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Model 24C Cryogenic Temperature Controller

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Front Panel
Rear Panel

M24Cfront

Highlights of the Model 24C:

Four multipurpose input channels support Diode, Platinum RTD and most cryogenic NTC resistive temperature sensors. Two thermocouple inputs are optional.
Operation from 275mK to over 1500K with an appropriate sensor. Constant-Voltage, AC excitation of resistive sensors minimizes errors and extends their useful temperature range.
Dual loop control. Loop #1: 50-Watt, threerange. Loop #2: 10-Watt.
Large, bright and highly configurable display.
Synchronous input filter improves control accuracy and stability in cryocooler based systems.

Two dry-contact relay outputs.
Data logging to internal Non-Volatile memory.
Fail-safe cryostat protection features protect user equipment from damage.
Table mode control automatically switches the loop input sensor to allow smooth, continuous control over a wide range of temperature.
Remote interfaces include 100/10 Ethernet and RS-232. IEEE-488.2 (GPIB) and USB are optional.
Remote command language is IEEE SCPI compliant.
National Instruments, Inc. LabVIEW™ drivers are available for all interfaces.

M44rear

Input Connectors: DIN-6 receptacles provide 4-wire measurement connection plus shield.
Loop #1: 50-Watt heater output. Dual Banana Plug with chassis ground lug.
Loop #2: 10-Watt heater, part of a 10 pin detachable terminal block.
Loop #3 and #4: 10-Volt output. Detachable terminal block.
Relay Outputs (2): Detachable terminal block.
Ethernet: RJ-45 with LAN activity indicator LEDs.
IEEE-488: Option connects to Ethernet port.
RS-232: Null-modem connector (DB-9, pins).
USB: Option connects to RS-232 port.
AC Power: RFI filtered Power Entry Module including fuse drawer and line voltage selector.

General Description

The Model 24C is a four-input, four control loop cryogenic temperature controller designed for general purpose laboratory and industrial use. Each input is independent and capable of temperature measurement to <300mK with an appropriate temperature sensor.

The Four-output control loop circuits feature a primary 50W heater, a secondary heater of 10W and two 10-Volt non-powered outputs. All control modes are supported by all outputs.

The 24C front panel incorporates a high resolution graphics type TFT-LCD with an exceptionally wide viewing angle. Complete instrument status can be seen at a glance, even from across the room.

The 24C front panel incorporates a high resolution graphics TFT type Liquid Crystal Display with an exceptionally wide viewing angle. With it's bright white LED backlight, complete instrument status can be seen at a glance, even from across the room.

Flexible Inputs: The Model 24C has four identical input channels, each of which can be easily configured to operate virtually any type of cryogenic thermometer.

A unique feature of the Model 24C is the use of a ratiometric AC resistance bridge to measure all types of temperature sensors. Excitation is a voltage-source followed by passive attenuators for minimum Johnson noise. Sensor voltage and excitation current are separately measured using dual amplifiers and dual analog-to-digital converters.

The resistance bridge is used in a constant-voltage AC mode to provide robust support for the Negative Temperature Coefficient (NTC) sensors. These include
Ruthenium-oxide, Carbon-Glass, Cernox™, Carbon-Ceramic, Germanium and several others. Since they have a negative temperature coefficient, the use of a constant-voltage measurement will reduce, rather than increase, power dissipation in the sensor as temperature decreases. By maintaining the lowest possible power level, sensor self-heating is minimized and useful temperature range is greatly increased.

The excitation source in the Model 24C is continuously variable so there are no steps in sensor self-heating. AC excitation used with resistor sensors is a 1.67Hz bipolar square wave. This effectively eliminates DC offset errors including the thermal EMF induced offsets that often occur in some cryogenic systems.

Positive Temperature Coefficient (PTC) resistor sensors including Platinum and Rhodium-Iron RTDs use the resistance bridge in its passive, AC mode. Here, excitation current gradually increases as temperature decreases.

Platinum RTD sensors use a built-in DIN standard calibration curve that has been extended to 14K for cryogenic use.

Diode sensors are supported over their full temperature range by using the Model 24C's bridge in a DC, constant-current mode. This mode servos the excitation source to the sensor current to provide the constant-current required by these sensors.

Four Control Loops: The Loop #1 heater output is a linear, low noise RFI filtered current source that can provide up to 1.0 Ampere into 50-Ohm or 25-Ohm resistive loads. Three full-scale ranges are available in decade increments down to 500mW.

Loop #2 is a linear heater with that will provide 10-Watts into a 50-Ohm load.

Loop #3 and #4 are non-powered voltage outputs intended to control an external booster power supply. Output is zero to 10-Volts.

All control loops are completely independent and any loop may be controlled by any sensor input.

Relays: There are two dry-contact mechanical relays. Each may be independently programmed to assert or clear based on a high or low temperature condition or a detected sensor fault.

Remote Control: Standard remote interfaces include 100/10 Ethernet and RS-232. IEEE-488(GPIB) and USB are optional.

In order to eliminate ground-loop and noise pickup problems commonly associated with IEEE-488 systems, the internal IEEE-488 circuitry was moved to an external module that interfaces to the directly to the instrument's isolated Ethernet interface. This compact module is completely transparent to the IEEE-488 system and does not require changes to customer software or LabView drivers. Configuration is performed by the instrument.

Applications

Cryogen-Free systems:

Proprietary cryocooler thermal signature removal offers the best control stability in the industry for cryocooler based systems.
Four input channels. Cryogen-Free systems often require more than two.

General purpose laboratory:

Four inputs support virtually every cryogenic temperature sensor offered by every manufacturer. Two thermocouple inputs are optional.
Stepless Constant-Voltage excitation offers the widest possible temperature range for a given sensor.
Dual control loops. Digital Signal Processing techniques extend control loop resolution to provide the best control stability and widest range in the industry.
Ethernet connectivity for ease of remote control. Significant upgrade over IEEE-488 or RS-232 based systems. Native LabView™ support.
Robust cryostat protection controls.
Complete instrument configurations may be saved and instantly restored.

Superconducting Magnets:

Constant-voltage sensor excitation extends the high and low temperature range of sensors normally used in high magnetic fields.
Cryogen-Free magnet systems often require more than two inputs.

Data Acquisition / Computer control:

Ethernet interface in addition to IEEE-488 and RS-232. Ethernet allows the simple and inexpensive connection of many instruments to a Local Area Network. It is directly supported by all data acquisition software packages including LabView™.
Robust implementation of the IEEE-488.2 SCPI command language facilitates system software development.
Remote command language is identical across the entire product line, therefore ensuring your system software will not become obsolete.

CalGen™ and Cryo-Con™ are registered trademarks of Cryogenic Control Systems, Inc.
All other product and company names are trademarks or trade names of their respective companies.

Tel: (858) 756 3900 Fax: (858) 759 3515
Specifications subject to change without notice. ©Cryogenic Control Systems, Inc. 1998 - 2010.