Logical Relationships

A logical relationship is an association between two assets that isn't physically obvious - for example, it doesn't have a pipe, cable or chain connecting the two.

Logical relationships are quite open - you can make a new logical relationship to represent a wide number of different types of association.

A few examples appear below…

Name: Control

Upstream Name: Controlled By

Downstream Name: Controls

This relationship indicates a control relationship between assets. A control loop is formed when you have three assets working together to regulate a measurement - for example, a temperature sensor, a temperature controller and a burner are all used to regulate the temperature of water in a boiler.

In this case, the sensor controls the controller, which in turn controls the burner.

However, the physical relationships between these items may be far more complex - for example, before it reaches the temperature controller, the signal from the sensor may pass through a converter, a display and a PLC - or it could be networked, running through a large amount of network infrastructure before it finally arrives at the controller.

Having the 'Controls' relationship streamlines the whole process - regardless of the physical connections, the user is immediately advised what the asset they are looking at controls and/or is controlled by.

The burner is controlled by the temperature sensor

The temperature sensor controls the burner.

Name: Configured

Upstream Name: Configured By

Downstream Name: Configures

There are many assets that have specific tools that are unique only to that type of device. This is particularly common smaller, low-cost programmable devices.

The 'Configured' relationship associates the asset with the tool that needs to be used to configure it. The relationship isn't physical because the two items aren't attached 99% of the time - however, it's a vital piece of information to know.

The temperature sensor is configured by the programming kit

The programming kit configures the temperature sensor.

Name: Startup Sequence

Upstream Name: Operates Before

Downstream Name: After

Startup and shutdown sequences for many plants are complicated, with a diverse range of equipment operating in what is sometimes a very rapid progression. However, they must follow a rigidly defined sequence of operation in order to not cause damage to the system as a whole.

A 'Sequence' logical relationship associates your assets in the order that the sequence should appear.

These relationships are also very useful when creating charts.

The pump is after the priming system

The priming system operates before the pump.