Carrier 19XL - Manual (Page 51)

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Definitions
Analog Signal
An analog signal varies in proportion to the monitored source. It quantifies values between
operating limits. (Example: A temperature sensor is an analog device because its resistance
changes in proportion to the temperature, generating many values.)
Digital Signal
A digital (discrete) signal is a 2-position representation of the value of a monitored source.
(Example: A switch is a digital device because it only indicates whether a value is above or
below a set point or boundary by generating an on/off, high/low, or open/closed signal.)
Volatile Memory
Volatile memory is memory incapable of being sustained if power is lost and subsequently
restored.
CAUTION CAUTION !
The memory of the PSIO and LID modules are volatile. If the battery in a module
is removed or damaged, all programming will be lost.