The CryoTel® GT is a free-piston Stirling cryocooler manufactured by Sunpower, Inc., a world leader in free-piston Stirling cryocooling. This precision instrument is designed for various applications requiring cryogenic temperatures, offering robust performance with specific handling and operational precautions. The device is controlled by a Gen II v1.0.0 controller.
Function Description:
The CryoTel® GT operates as a free-piston Stirling cryocooler, generating cryogenic temperatures by means of an oscillating piston within a pressure vessel. It is designed to cool an attached object or system to a desired low temperature, typically operating best in an insulated vacuum environment to prevent heat loading from convection or condensation. The controller manages the cooling process by measuring the cooled object's temperature via a sensor and adjusting the cooler's power ramp-up to maintain a set point temperature. The device can operate in either temperature control mode, aiming for a specific target temperature, or constant power mode, maintaining a user-commanded power output.
Important Technical Specifications:
- Dimensions:
- Length with balancer: 260 mm (10.2 in)
- Length without balancer: 217 mm (8.5 in)
- Diameter: 83 mm (3.3 in)
- Mass: 3.1 kg
- Cold Tip: Features a ¼"-20 threaded hole for mounting equipment.
- Temperature Sensor: Utilizes a Lakeshore PT-111 platinum RTD or equivalent, packaged in a copper disk for consistent size, shape, and wiring.
- Power Input: The controller requires a 48VDC power outlet.
- Power Output: The maximum power draw by the controller is approximately 300 WE.
- Minimum Load Requirement: Requires a minimum loading of 6 Watts for proper operation; if not met, the stabilized temperature may fall below 77 K.
- Vacuum Requirement: Operates best in an insulated vacuum of 10⁻⁴ Torr or better.
- Heat Rejection: Options include a water jacket (requiring 15mL/s or 0.24 gallons/minute water flow), copper fins (requiring a fan with 100 cubic feet per minute (1.6e-3 m³/min) air through-flow), or a conducting solid.
- Serial Communication: RS-232 interface with a Baud Rate of 4800, no flow control, 8 data bits, and 1 stop bit.
Usage Features:
- Mechanical Mounting: The cryocooler can be attached to an external mechanical structure using M4 threaded holes on the outer diameter of the transition and end plate, or M3 threaded holes on the stainless steel plate of the heat rejection ring for vacuum flange attachment.
- Heat Load Attachment: Equipment can be mounted to the copper cold tip using the ¼"-20 threaded hole. Specific force limits apply to the cold tip (e.g., cantilevered force < 100 N when not in operation, < 30 N when in operation; vertical load < 300 N; torque < 16 N·m for cold finger, < 10 N·m for cold tip thread).
- Vacuum Environment: A customer-provided vacuum Dewar or cryostat is used to create the necessary vacuum. Flange connections can be sealed with O-rings and clamps for temporary use or welded for long-term vacuum without a pump.
- Temperature Control: A temperature sensor (Lakeshore PT-111 RTD) must be mounted to the object being cooled to enable the controller to measure and regulate temperature. Thermal grease or indium is recommended for optimal thermal conduction.
- Controller Operation:
- Startup Sequence: The controller performs a 7-10 second startup sequence to axially center the piston, then applies a 60 Hz AC voltage to initiate cooling.
- Control Modes: Can be set to maintain a constant target temperature (PID=2) or a constant power output (PID=0).
- Soft Stop Functionality: Allows for a controlled shutdown of the cryocooler, slowly ramping down power to minimize shutdown vibration. This can be initiated via a command or a digital input.
- Thermostat Mode: Enables an external thermostat to shut down the cryocooler when its circuit opens.
- Status Indicators: Two LEDs on the controller indicate operational status: a red LED for cool-down mode (not at setpoint) and a green LED when the cooler reaches its setpoint temperature within a defined band (default 0.5K). Digital Output 4 also goes high (5V) at setpoint temperature.
- Serial Communication: Commands can be sent via a terminal emulator program (e.g., Hyperterminal) to display or set various parameters such as temperature sensor value, target temperature, commanded power, control mode, soft stop mode, power limits, thermostat mode, temperature band, and password.
- Password Protection: Controller parameters can be locked or unlocked using a user-defined password (default: STIRLING).
Maintenance Features:
- Heat Rejection Maintenance:
- Water Jacket: If using a removable water cooling jacket, suitable thermal grease should be applied between the heat rejecter and the jacket and refreshed periodically. Air must be removed from the water jacket by flowing water through the system for several minutes and tilting the cooler if necessary.
- Copper Fins: If using copper fins, a fan and cylindrical shroud are recommended to direct airflow and ensure proper heat rejection. Electrical interlocks between the fan and controller are advised to prevent operation without cooling.
- Error Reporting: The controller reports errors through flashing LEDs (both red and green simultaneously) and via the
ERROR<CR> serial command, which returns a binary code indicating specific error types (e.g., Over Current, Jumper Error, Serial Error, Non-volatile Memory Error, Watchdog Error, Temperature Sensor Error).
- Error Resolution: For most errors, power cycling the controller is the first step. For wiring-related errors (Over Current, Temperature Sensor Error), checking connections is crucial. If issues persist, contacting Sunpower support is recommended.
- Factory Reset: The
RESET=F<CR> command can be used to restore all controller parameters to their factory defaults.
- Cold End Vacuum: For long-term applications without a vacuum pump, welding the cryostat to the CryoTel® vacuum interface is recommended over O-ring seals, as O-rings can corrode and become brittle over time.
- Shutdown Procedure: Before opening the vacuum, allow the cold tip to reach room temperature to prevent condensation and freezing. Applying a heat load during warming can reduce this time.
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