Change of Value Module

The Change of Value Module provides an efficient means of detecting a value that changes in the Virtual Processor. This module is only available in the VIP.

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Overview

Unlike a Setpoint module, the Change of Value Module performs its delta comparison relative to the last changed input value. One practical use is to trigger logging when a numeric or Boolean value, monitored at the Source input of this module, changes to a user-defined amount.

Inputs

Source

To monitor a change in an input value, link the input to the Source input. The value can be numeric or Boolean.

Enable

This input is optional; if you leave it unlinked, the module is enabled by default.

Setup registers

Delta

This register allows you to specify a value that is used to determine whether a change of value has occurred at the Source input. A delta value of 0.5 is interpreted as a Boolean transition (0 to 1 or 1 to 0).

Output registers

Last Value

When the value at the Source input has changed by an amount greater than the Delta setup register, the Last Value output register is updated with the current value at the Source input. The Last Value output register is what is used for comparison purposes.

Trigger

This output register pulses when the Last Value output register is updated. The Last Value register can be linked to a data recorder in conjunction with this Trigger output register to record data conditionally upon a change.

Event

Any events produced by the Change of Value Module are written into this register.

Possible events and their associated priority numbers are shown in the following table.

Event priority group	Priority	Description
Setup Change	10	Input links, setup registers or labels have changed.

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

When the module is first created and the Source input is linked, Last Value is populated with the first available value at the Source input. the Source input is constantly monitored and compared with Last Value. Assuming a numeric Source input, if Source changes by an amount greater than or equal to the Delta setup register:

• The Last Value output register is updated with the Source input value.
• The Trigger output register pulses.

If a Boolean Source input is used, the Delta setup register should be set to 0.5. This results in a change of value for any Boolean transition (0 to 1 or 1 to 0).

Responses to special conditions

Condition	Response of output registers
When the module goes online for the first time.	The Last Value output register is set to the first available Source input value until the Source input changes by the amount set in the Delta setup register.
When the Virtual Processor is started or powered up after a shutdown.	The Last Value output register retains the value it held at shutdown.
If the Source input is not available	The input is ignored for change evaluation.
After the module is relinked or its setup register changes.	The Last Value output register is set to the first available Source input value until the Source input changes by the amount set in the Delta setup register.