The Model 331 is discontinued. Please consider the Model 335.

Model 331 Specifications

 Sensor temperature coefficient Input range Excitation current Display resolution Measurement resolution Electronic accuracy Electronic control stability10
Diodenegative0 V to 2.5 V 10 µA ±0.05%12, 13100 µV10 µV±80 µV ±0.005% of rdg ±20 µV
negative0 V to 7.5 V10 µA ±0.05%12, 13100 µV20 µV±80 µV ±0.01% of rdg±40 µV
PTC RTD positive0 Ω to 500 Ω1 mA14 10 mΩ2 mΩ±0.004Ω ±0.01% of rdg±4 mΩ
positive0 Ω to 5000 Ω1 mA14100 mΩ20 mΩ±0.04Ω ±0.02% of rdg±40 mΩ
NTC RTD negative0 Ω to 7500 Ω10 µA ±0.05%14100 mΩ40 mΩ±0.1 Ω ±0.04% of rdg±80 mΩ
Thermocouple positive±25 mVNA1 µV0.4 µV±1 µV ±0.05% of rdg150.8 µV
positive±50 mVNA1 µV0.4 µV±1 µV ±0.05% of rdg150.8 µV

11 Control stability of the electronics only, in an ideal thermal system
Current source error has negligible effect on measurement accuracy
13 Diode input excitation current can be set to 1 mA — refer to the Model 331 user manual for details
Current source error is removed during calibration
15 Accuracy specification does not include errors from room temperature compensation


Number of inputs 2
Input configuration Each input is factory configured as either diode/RTD or thermocouples
Isolation Sensor inputs optically isolated from other circuits but not from 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 readings/s on each input (except 5 readings/s on input A when configured as thermocouple)
User curves Room for twenty 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
Math Maximum, minimum, and linear equation (Mx + B) or M(x + B)
Filter Averages 2 to 64 input readings

Sensor input configuration

Measurement type 4-lead differential 2-lead, room temperature compensated
ExcitationConstant current with current reversal for RTDs NA
Supported sensors Diodes: Silicon, GaAlAs RTDs: 100 Ω Platinum, 1000 Ω Platinum, Germanium, Carbon-Glass, Cernox®, and Rox™Most thermocouple types
Standard curves DT-470, DT-500D. DT-670, PT-100, PT-1000, RX-102A, RX-202AType E, Type K, Type T, AuFe 0.07% vs. Cr, AuFe 0.03% vs Cr
Input connector 6-pin DIN Ceramic isothermal block


Control loops Two on 331S, one on 331E
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 — to 2× measurement resolution (in an ideal thermal system)
PID control parameters
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

Heater output

 Loop 1 Loop 2
Heater output type Variable DC current sourceVariable DC voltage source
Heater output D/A resolution 18-bit16-bit
Max heater power 50 W 1 W
Max heater output current 1 A 0.1 A
Heater output complaince 50 V 10 V
Heater output ranges 3 decade steps in power 1
Heater load type ResistiveResistive
Heater load range 10 Ω to 100 Ω recommended 100 Ω minimum
Heater load for max power 50 Ω100 Ω
Heater noise (<1 kHz) RMS 50 µV + 0.01% of output voltage <0.3 mV
IsolationOptical isolation between output and other circuits None
Heater connector Dual banana Detachable terminal block

Loop 1 full scale heater power at typical resistance

Heater resistance Heater rangeHeater power
10 Ω Low100 mW
Med1 W
High10 W
25 Ω Low250 mW
Med2.5 W
High25 W
50 Ω Low500 mW
Med5 W
High50 W

Front panel

Display 2 line by 20 character, 9 mm character height, vacuum fluorescent display
Number of reading displays 1 to 4
Display units K, ºC, V, mV and Ω
Reading source Temperature, sensor units, max, min, and linear equation
Display update rate All readings twice per s
Temp display resolution 0.001º from 0º to 99.999º, 0.01º from 100º to 999.99º, 0.1º above 1000º
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 in sensor dependent)
Heater output display Numerical display in percent of full scale for power or current
Heater output resolution 1%
Display annunciators Control input, remote, alarm, tuning, ramp, max, min, linear
Keypad 20 full-travel keys, numeric and specific functions
Front panel features Front panel curve entry, display brightness control, and keypad lock-out


IEEE-488.2 interface (331S)

FeaturesSH1, AH1, T5, L4, SR1, RL1, PP0, DC1, DT0, C0, E1
Reading rate To 10 readings per s on each point
Software Support LabVIEW™ driver (consult Lake Shore for availability)

Serial interface

Electrical format RS-232C
Max baud rate 9600 baud
Connector9-pin D-sub
Reading rate To 10 readings/s on each input (at 9600 baud)
Special interface features Model 330 command emulation mode


Number 4, high and low for each input
Data source Temperature, sensor units, linear equation
SettingsSource, high setpoint, low setpoint,deadband, latching or non-latching, and audible on/off
Actuators Display, annunciator, beeper, and relays

Relays (331S)

Number 2
Contacts Normally open (NO), normally closed (NC), and (C) common
Contact Rating 30 VDC at 5 A
Operation Activate relays on high, low or both alarms for either input or manual
Connector Detachable terminal block

Analog voltage output (331S)

Scale User selected
Update rate 10 readings per s
Data source Temperature, sensor units, linear equation
Settings Input, source, top of scale, bottom of scale, or manual
Range ±10 V
Resolution 0.3 mV
Accuracy±2.5 mV
Min load resistance 100 Ω (short-circuit protected)


Ambient temperature15 °C to 35 °C at rated accuracy, 10 ºC to 40 ºC at reduced accuracy
Power requirement100, 120, 220, 240 VAC, (+6%, -10%), 50 or 60 Hz, 120 VA
Size216 mm W × 89 mm H × 368 mm D (8.5 in × 3.5 in × 14.5 in), half rack
Weight4.8 kg (10.5 lb)
ApprovalCE mark

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