The Model 331 has been replaced by the Model 335


Input Specifications
Diodenegative0 V to 2.5 V
10 µA
±0.05%12, 13
100 µV10 µV±80 µV ±0.005% of rdg ±20 µV
negative0 V to 7.5 V
10 µA
±0.05%12, 13
100 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
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 331 user manual for details
14 Current source error is removed during calibration
15 Accuracy specification does not include errors from room temperature compensation
Number of inputs
Input configuration

Each input is factory configured as either diode/RTD or thermocouples

Sensor inputs optically isolated from other circuits but not from each other
A/D resolution
Input accuracy
Sensor dependent – refer to Input Specifications table
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

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

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
Diodes: Silicon, GaAlAs
RTDs: 100 Ω Platinum, 1000 Ω Platinum, Germanium, Carbon-Glass, Cernox™, and Rox™
Most thermocouple types
DT-470, DT-500D. DT-670, PT-100, PT-1000,
RX-102A, RX-202A
Type E, Type K, Type T, AuFe 0.07% vs. Cr,
AuFe 0.03% vs Cr,
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
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 source
Variable 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

2 line by 20 character, 9 mm character height, vacuum fluorescent display
Number of reading
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
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
Display annunciators
Control input, remote, alarm, tuning, ramp, max, min, linear
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 factory 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
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
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
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 temperature

15 °C to 35 °C at rated accuracy, 10 ºC to 40 ºC at reduced accuracy
Power requirement
100, 120, 220, 240 VAC, (+6%, -10%), 50 or 60 Hz, 120 VA

216 mm W × 89 mm H × 368 mm D
(8.5 in × 3.5 in × 14.5 in), half rack
4.8 kg (10.5 lb)
Approval CE mark

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