Lake Shore 325 User manual

Model 325
Temperature Controller
www.lakeshore.com

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Model 325
Temperature Controller
 Operates down to 1.2 K with
appropriate sensor
 Two sensor inputs
 Supports diode, RTD, and
thermocouple sensors
 Sensor excitation current
reversal eliminates thermal
EMF errors in resistance sensors
 Two autotuning control loops:
25 W and 2 W maximum
 Control loop 2: variable DC
voltage source from 0 to 10 V
maximum
 IEEE-488 and RS-232C
interfaces
1 The Lake Shore SoftCal™ algorithm for silicon diode
and platinum RTD sensors is a good solution for
applications requiring more accuracy than a standard
sensor curve but not in need of traditional calibration.
SoftCal uses the predictability of a standard curve to
improve the accuracy of an individual sensor around a
few known temperature reference points.
Introduction
The Model 325 dual-channel temperature
controller is capable of supporting
nearly any diode, RTD, or thermocouple
temperature sensor. Two independent
PID control loops with heater outputs
of 25 W and 2 W are configured to drive
either a 50 Ω or 25 Ω load for optimal
cryocooler control flexibility. Designed
with ease of use, functionality, and
value in mind, the Model 325 is ideal
for general-purpose laboratory and
industrial temperature measurement and
control applications.
Sensor Inputs
The Model 325 temperature controller
features two inputs with a high-
resolution 24-bit analog-to-digital
converter and separate current sources
for each input. Constant current
excitation allows temperature to be
measured and controlled down to
2.0 K using appropriate Cernox™ RTDs
or down to 1.4 K using silicon diodes.
Thermocouples allow for temperature
measurement and control above 1,500 K.
Sensors are optically isolated from other
instrument functions for quiet and
repeatable sensor measurements. The
Model 325 also uses current reversal to
eliminate thermal EMF errors in resistance
sensors. Sensor data from each input is
updated up to ten times per second, with
display outputs twice each second.
Standard temperature response curves
for silicon diodes, platinum RTDs,
ruthenium oxide RTDs, and many
thermocouples are included. Up to fifteen
200-point CalCurves® (for Lake Shore
calibrated temperature sensors) or user
curves can be stored into non-volatile
memory. A built-in SoftCal®1 algorithm
can be used to generate curves for silicon
diodes and platinum RTDs for storage as
user curves. The Lake Shore curve handler
software program allows sensor curves to
be easily loaded and manipulated.
Sensor inputs for the Model 325 are
factory configured and compatible with
either diodes/RTDs or thermocouple
sensors. Your choice of two diode/
RTD inputs, one diode/RTD input
and one thermocouple input, or two
thermocouple inputs must be specified at
time of order and cannot be reconfigured
in the field. Software selects appropriate
excitation current and signal gain levels
when the sensor type is entered via the
instrument front panel.

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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.
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.
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 1 Heater Output
 Serial (RS-232C) I/O (DTE)
 Line Input Assembly
Model 325 Rear Panel Connections
 Loop 2 Heater Output
 Sensor Input Connectors
 IEEE-488 Interface
  

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Sensor Selection
Silicon diodes are the best choice for general
cryogenic use from 1.4 K to above room temperature.
Diodes are economical to use because they follow
a standard curve and are interchangeable in many
applications. They are not suitable for use in ionizing
radiation or magnetic fields.
Cernox™ thin-film RTDs offer high sensitivity and
low magnetic field-induced errors over the 2 K to
420 K temperature range. Cernox sensors require
calibration.
Platinum RTDs offer high uniform sensitivity from
30 K to over 800 K. With excellent reproducibility,
they are useful as thermometry standards. They
follow a standard curve above 70 K and are
interchangeable in many applications.
