Watlow PPC-2000 - Manual (Page 316)

Glossary PPC-2000 User’s Guide
288 Watlow Anafaze Doc.# 30002-00 Rev 2.3
M
Manual Mode
A selectable mode that has no automatic control
aspects. The operator sets output levels.
Modbus
Industrial communications protocol developed by
AEG Schneider Automation.
Modbus Address
Number that specifies a bit or word register
within a controller’s memory.
Modbus Database Offset
A number which is combined with a parameter’s
first address to locate specific Modbus addresses.
Module
A component of a PPC-2000 system which
attaches and interfaces with other components.
Module I/O Number
Number designating each I/O supported on a
module. For example, a PPC-2021 has 16 analog
inputs; each input on the module has a unique
designation from 1 to 16.
O
Offset
The difference in temperature between the set-
point and the actual process temperature. Offset
is the error in the process variable that is typical
of proportional-only control.
Output
Control signal action in response to the difference
between setpoint and process variable.
Output Type
The form of PID control output, such as Time
Proportioning, Distributed Zero Crossing,
SDAC, or Analog. Also the description of the
electrical hardware that makes up the output.
P
Parameters
The programmed instructions and readings that
are stored in a microprocessor software.
Parity
A communications error checking method in
which the quantity of bits in each byte is deter-
mined to be odd or even. If there is a discrepancy
between the transmitter and receiver, a communi-
cations error has occurred.
PID
Proportional, Integral, Derivative. A control
mode with three functions: Proportional action
dampens the system response, Integral corrects
for droops, and Derivative prevents overshoot
and undershoot.
Pin Number
Generic terminal block identification numbers
which are correlated to module I/O numbers in
terminal block identification tables for wiring.
Polarity
The electrical quality of having two opposite
poles, one positive and one negative. Polarity
determines the direction in which a current tends
to flow.
Process Variable
The parameter that is controlled or measured.
Typical examples are temperature, relative
humidity, pressure, flow, fluid level, events, etc.
The high process variable is the highest value of
the process range, expressed in engineering units.
The low process variable is the lowest value of
the process range.
Proportional (P)
Output effort proportional to the error from set-
point. For example, if the proportional band is
20
º and the process is 10 º below the setpoint, the
heat proportioned effort is 50%. The lower the
PB value, the higher the gain.
Proportional Band (PB)
A range in which the proportioning function of
the control is active. Expressed in units, degrees
or percent of span.
See PID.
Proportional Control
A control using only the P (proportional) value of
PID control.