46
On/Off Output Type
In a heating application, the controller applies 100% output power if the
process temperature is below the setpoint and 0% at the setpoint. For a
cooling application, the controller applies 100% output power if the process
temperature is above the setpoint and 0% output power at the setpoint.
There are only two output states: fully on and fully off.
Applications for On/Off Control: 1. When temperature oscillation is
acceptable. 2. When constant cycling of mechanical devices is prohibited
(compressors, blowers, etc.). 3. Under-powered processes.
Output Low Limit %
Prohibits the controller’s output from going below the specified percentage.
Output High Limit %
Prohibits the controller’s output from going above the specified percentage.
Output Relay
Relays that are normally driven by the alarm output condition but can, as an
alternative, be driven by segments of the program.
PID Output Type
(Proportional -
Integral-Derivative)
The controller modulates output power by adjusting the output power
percentage within a proportional band. Power is proportionally reduced as
the process temperature gets closer to the setpoint temperature. PID
control helps reduce overshoot on start-up, enhances stability, and
compensates for process lag. The PID parameters are automatically
calculated for a particular application during the autotune process.
Applications for PID Control: 1. Where process temperature lags exist. 2.
When load changes are present. 3. When overshoot is prohibited. 4. When
very accurate control is required.
Program
A preset profile of the controller setpoint made up of ramps and soaks,
together with the sequence of state of the output relays.
Proportional Action
The lower the gain value (large proportional band) the less reactive the
output becomes proportionally to the error between setpoint and process
value. The proportional band is the range of process value over which this
linear gain action occurs before the output saturates at maximum or
minimum. This is often expressed as a percentage of the instrument span.
The gain of the instrument varies inversely as the proportional band
increases. (see Manual Reset)
Proportional Band
The band (expressed in degrees of temperature) in which the controller
modulates its power percentage.
Ramp
One segment of a program where the controller setpoint moves from one
level to another linearly during a fixed period of time.
Reset
An action which returns a completed or running program to the start
condition, i.e. controlling SP1, SP2, or remote SP.
Reverse Action
Control action such that the output decreases as the process value
increases.
Run
An action which starts a program running or restarts it from a hold condition.
Summary of Contents for M2B
Page 1: ... Rev A ...
Page 49: ...48 ...
