325 temperature controller specifications

Input specifications

 Sensor temperature coefficient Input range Excitation current Display resolution Measurement resolution Electronic accuracy11Electronic control stability12
Diodenegative0 V to 2.5 V 10 µA ±0.05%13, 14 100 µV10 µV±80 µV ±0.005% of rdg ±20 µV
negative0 V to 7.5 V10 µA ±0.05%13, 14100 µV20 µV±320 µV ±0.01% of rdg±40 µV
PTC RTD positive0 Ω to 500 Ω1 mA15 10 mΩ2 mΩ±0.004 Ω ±0.01% of rdg±4 mΩ
positive0 Ω to 5000 Ω1 mA15100 mΩ20 mΩ±0.04 Ω ±0.02% of rdg±40 mΩ
NTC RTD negative0 Ω to 7500 Ω10 µA ±0.05%15100 mΩ40 mΩ±0.1 Ω ±0.04% of rdg±80 mΩ
Thermocouple positive±25 mVNA1 µV0.4 µV±1 µV ±0.05% of rdg160.8 µV
positive±50 mVNA1 µV0.4 µV±1 µV ±0.05% of rdg160.8 µV

11 With current reversal enabled for RTD measurements
12 Control stability of the electronics only, in ideal thermal system
13 Control source error has negligible effect on measurement accuracy
14 Diode input excitation current can be set to 1 mA — refer to the Model 325 user manual for details
15 Current source error is removed during calibration
16 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 thermocouple


Sensor inputs optically isolated from other circuits but not from each other

A/D resolution


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


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


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 sensorsDiodes: 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-202A Type E, Type K, Type T, AuFe 0.07% vs. Cr, AuFe 0.03% vs Cr
Input connector6-pin DIN Ceramic isothermal block


Control loops


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 – see Input Specification table

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

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 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 µV + 0.01% of output
GroundingOutput referenced to chassis ground  
Heater connector Dual banana

Loop 2 heater output

 25 Ω setting 50 Ω setting
Type Variable DC voltage source
D/A resolution 16-bit
Max power 1 W2 W
Max voltage 5 V 10 V
Current compliance 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
GroundingOutput referenced to chassis ground
Heater connector Detachable terminal block

Front panel

Display2- line × 20-character, liquid crystal display with 5.5 mm character height

No. of reading displays

1 to 4

Display units

K, ºC, V, mV and Ω

Reading source

Temperature, sensor units

Display update rate

2 rdg/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 displayNumerical display in percent of full scale for power or current

Heater output resolution


Display annunciators

Control input, Remote, Autotune


20-key membrane, numeric and specific functions

Front panel features

Front panel curve entry, keypad lock-out


IEEE-488.2 interface



SH1, AH1, T5, L4, SR1, RL1, PP0, DC1, DT0, C0, E1

Reading rate

To 10 rdg/s on each point

Software support

LabVIEW™ driver

Serial interface 


Electrical format

Baud rates

9600, 19200, 38400, 57600


9-pin D-style, DTE configuration

Reading rate

To 10 rdgs/s on each input


Ambient temperature


15 °C to 35 °C at rated accuracy, 5 ºC to 40 ºC at reduced accuracy


Power requirement

100, 120, 220, 240 VAC, +6%, -10%, 50 or 60 Hz, 85 VA


216 mm W × 89 mm H × 368 mm D (8.5 in × 3.5 in × 14.5 in), half rack


4.00 kg (8.82 lb)


CE mark

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