Lake Shore 372, Руководство пользователя, Страница: 110 / 214

98 c
HAPTER
4: Operation
Model 372 AC Resistance Bridge and Temperature Controller
4.6.1.5.7 Setpoint Ramping
The Model 372 can generate a smooth setpoint ramp when the preferred units are
expressed in temperature. You can set a ramp rate in degrees kelvin per minute with a
range of 0 to 100 and a resolution of 0.001. Once the ramping feature is turned on, its
action is initiated by a setpoint change. When you enter a new setpoint the instru-
ment changes the setpoint temperature from the old value to the new value at the
ramp rate. A positive ramp rate is always entered; it is used by the instrument to ramp
either up or down in temperature. When you enter a ramp rate of zero, the setpoint
change will be instantaneous, despite the setpoint ramping feature remaining on.
This is most useful in zone control mode, when you desire ramping to be enabled for a
particular output, but not necessarily for all zones.
Always use the ramping feature to minimize temperature overshoot and undershoot.
When ramping is not used, a setpoint change can cause the error used by the PID
equation to become very large, which causes the integral contribution of the control
output equation to become larger the longer the error exists. This will result in a large
overshoot or undershoot once the setpoint temperature is reached, since the integral
contribution will only decrease when the error polarity is reversed. Use a ramp rate
that keeps the control output from reaching the extremes of 100% or 0% while
ramping for optimal results
The ramping feature is useful by itself, but it is even more powerful when used with
other features. Setpoint ramps are often used with zone control mode. As tempera-
ture is ramped through different temperature zones, control parameters are auto-
matically selected for best control. Ramps can be initiated and status read back using
a computer interface. During computer-controlled experiments, the instrument gen-
erates the setpoint ramp while the computer is busy taking necessary data.
When an incomplete ramp is shut off, the setpoint will remain on the most current setting
(the reading will not jump to the end of the ramp).
If the input type or input curve is changed while a ramp is in progress, both ramping and
the heater are turned off.
If Ramp is on and the setpoint is set to sensor units, the ramping function will remain on
but when another setpoint is entered, the setpoint goes directly to the new setpoint
value.
To bypass ramping and load the setpoint with the current temperature, with the control
loop displayed, press and hold the Setpoint button for 3 s.
Menu navigation:
Output Setup
Q
Sample Heater or Warm Up Heater
Q
Setpoint Ramping
Q
(Off or On)
Default: Off
Interface command:
RAMP
To stop a ramp, when the desired control loop is displayed, press Setpoint , then
immediately press Enter . This stops the ramp at the current setpoint, but leaves the
ramping function activated. To continue the ramp, enter a new setpoint. Refer to sec-
tion 4.6.1.5.6 for details on setting the setpoint parameter.