Understanding Secondary Blocks

Secondary blocks manipulate data according to your instructions. Secondary blocks usually receive input from an upstream or primary block and perform a specific function with that input, such as perform a calculation or store several successive input values. Therefore, a secondary block cannot be the first block of a chain. However, you can connect secondary blocks to create a chain like the one shown in the following figure.

Chain Showing Secondary Blocks

Note that the first block in the chain is a primary block. This block is the primary source of data for the next block in the chain and determines the scan time for the entire chain. The following table lists the available standard secondary blocks.

Standard Secondary Blocks
The block...	Function:
Calculation (CA)	Performs mathematical calculations using values from the upstream block and up to seven other constants or block values.
Event Action (EV)	Monitors values or alarm conditions of the upstream block and performs actions based on the upstream block's output.
Extended Trend (ETR)	Allows you to collect up to 600 real-time values from an upstream block. You can display these values as a graph by adding charts to your pictures.
Fanout (FN)	Sends the value it receives from its upstream block to up to four additional blocks.
Signal Select (SS)	Samples up to six inputs, manipulating the inputs according to a user-selected mode, and outputs a value to the next block.
Timer (TM)	Counts time by incrementing or decrementing its value.
Totalizer (TT)	Maintains a floating-point total for values passed to it from upstream blocks. This block sends values up to six digits in precision to other blocks. It can display up to fifteen digits of precision in an operator display.
Trend (TR)	Allows you to collect up to 80 real-time values from an upstream block. You can display these values as a graph by adding charts to your pictures.

See Also