Spectrum Controls 1756sc-OF8H Series A - Manual (Page 13)

Preface xiii
are below the cut-off frequency are passed with under 3 dB of attenuation
for low-pass filters.
Channel Update Time -
dB (decibel) – A logarithmic measure of the ratio of two signal levels.
Digital filter - A low-pass mathmatic single order filter applied to the A/
D signal. The digital filter provides high-frequency noise rejection.
Effective resolution – The number of bits in the channel data word that
do not vary due to noise.
HART - Highway Addressable Remote Transducer
Local System - A control system with I/O chassis within several feet of
the processor.
LSB (least significant bit) – The bit that represents the smallest value
within a string of bits.
Multiplexer – A switching system that allows several input signals to
share a common A/D converter.
Normal mode rejection (differential mode rejection) – A logarithmic
measure, in dB, of a device’s ability to reject noise signals between or
among circuit signal conductors, but not between the equipment grounding
conductor or signal reference structure and the signal conductors.
Module update time – The amount of time that one data acquisition
cycle takes place and it reported to the PLC processor.
Remote system - A control system where the chassis can be located
several thousand feet from the processor chassis. Chassis communication
is via the 1756-CNB or 1756-ENET Adapter.
Resolution – The smallest detectable change in a measurement, typically
expressed in engineering units (e.g. 0.15 °C) or as a number of bits. For
example, a 12-bit system has 4096 possible output states. It can therefore
measure 1 part in 4096. See also effective resolution.
Sampling time - The time required by the A/D converter to sample an
input channel.