Sensor Temperature Range (sensors sold separately)
Model Useful Range Magnetic Field Use
Diodes Silicon Diode DT-670-SD 1.4 K to 500 K T ≥ 60 K & B ≤ 3 T
Silicon Diode DT-670E-BR 30 K to 500 K T ≥ 60 K & B ≤ 3 T
Silicon Diode DT-414 1.4 K to 375 K T ≥ 60 K & B ≤ 3 T
Silicon Diode DT-421 1.4 K to 325 K T ≥ 60 K & B ≤ 3 T
Silicon Diode DT-470-SD 1.4 K to 500 K T ≥ 60 K & B ≤ 3 T
Silicon Diode DT-471-SD 10 K to 500 K T ≥ 60 K & B ≤ 3 T
GaAlAs Diode TG-120-P 1.4 K to 325 K T > 4.2 K & B ≤ 5 T
GaAlAs Diode TG-120-PL 1.4 K to 325 K T > 4.2 K & B ≤ 5 T
GaAlAs Diode TG-120-SD 1.4 K to 500 K T > 4.2 K & B ≤ 5 T
Positive Temperature 100 Ω Platinum PT-102/3 14 K to 873 K T > 40 K & B ≤ 2.5 T
Coefficient RTDs 100 Ω Platinum PT-111 14 K to 673 K T > 40 K & B ≤ 2.5 T
Rhodium-Iron RF-800-4 1.4 K to 500 K T > 77 K & B ≤ 8 T
Rhodium-Iron RF-100T/U 1.4 K to 325 K T > 77 K & B ≤ 8 T
Negative Cernox™ CX-1010 2 K to 325 K5 T > 2 K & B ≤ 19 T
Temperature Cernox™ CX-1030-HT 3.5 K to 420 K3, 6 T > 2 K & B ≤ 19 T
Coefficient RTDs2 Cernox™ CX-1050-HT 4 K to 420 K3, 6 T > 2 K & B ≤ 19 T
Cernox™ CX-1070-HT 15 K to 420 K3 T > 2 K & B ≤ 19 T
Cernox™ CX-1080-HT 50 K to 420 K3 T > 2 K & B ≤ 19 T
Germanium GR-200A/B-1000 2.2 K to 100 K4 Not Recommended
Germanium GR-200A/B-1500 2.6 K to 100 K4 Not Recommended
Germanium GR-200A/B-2500 3.1 K to 100 K4 Not Recommended
Carbon-Glass CGR-1-500 4 K to 325 K5 T > 2 K & B ≤ 19 T
Carbon-Glass CGR-1-1000 5 K to 325 K5 T > 2 K & B ≤ 19 T
Carbon-Glass CGR-1-2000 6 K to 325 K5 T > 2 K & B ≤ 19 T
Rox™ RX-102A 1.4 K to 40 K5 T > 2 K & B ≤ 10 T
Thermocouples Type K 9006-006 3.2 K to 1505 K Not Recommended
Type E 9006-004 3.2 K to 934 K Not Recommended
Chromel-
AuFe 0.07% 9006-002 1.2 K to 610 K Not Recommended
2
Single excitation current may limit the low temperature range of NTC resistors
3 Non-HT version maximum temperature: 325 K
4 Low temperature limited by input resistance range
5 Low temperature specified with self-heating error: ≤5 mK
6 Low temperature specified with self-heating error: ≤12 mK

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Typical Sensor Performance – see Appendix F for sample calculations of typical sensor performance
Example Temp Nominal Typical Measurement Electronic Temperature Electronic Control
Lake Shore Resistance/ Sensor Resolution: Accuracy: Accuracy including Stability8:
Sensor Voltage Sensitivity7 Temperature Temperature Electronic Accuracy, Temperature
Equivalents Equivalents CalCurve™, and Equivalents
Calibrated Sensor
Silicon Diode DT-670-SD-13 1.4 K 1.644 V -12.49 mV/K 0.8 mK ±13 mK ±25 mK ±1.6 mK
with 1.4H 77 K 1.028 V -1.73 mV/K 5.8 mK ±76 mK ±98 mK ±11.6 mK
calibration 300 K 0.5597 V -2.3 mV/K 4.4 mK ±47 mK ±79 mK ±8.8 mK
500 K 0.0907 V -2.12 mV/K 4.8 mK ±40 mK ±90 mK ±9.6 mK
Silicon Diode DT-470-SD-13 1.4 K 1.6981 V -13.1 mV/K 0.8 mK ±13 mK ±25 mK ±1.6 mK
with 1.4H 77 K 1.0203 V -1.92 mV/K 5.2 mK ±69 mK ±91 mK ±10.4 mK
calibration 300 K 0.5189 V -2.4 mV/K 4.2 mK ±45 mK ±77 mK ±8.4 mK
475 K 0.0906 V -2.22 mV/K 4.6 mK ±39 mK ±89 mK ±9.2 mK
GaAlAs Diode TG-120-SD 1.4 K 5.391 V -97.5 mV/K 0.2 mK ±7 mK ±19 mK ±0.4 mK
