Spectrum Controls 1756sc-IF8u - Manual (Page 7)

Preface
vii
Cut-off frequency - The frequency at which the input signal is attenuated
3 dB by the digital filter. Frequency components of the input signal that
are below the cut-off frequency are passed with under 3 dB of attenuation
for low-pass filters.
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.
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.
Mulitplexer – 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 – See channel update time.
Remote system - A control system where the chassis can be located
several thousand feet from the processor chassis. Chassis communication
is via the 1756-DHRIO and 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.
RTD (Resistance Temperature Detector) - A temperature sensing
element with 2, 3, 4, lead wires. It uses the basic characteristics that
electrical resistance of metals increases with temperature. When a small
current is applied to the RTD, it creates a voltage that varies with
temperature. This voltage is processed and converted by the RTD module
into a temperature value.
Sampling time - The time required by the A/D converter to sample an
input channel.