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Handbook of air conditioning and refrigeration / Shan K

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5.24 CHAPTER FIVE<br />

Universal analog<br />

inputs;<br />

Fully integrated<br />

output relays,<br />

overrides <strong>and</strong><br />

transducers;<br />

Wireway space<br />

Independent power<br />

supplies for each<br />

electronic module;<br />

Tool-less installation;<br />

Onboard diagnostic<br />

displays <strong>and</strong> indications.<br />

Context-sensitive<br />

touchpad;<br />

user interface.<br />

FIGURE 5.13 A typical system controller. (Source: Johnson Controls. Reprinted by permission.)<br />

● R<strong>and</strong>om-access memory (RAM), which stores custom control s<strong>of</strong>tware developed during installation<br />

or prepared by the user. This type <strong>of</strong> memory is volatile (i.e., it can be read from <strong>and</strong> written to)<br />

<strong>and</strong> requires battery backup.<br />

● Electric erasable programmable read-only memory (EEPROM), which stores custom control s<strong>of</strong>tware<br />

<strong>and</strong> is volatile. The advantage <strong>of</strong> EEPROM over RAM is that EEPROM does not need

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