ALLEN BRADLEY 1747-L551 PLC Processor

Glossary
GL–5
Signal Delay — For inputs, the response time required to transmit
the circuit status from the field wiring to the digital logic. For
outputs, the time required to transmit the circuit status from digital
logic to the output wiring.
Sinking — A term used to describe current flow between an I/O
device and SLC I/O circuit — typically, a sinking device or circuit
provides a path to ground, low, or negative side of power supply.
Sinking/Sourcing — Describes a current signal flow relationship
between field input and output devices in a control system and their
power supply. Sourcing I/O modules supply (or source) current to
sinking field devices. Sinking I/O modules receive (or sink) current
from sourcing field devices.
Sourcing — A term used to describe current flow between an I/O
device and SLC I/O circuit — typically, a sourcing device or circuit
provides a path to the source, high, or positive side of power supply.
Strobe Message — A strobe message is a multicast transfer of data
sent by the scanner that solicits a response from each slave device.
The devices respond with their data.
Surge Current Per Point — The maximum amplitude and duration
(pulse) of current allowed for a given period of time and
temperature.
Surge Suppressor — A device used to absorb voltage transients
created by energizing an inductive load to reduce electrical noise or
to protect the output circuit. For example, an R-C network, MOV
(metal oxide varistor) or diode.
Token — The logical right to initiate communications. In a
multi-master network a single token is passed between initiators to
make sure two nodes do not transmit at the same time.
UVPROM — An Ultra-Violet light erasable Programmable Read
Only Memory module used to back-up, store, or transfer SLC 500
programs. The SLC 5/01 and SLC 5/02 can only read from a
UVPROM. An external PROM programmer is used to program
(write to) the device.
Voltage Category — The nominal voltage used to describe the
module.
Watts Per Point — The maximum heat dissipation that can occur in
each field wiring point when energized.
Publication 1747-6.2