with 1.4H 77 K 1.422 V -1.24 mV/K 16.2 mK ±180 mK ±202 mK ±32.4 mK
calibration 300 K 0.8978 V -2.85 mV/K 7 mK ±60 mK ±92 mK ±14 mK
475 K 0.3778 V -3.15 mV/K 6.4 mK ±38 mK ±88 mK ±12.8 mK
100 Ω Platinum RTD PT-103 30 K 3.660 Ω 0.191 Ω/K 10.5 mK ±23 mK ±33 mK ±21 mK
500 Ω Full Scale with 1.4J 77 K 20.38 Ω 0.423 Ω/K 4.8 mK ±15 mK ±27 mK ±9.6 mK
calibration 300 K 110.35 Ω 0.387 Ω/K 5.2 mK ±39 mK ±62 mK ±10.4 mK
500 K 185.668 Ω 0.378 Ω/K 5.3 mK ±60 mK ±106 mK ±10.6 mK
Cernox™ CX-1050-SD-HT9 4.2 K 3507.2 Ω -1120.8 Ω/K 36 µK ±1.4 mK ±6.4 mK ±72 µK
with 4M 77 K 205.67 Ω -2.4116 Ω/K 16.6 mK ±76 mK ±92 mK ±33.2 mK
calibration 300 K 59.467 Ω -0.1727 Ω/K 232 mK ±717 mK ±757 mK ±464 mK
420 K 45.030 Ω -0.0829 Ω/K 483 mK ±1.42 K ±1.49 K ±966 mK
Germanium GR-200A-1000 2 K 6674 Ω -9930 Ω/K 4 µK ±0.3 mK ±4.3 mK ±8 µK
with 1.4D 4.2 K 1054 Ω -526 Ω/K 76 µK ±1 mK ±5 mK ±152 µK
calibration 10 K 170.9 Ω -38.4 Ω/K 1 mK ±4.4 mK ±9.4 mK ±2 mK
100 K 2.257 Ω -0.018 Ω/K 2.22 K ±5.61 K ±5.626 K ±4.44 K
Carbon-Glass CGR-1-2000 4.2 K 2260 Ω -2060 Ω/K 20 µK ±0.5 mK ±4.5 mK ±40 µK
with 4L 77 K 21.65 Ω -0.157 Ω/K 255 mK ±692 mK ±717 mK ±510 mK
calibration 300 K 11.99 Ω -0.015 Ω/K 2.667 K ±7 K ±7.1 K ±5.334 K
Thermocouple Type K 75 K -5862.9 µV 15.6 µV/K 26 mK ±0.25 K10
Calibration not available ±52 mK
50 mV 300 K 1075.3 µV 40.6 µV/K 10 mK ±0.038 K10
from Lake Shore ±20 mK
600 K 13325 µV 41.7 µV/K 10 mK ±0.184 K10 ±20 mK
1505 K 49998.3 µV 36.006 µV/K 12 mK ±0.73 K10 ±24 mK
7 Typical sensor sensitivities were taken from representative calibrations for the sensor listed
8 Control stability of the electronics only, in an ideal thermal system
9 Non-HT version maximum temperature: 325 K
10 Accuracy specification does not include errors from room temperature compensation

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Thermometry
Number of inputs 2
Input configuration Each input is factory configured for either diode/RTD
or thermocouple
Isolation Sensor inputs optically isolated from other circuits
but not each other
A/D resolution 24-bit
Input accuracy Sensor dependent – refer to Input Specifications table
Measurement resolution Sensor dependent – refer to Input Specifications table
Maximum update rate 10 rdg/s on each input (except 5 rdg/s on input A when
configured as thermocouple)
User curves Room for 15 200-point CalCurves™ or user curves
SoftCal™ Improves accuracy of DT-470 diode to ±0.25 K
from 30 K to 375 K; improves accuracy of platinum RTDs to
±0.25 K from 70 K to 325 K; stored as user curves
Filter Averages 2 to 64 input readings
Control
Control loops 2
Control type Closed loop digital PID with manual heater output or open loop
Tuning Autotune (one loop at a time), PID, PID zones
Control stability Sensor dependent – see Input Specification table
PID control settings
Proportional (gain) 0 to 1000 with 0.1 setting resolution
Integral (reset) 1 to 1000 (1000/s) with 0.1 setting resolution
Derivative (rate) 1 to 200% with 1% resolution
Manual output 0 to 100% with 0.01% setting resolution
Zone control 10 temperature zones with P, I, D, manual heater out,
