Nextron MASTERTRACE MS-2101, Руководство оператора

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1.5
MS-2101 Chapter 1 Product Overview
Cycle modulating the current through the heater has the
effect of turning the heater on and off rapidly and
therefore, power output is reduced in the long run. Since
the switching is zero-cross controlled, the controller
knows exactly when power cycles start and finish. Zero-
cross switching also helps reduce power harmonics that
generate unnecessary interference.
The heater current (average current) measured by the
controller while cycle modulation is in effect may be
approximated as follows:
Heater Current at 100% x Duty Cycle = Average Current
When powerlimit is enabled, a powerlimit current is set
by the user. This is essentially the desired average current.
The powerlimit control algorithm ensures that the actual
current will not exceed the powerlimit setting while
optimizing the maximum duty cycle possible. When the
average current exceeds the powerlimit setting, the duty
cycle is reduce by 10%. When the average current is
below the powerlimit setting, the duty cycle is increased
by 10%. Before the algorithm increases or decreases the
duty cycle, the controller waits until the heater current has
reached steady-state at the current duty cycle setting. If
the heater is initially off and the controller calls for heat,
the duty cycle starts at zero and increases by 10%
increments until it reaches a steady-state value. This
ramping up effect provides a current-driven softstart
whenever the controller calls for heat unlike the softstart
function, which is time driven.
Softstart
During cold temperature startups with self-regulating heat
trace cables, the current driven softstart built into the
powerlimit function may not be long enough to overcome
the inrush current. The softstart function is separate from
powerlimit and is time driven where for when you set the
softstart period. Having the two separate functions is
desirable when powerlimit may not be required by the
application but softstart is essential to avoid nuisance
breaker trips during cold startups. The controller applies
the softstart function initial startup when the controller is
powered up.
Operation of the softstart function varies depending on
whether or not powerlimit and/or proportional control are
enabled. When powerlimit and proportional control are
off, operation is simplified. The softstart function uses
cycle modulation to gradually increase power output over
the softstart period. Since most circuit breakers are the
thermal type, the cycle modulated output appears as a
reduced load to the circuit breaker.
During controller power-up and assuming the controller is
calling for heat, the duty cycle starts at 10% and incre-
ments by 10% until full power is reached. Since there are
ten duty cycle increments, the time that the controller
maintains each duty cycle setting is the softstart setting
(softstart period) divided by 10. The softstart operation
powerlimit and proportional control off is shown by the
curve in figure 1.3.
Figure 1.3 Softstart Curve with Powerlimit and
Proportional Control Disabled
With powerlimit enabled, the only difference is that
instead of the duty cycle ramping to 100%, it stops at the
value determined by the powerlimit function such that the
average current does not exceed the powerlimit current
set by the user. The maximum duty cycle setting is
approximated by the controller initially so that the time
period for each duty cycle increment can be determined.
The softstart operation with powerlimit enable is shown
by the curve in figure 1.4.
Figure 1.4 Softstart Curve with Powerlimit Enabled
When proportional control is turned on, the maximum
duty cycle available to the controller is constrained by the
powerlimit current if enabled and softstart.