LTCH (Latch) - Metasys - LIT-12011942 - "" - Software Application - Metasys Open Data Server - 10.1

Metasys Open Data Server Help
Product
Building Automation Systems > Databases and Data Servers > Metasys Open Data Server
Document type
User Guide
Document number
LIT-12011942
Version
10.1
Revision date
2019-10-14

The Latch block holds a binary value until you command it to reset. Latch blocks help capture rapidly changing binary states that might otherwise be missed. The Input of the Latch block is a binary attribute, sampled every time the logic system runs (every 5 seconds). Use an Attribute Reference block to create the Input for Latch.

Reset determines if the Output of the block changes with a change in the value of the Input. When Reset is True, the Output of the Latch block stays its original value, even if the Input changes value. Reset is also a binary attribute. To change the value of Reset, double-click the binary attribute block in View Mode and issue an Inactive or Active command.

This table translates the value of the Input or Reset binary attribute into True and False values for the Latch block:

Table 1. Latch Blocks

Binary Attribute Value

Command/State

True or False

1.0

Active

True

0.0

Inactive

False

The following table and figure summarize the operation of the Latch block:

Table 2. Latch Block Operation

Input

Reset

Output

Goes from False to True

False

True

Even if the Input goes to False, the Output stays True as long as Reset is False.

Goes from False to True

True

False

Goes from True to False

False

True

Even if the Input goes to True, the Output stays False as long as Reset is False.

Goes from True to False

True

False
Figure 1. Latch Block Example