and heater range
Setpoint ramping 0.1 K/min to 100 K/min
Safety limits Curve temperature, power up heater off, short circuit protection
Sensor Input Configuration
Model 325 Specifications
Input Specifications
14 Current source error is removed during calibration
15 Accuracy specification does not include errors from
room temperature compensation
Diode/RTD Thermocouple
Measurement type 4-lead differential 2-lead, room temperature
compensated
Excitation Constant current with NA
current reversal for RTDs
Supported sensors Diodes: Silicon, GaAlAs Most thermocouple types
RTDs: 100 Ω Platinum,
1000 Ω Platinum, Germanium,
Carbon-Glass, Cernox™,
and Rox™
Standard curves DT-470, DT-500D, DT-670, Type E, Type K, Type T,
PT-100, PT-1000, AuFe 0.07% vs. Cr,
RX-102A, RX-202A AuFe 0.03% vs. Cr
Input connector 6-pin DIN Ceramic isothermal block
Sensor Input Excitation Display Measurement Electronic Electronic
Temperature Range Current Resolution Resolution Accuracy Control
Coefficient Stability11
Diode negative 0 V to 2.5 V 10 µA ±0.05%12, 13 100 µV 10 µV ±80 µV ±0.005% of rdg ±20 µV
negative 0 V to 7.5 V 10 µA ±0.05%12, 13 100 µV 20 µV ±80 µV ±0.01% of rdg ±40 µV
PTC RTD positive 0 Ω to 500 Ω 1 mA14 10 mΩ 2 mΩ ±0.004 Ω ±0.01% of rdg ±4 mΩ
positive 0 Ω to 5000 Ω 1 mA14 100 mΩ 20 mΩ ±0.04 Ω ±0.02% of rdg ±40 mΩ
NTC RTD negative 0 Ω to 7500 Ω 10 µA ±0.05%14 100 mΩ 40 mΩ ±0.1 Ω ±0.04% of rdg ±80 mΩ
Thermocouple positive ±25 mV NA 1 µV 0.4 µV ±1 µV ±0.05% of rdg15 ±0.8 µV
positive ±50 mV NA 1 µV 0.4 µV ±1 µV ±0.05% of rdg15 ±0.8 µV
11 Control stability of the electronics only, in an ideal thermal system
12 Current source error has negligible effect on measurement accuracy
13 Diode input excitation current can be set to 1 mA – refer to the Model 325 user manual for details

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Part number Description
325 Two diode/RTD inputs
325-T1 One diode/RTD, one thermocouple input
325-T2 Two thermocouple inputs
Specify line power option*
VAC-100 Instrument configured for 100 VAC with U.S. power cord
VAC-120 Instrument configured for 120 VAC with U.S. power cord
VAC-120-ALL Instrument configured for 120 VAC with U.S. power cord
and universal Euro line cord and fuses for 220/240 VAC setting
VAC-220 Instrument configured for 220 VAC with universal
Euro line cord
VAC-240 Instrument configured for 240 VAC with universal
Euro line cord
*Other country line cords available, consult Lake Shore
Accessories included
106-009 Heater output connector (dual banana jack)
106-233 Sensor input mating connector (6-pin DIN plugs)
106-735 Terminal block, 2-pin
—— Calibration certificate
MAN-325 Model 325 user manual
Accessories available
6201 1 m (3.3 ft long) IEEE-488 (GPIB) computer interface
cable assembly
8001-325 CalCurve™, factory installed – the breakpoint
table from a calibrated sensor stored in the instrument
(extra charge for additional sensor curves)
CAL-325-CERT Instrument recalibration with certificate
CAL-325-DATA Instrument recalibration with certificate and data
RM-½ Kit for mounting one ½ rack temperature controller in a
