Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B - Manual (Page 400)

Publication 900-UM007D-EN-E - January 2011
D-2 Glossary
Contact Output: Relay control outputs are often available in these contact
forms:
• Form A Contact (SPST-NO): Single-pole, single-throw relays use the
normally open and common contacts to switch power. The contacts
close when the relay coil is energized and open when power is removed
from the coil.
• Form B Contact (SPST-NC): Single-pole, single-throw relays use the
normally closed and common contacts. These contacts open when the
relay coil is energized and close when power is removed from the coil.
• Form C Contact (SPDT): Single-pole, double-throw relays use the
normally open, normally closed, and common contacts. The relay can
be wired as a Form A or Form B contact.
Control Action: The control output response relative to the difference
between the process variable and the set point. For reverse action (usually
heating), as the process decreases below the set point, the output increases. For
direct action (usually cooling), as the process increases above the set point, the
output increases.
Control Mode: The type of control action used by the controller can include
ON/OFF, time-proportioning, PD, and PID. Other combinations and
refinements are used.
CSA: Canadian Standards Association is an independent testing laboratory
that establishes commercial and industrial standards, as well as tests products
and certifies them.
C-UL: This symbol appearing in literature and marked on products indicates
Canadian recognition of Underwriters Laboratories, Inc. approval of particular
product classes. The C-UL approval may stand in place of Canadian Standards
Association certification. All references to C-UL are based on prior listing or
recognition from the original UL file.
Dead Band: The time period in a control system between a change in stimuli
and any measurable response in the controlled variable. In the deadband,
specific conditions can be placed on control output actions. Operators select
the dead band width. It is usually above the heating proportional band and
below the cooling proportional band.
Derivative: The rate of change in a process variable which forms the “D” in a
PID control algorithm. This control action anticipates the rate of change of
the process and compensates to minimize overshoot and undershoot.
Derivative control is an instantaneous change of the control output in the
same direction as the proportional error. This is caused by a change in the
process variable (PV) that decreases over the derivative time.