Lake Shore 350, Руководство пользователя

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4.5.1 Heater Outputs 81
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Most applications require control in units of temperature. To control in units of tem-
perature, set the Preferred Units parameter of the control input sensor to either kel-
vin or Celsius. When controlling in temperature, the available setting range of the
setpoint is limited by the Setpoint Limit parameter of the assigned temperature
curve. Refer to section 4.4.12 for details on setting the Preferred Units parameter.
Refer to section 5.8.1 for details on setting a curve Setpoint Limit.
The Setpoint Limit feature only limits the Setpoint entry. For even greater protection, the
Temperature Limit feature can be used to turn off all heater outputs if a sensor reading
above the specified temperature is observed. Refer to section 4.4.11 for details on the
Temperature Limit feature.
There are some instances when temperature control in sensor units may be desired,
for example when a temperature curve is not available. For these applications the
Model 350 can control temperature in sensor units. To control in sensor units, set the
Preferred Units parameter to Sensor. When controlling in sensor units, the Setpoint
resolution matches the display resolution for the sensor input type given in the speci-
fications (section 1.6.1).
Temperature control in sensor units can be unpredictable since most sensors do not have
a linear response to temperature, and therefore have can have different sensitivity in dif-
ferent temperature ranges.
If you change the Preferred Units from Sensor to temperature (Kelvin or Celsius), or
from temperature to Sensor, the Model 350 uses the assigned temperature curve to
convert the Setpoint to the new control units. This provides minimal disruption in the
control output if you change the Preferred Units parameter while the control loop is
active.
Menu Navigation:
Setpoint
Q
(See note below)
Default: 0.0000 K
Interface Command:
SETP
When controlling in temperature, setpoint is limited by the control input temperature
curve’s Setpoint Limit. When controlling in sensor units, setpoint is limited by the limits of
the configured control sensor.
4.5.1.5.7 Setpoint Ramping
The Model 350 can generate a smooth setpoint ramp when the setpoint units are
expressed in temperature. You can set a ramp rate in degrees per minute with a range
of 0 to 100 and a resolution of 0.1. Once the ramping feature is turned on, its action is
initiated by a setpoint change. When you enter a new setpoint the instrument
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.
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 I contribution of the control output
equation to become larger the longer the error exists. This will result in a large over-
shoot or undershoot once the setpoint temperature is reached, since the I contribu-
tion 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.