Model 325 Cryogenic Temperature Controller

Input Specifications

	Sensor Temperature Coefficient	Input Range	Excitation Current	Display Resolution	Measurement Resolution	Electronic Accuracy	Electronic Control 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
Diode	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 W to 500 W	1 mA¹⁴	10 mW	2 mW	±0.004 W ±0.01% of rdg	±4 mW
PTC RTD	positive	0 W to 5000 W	1 mA¹⁴	100 mW	20 mW	±0.04 W ±0.02% of rdg	±40 mW
NTC RTD	negative	0 W to 7500 W	10 µA ±0.05%¹⁴	100 mW	40 mW	±0.1 W ±0.04% of rdg	±80 mW
Thermocouple	positive	±25 mV	NA	1 µV	0.4 µV	±1 µV ±0.05% of rdg¹⁵	0.8 µV
Thermocouple	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 ideal thermal system ¹² Control 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 detaiils				¹⁴ Current source error is removed during caliibration ¹⁵ Accuracy specification does not include errors from room temperature compensation

Thermometry
Number of inputs	2
Input configuration	Each input is factory configured as either diode/RTD or thermocouple
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 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

Sensor Input Configuration

	Diode/RTD	Thermocouple
Measurement type	4-lead differential	2-lead, room temperature compensated
Excitation	Constant current with current reversal for RTDs	NA
Supported sensors	Diodes: Silicon, GaAlAs RTDs: 100 W Platinum, 1000 W 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 connector	6-pin DIN	Ceramic isothermal block

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 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 W Setting	50 W 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 W to 25 W	40 W to 50 W
Heater load for max power	25W	50 W
Ranges	2 (2.5W/25 W)
Heater noise (<1 kHz)	1 µV + 0.01% of output
Grounding	Output referenced to chassis ground
Heater connector	Dual banana

Loop 2 Heater Output

	25 W Setting	50 W 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 W	≥ 50 W
Heater load for max power	25W	50 W
Ranges	1
Heater noise (<1 kHz)	50 µV + 0.01% of output
Grounding	Output referenced to chassis ground
Heater connector	Detachable terminal block

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Front Panel
Display	2- 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 W
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 display	Numerical 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

Interfaces
IEEE-488.2 interface
Features	SH1, AH1, T5, L4, SR1, RL1, PP0, DC1, DT0, C0, E1
Reading rate	To 10 rdg/s on each point
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 rdgs/s on each input

General
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
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

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