482.6 mm (19 in) rack, 90 mm (3.5 in) high
RM-2 Kit for mounting two ½ rack temperature controllers in a
482.6 mm (19 in) rack, 135 mm (5.25 in) high
All specifications are subject to change without notice
Ordering Information
Front Panel
Display 2-line × 20-character, liquid crystal display with 5.5 mm
character height
Number of reading displays 1 to 4
Display units K, °C, V, mV, Ω
Reading source Temperature, sensor units
Display update rate 2 rdg/s
Temp display resolution 0.001° from 0° to 99.999°, 0.01° from 100° to 999.99°,
0.1° above 1000°
Sensor units
display resolution Sensor dependent; to 5 digits
Other displays Setpoint, Heater Range, and Heater Output (user selected)
Setpoint setting resolution Same as display resolution (actual resolution is sensor dependent)
Heater output display Numeric display in percent of full scale for power or current
Heater output resolution 1%
Display annunciators Control Input, Remote, Autotune
Keypad 20-key membrane, numeric and specific functions
Front panel features Front panel curve entry, keypad lock-out
Interface
IEEE-488 interface
Features SH1, AH1, T5, L4, SR1, RL1, PP0, DC1, DT0, C0, E1
Reading rate To 10 rdg/s on each input
Software support LabVIEW™ driver (consult factory for availability)
Serial interface
Electrical format RS-232C
Baud rates 9600, 19200, 38400, 57600
Connector 9-pin D-style, DTE configuration
Reading rate To 10 rdg/s on each input
General
Ambient temperature 15 °C to 35 °C at rated accuracy, 5 °C to 40 °C at reduced accuracy
Power requirement 100, 120, 220, 240 VAC, +6%, -10%, 50 or 60 Hz, 85 VA
Size 216 mm W × 89 mm H × 368 mm D
(8.5 in × 3.5 in × 14.5 in), half rack
Weight 4.00 kg (8.82 lb)
Approval CE mark
Loop 2 Heater Output
25 Ω Setting 50 Ω Setting
Type Variable DC voltage source
D/A resolution 16-bit
Max power 1 W 2 W
Max voltage 5 V 10 V
Current compliance (min) 0.2 A
Heater load range ≥ 25 Ω ≥ 50 Ω
Heater load for max power 25 Ω50 Ω
Ranges 1
Heater noise (<1 kHz) 50 µV + 0.01% of output
Grounding Output referenced to chassis ground
Heater connector Detachable terminal block
Loop 1 Heater Output
25 Ω Setting 50 Ω Setting
Type Variable DC current source
D/A resolution 16-bit
Max power 25 W
Max current 1 A 0.71 A
Voltage compliance (min) 25 V 35.4 V
Heater load range 20 Ω to 25 Ω40 Ω to 50 Ω
Heater load for max power 25 Ω50 Ω
Ranges 2 (2.5 W/25 W)
Heater noise (<1 kHz) 1 µA + 0.01% of output
Grounding Output referenced to chassis ground
Heater connector Dual banana

Lake Shore Cryotronics, Inc.
575 McCorkle Boulevard
Westerville, OH 43082-8888 USA
Tel [phone]
Fax [phone]
e-mail [e-mail]
www.lakeshore.com
Established in 1968, Lake Shore Cryotronics, Inc.
is an international leader in developing innovative
measurement and control solutions. Founded by
Dr. John M. Swartz, a former professor of electrical
engineering at the Ohio State University, and his
brother David, Lake Shore produces equipment
for the measurement of cryogenic temperatures,
magnetic fields, and the characterization of
the physical properties of materials in
temperature and magnetic environments.