Varec TankGate Interface 8315 Series User Manual

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8300

8315 L&J Tankway Software Description

4.4

Gathering Point Data

For Host to TankGate communications, there are two primary methods for gathering 

point data. These methods are listed below:

The Host issues scan requests, and the TankGate responds with the data. 

The Scan method has the advantage of being deterministic, the response time to a 

particular request will always be the same.

This method has the limitation that if there are many points defined in the TankGate, it 

often takes several requests to obtain all of the data. Most of the time data has not 

changed since the last request, so this results in inefficiencies in update times. This 

situation is often the case in systems where there are many digital points that do not 

change frequently.

The Host issues scan requests based on a Change of State condition. Some systems refer 

to this as Event Mode. The TankGate keeps track of the items that have changed since 

the last Host request. The Host can issue a single request of ‘tell me what has changed 

since my last request.’ The TankGate will respond with the results, which include 

addressing information about the data. In a typical system, this results in a significant 

improvement in the throughput rate for data.

When FuelsManager is the Host system, the Change of State method has the advantage 

of being very efficient. Only the data that has changed is reported. Change of State is 

not available when using Modbus.

In order to support the Change of State method, many points have additional 

configuration parameters included. 

Parameter

Description

Value

One of the parameters which will be returned to a Change of State request by 

the Host. Most Software Blocks are designed so that the Value parameter is 

the main parameter of interest.

Report

Is used for Change of State processing only
Causes automatic notification to the Host (in response to a Change of State 

Request) when the Value Changes State.
Valid values are High, Low or No. Report=No disables notification.
Points with Report = High have higher priority than points with Report = 

Low.

Maxtime

Is used for Change of State processing only
Specifies the maximum time (in secs) between automatic Change of State 

data being sent to the Host in response to a Change of State Request.
When the Maxtime period expires, the Value to is forced appear as if it has 

changed even if is has not, ensuring that data is sent to the host periodically.
Setting Maxtime to 0 disables this option. The maximum is 255 seconds.