardware range when User Defined mode is selected


AI Hi-Range Scaled Equivalent. The operator representation of the feedback signal at the high end of the hardware range when User Defined mode is selected

Max Allowable FB Deviation. Maximum difference between commanded output value and feedback signal in absolute units. If difference is exceeded for sustained period, fault condition is reported on output .

Set Error Hysteresis Time. Amount of time in seconds that output command signal must deviate from feedback signal before error is reported on output .

Clear Error Hysteresis Time. Amount of time in seconds that output command signal must agree with feedback signal before error is cleared on output .

Display Switch Input. Determines if input pin is displayed on the screen. The pin must be displayed if a virtual signal wire is connected to it.

Display Feedback Output. Determines if output pin is displayed on the screen. The pin must be displayed if a virtual signal wire is connected to it.

Display Error Output. Determines if output pin is displayed on the screen. The pin must be displayed if a virtual signal wire is connected to it.


Comments:
•The value may be greater than the value.
•If input is outside of the user-defined range , the physical output signal may also be outside of the hardware configuration range . For example, suppose the user-defined AO mappings are set to 0 and 100 and the hardware resource is configured as a 4-20mA output. If , the operator will command the hardware to generate an output of 21.6mA (substitute , mA, mA, , and mA into the equation above). Note that the hardware output may not be able to reproduce the commanded output (depending on the hardware implementation, it may saturate at some value between 20mA and 21.6mA).
•The value may be greater than the value.
•If the feedback signal is outside of the nominal hardware range, the operator representation may be outside of the user-defined range. For example, suppose the user-defined mappings are set to 0 and 100 and the hardware resource is configured for 4-20mA signals. A reading of 0mA, will be mapped to -25 (substitute fb=0, , , mA, and mA into the equation above.


See Also:
Analog Output (Standard), Analog Input (Standard)