Print this page

Intelligent Temperature Controller

Relay Rules.

The configuration for the temperature controller is handled by rules set up in the 'strings' portion of either the SNMP MIB, or in the SiteMonitor Manager application. These rules are rather simple to implement, and are described below:

A rule consists of multiple 'terms' which are each separated by '&'. For instance, a rule could be something like "A>23&A<B&NOT1". This rule has three terms - A>23, A<B, and NOT1. All three of these terms have to be true for the relay to be activated.

There are only a limited number of terms available, which are described below:

Temperature setpoint terms. These are in the form of a temperature input letter (A or B), followed by a greater than (>) or less than (<) symbol, and then a numberic temperature in celsius. Some examples: A<5, means turn the relay on whenever temperature A is less than 5*C. B>23 means turn the relay on when temperature B is more than 23 degrees celsius. There are only four possibly rules in this category - basically A>#, A<#, B>#, and B<#.

Temperature comparison terms. These are used to permit the operation only when the temperature of one of the sensors is higher or lower than the other one. There are only two rules in this category, A>B, and A<B. A>B means operate the relay only when temperature A is higher than temperature B. A<B works similary except B must be higher than A. An example application of the rules in this category is where you want to ensure that a ventilation fan is not turned on if the outside temperature is hotter than the inside temperature.

Interlock terms. These rules are used to prevent the simultaneous engagement of two relays, where this operation is not desired. For instance, heating and cooling at the same time. These rules are in the form of "NOT#" where # is a relay number. Adding a NOT term to a relay rule means that this relay will not be activated if the relay with the number included in the term is activated. For instance, adding NOT2, means don't turn this relay on if relay 2 is activated. Two things should be noted at this point: First, even relays which are interlocked in this way can be on at the same time for a brief period, due to the way the software operates internally. Second, it is not wise to create interlocking loops - for instance where relay 1 has a NOT2 term included, and relay 2 has a NOT1 term. This can cause interesting interactions and may prevent proper operation of the system.