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Temperature Control
The Model 325 temperature controller
off ers two independent proportional-
integral-derivative (PID) control loops.
A PID algorithm calculates control output
based on temperature setpoint and
feedback from the control sensor. Wide
tuning parameters accommodate most
cryogenic cooling systems and many
small high-temperature ovens. A high-
resolution digital-to-analog converter
generates a smooth control output.
The user can set the PID values or the
Autotuning feature of the Model 325 can
automate the tuning process.
Control loop 1 heater output for the
Model 325 is a well-regulated variable DC
current source. The output can provide
up to 25 W of continuous power to a
50 Ω or 25 Ω heater load, and includes a
lower range for systems with less cooling
power. Control loop 2 heater output
is a single-range, variable DC voltage
source. The output can source up to 0.2 A,
providing 2 W of heater power at the
50 Ω setting or 1 W at the 25 Ω setting.
When not being used for temperature
control, the loop 2 heater output can be
used as a manually controlled voltage
source. The output voltage can vary from
0 to 10 V on the 50 Ω setting, or 0 to 5 V
on the 25 Ω setting. Both heater outputs
are referenced to chassis ground.
The setpoint ramp feature allows smooth
continuous setpoint changes and can
also make the approach to setpoint
more predictable. The zone feature
can automatically change control
parameter values for operation over a
large temperature range. Ten diff erent
temperature zones can be loaded into
the instrument, which will select the next
appropriate value on setpoint change.
www.lakeshore.com Lake Shore Cryotronics, Inc. (614) 891-2244 fax: (614) 818-1600 e-mail: info@lakeshore.com
Interface
The Model 325 includes both parallel
(IEEE-488) and serial (RS-232C) computer
interfaces. In addition to data gathering,
nearly every function of the instrument
can be controlled via computer interface.
Sensor curves can also be entered and
manipulated through either interface
using the Lake Shore curve handler
software program.
Confi gurable Display
The Model 325 off ers a bright, easy to
read LCD display that simultaneously
displays up to four readings. Display data
includes input and source annunciators
for each reading. All four display locations
can be confi gured by the user. Data
from either input can be assigned to
any of the four locations, and the user's
choice of temperature or sensor units
can be displayed. Heater range and
control output as current or power can
be continuously displayed for immediate
feedback on control operation. The
channel A or B indicator is underlined
to indicate which channel is being
controlled by the displayed control loop.
Model 325 Rear Panel Connections
Loop 1 Heater Output
Serial (RS-232C) I/O (DTE)
Line Input Assembly
Normal (Default) Display Confi guration
The display provides four reading locations.
Readings from each input and the control
setpoint can be expressed in any combination
of temperature or sensor units, with heater
output expressed as a percent of full scale
current or power.
Flexible Confi guration
Reading locations can be confi gured by the user
to meet application needs. The character preceding
the reading indicates input A or B or setpoint S.
The character following the reading indicates
measurement units.
Curve Entry
The Model 325 display off ers the fl exibility to
support curve, SoftCal™, and zone entry. Curve
entry may be performed accurately and to full
resolution via the display and keypad as well as
computer interface.
Loop 2 Heater Output
Sensor Input Connectors
IEEE-488 Interface
3
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