Issue
Some issues which this article covers are:
- What rules or recommendations should be used with Indirect and Global Points?
- Why might a global point not change?
- Attempting to alter a global AO/DO points' value/state, by "Point Control" without "Manual Mode" being used, and the change does not take place. (Referred to as Global Output Retentive Feedback.)
- What scan rates should be used for global / indirect points?
Product Line
TAC INET
Environment
I/NET Software
Cause
Often within a system, a point's status or value within one controller has to be shared or used in other controllers connected to the system. An example could be an outside air temperature sensor connected to a controller. The value of the outside air temperature in that controller can be transmitted across the I/NET network to be used in algorithms in the other controllers.
The I/NET software and firmware provides the mechanism to transmit and receive point data system wide. The outside air temperature point in this example would be called a "global point." The receiving points within the other controllers that reference and thereby mimic the global point's temperature value are called "indirect points."
Resolution
Each controller is capable of a total of 128 global and indirect points.
Global points are used to share information from one controller to another. If a point is not a global point, the state or value of that point is available only to other points in the same controller. If a point is specified as global, you may use it to control an indirect point in another controller. Any internal or external point may be designated as a global point.
When a point is defined as global, a corresponding indirect point must be set up in the additional controller(s) to receive the global point's data. The global point must be designated with the appropriate globalisation level.
There are four (4) different levels of globalisation, as shown below:
- Local: This point provides information only to this controller. A global setting of "Local" indicates that this point is not a global point.
- LAN: This point may provide information to an indirect point in any device connected to this controller LAN.
- Link: This point may provide information to an indirect point in any device connected to this controller's Host LAN. This setting WILL NOT send global data across links headed by NetPlus Routers.
- System: This point may provide information to an indirect point in any device connected to the I/NET system including ETHERNET. This setting WILL send global data across links headed by NetPlus Routers.
Global points "broadcast" or send their state/value to corresponding indirect points. The frequency of the broadcast depends on the point type.
All global point types broadcast under the following conditions:
- The controller has been restarted, either by a power restore, the controller's red reset button has been pushed or the database, DCU0000.sav file, has been "Restored."
- A global point has been changed from "Automatic" to "Manual" or from "Manual" to "Automatic." This does not apply to the Test Mode.
- A global point changing to or recovering from the "old data" state due to either a communications failure, or an analogue input point falling outside or re-entering its sensor limits (defined within the 'Resident Points' editor).
- Global analogue points (AI, AO, GI, GO) broadcast whenever their value changes through a range greater than the specified "Broadcast change counts" parameter (defined within the 'Resident Points' editor).
- Global discrete points (DI, DA, DO, DM, DC) broadcast whenever their state changes.
- Global pulsed input points (PI) broadcast whenever their "Scans between broadcasts" parameter is exceeded (defined within the 'Resident Points' editor).
- When requested to by the associated indirect point.
Indirect points "receive" their state/value from their corresponding global points. Indirect points must reside in a different controller from the global point, and they act as receptors for the value or status information broadcast from the global point.
When entering an indirect point, you must specify the name or address of the associated global point. The frequency of the update from the global points depends on the following.
- Their associated global point broadcasting its status or value.
- In addition, an indirect point can request an update, at the indirect points scan rate, from their associated global point. This happens when:
- The indirect point is first entered.
- When the indirect point's controller is restored or reset (power restore, station restore or the red reset button is pressed).
- Whenever the local control LAN reconfigures.
- Whenever an AO or DO indirect point is put into "Manual Mode" or back into "Automatic Mode."
- When the indirect point has not seen a status/value change from its associated global point within 2 times the indirect point's scan interval it request an update from its associated global point. It then reports the update on its third scan interval. If the indirect point is unable to be updated from its global point (i.e. no communications) then the indirect point will report its last valid updated value/state and will flag the value/state as "Old Data."
Direction of Point Data's Flow
INPUT POINTS
- (AI, GI, DI and DA): The data flow is from the global input point broadcasting to the associated indirect point only. The flow is "one way" only, that is to say, if the associated indirect point should alter the state or value is not broadcast to their corresponding global point.
GLOBAL INPUT --------------> LAN -------------> INDIRECT INPUT
OUTPUT POINTS
- (AO, GO and DO): All output points (both global and indirect) broadcast their state or value changes to the other associated point(s). The flow is "two way," that is to say, a change to either the global or the associated indirect point will change their opposing point's value accordingly.
GLOBAL OUTPUT <--------------> LAN <----------------> INDIRECT OUTPUT
Click Here to view some recommendations / rules for Global and Indirect Points as well to view this complete article as one document.
