A system was designed to automate cryogenically cooled low-noise amplifier systems used in the NASA Deep Space Network. It automates the entire operation of the system including cool-down, warm-up, and performance monitoring. The system is based on a single-board computer with custom software and hardware to monitor and control the cryogenic operation of the system. The system provides local display and control, and can be operated remotely via a Web interface.
The system controller is based on a commercial single-board computer with onboard data acquisition capability. The commercial hardware includes a micro-processor, an LCD (liquid crystal display), seven LED (light emitting diode) displays, a seven-key keypad, an Ethernet interface, 40 digital I/O (input/output) ports, 11 A/D (analog to digital) inputs, four D/A (digital to analog) outputs, and an external relay board to control the high-current devices.
The temperature sensors used are commercial silicon diode devices that provide a non-linear voltage output proportional to temperature. The devices are excited with a 10-microamp bias current. The system is capable of monitoring and displaying three temperatures.
The vacuum sensors are commercial thermistor devices. The output of the sensors is a non-linear voltage proportional to vacuum pressure in the 1-Torr to 1-millitorr range. Two sensors are used. One measures the vacuum pressure in the cryocooler and the other the pressure at the input to the vacuum pump. The helium pressure sensor is a commercial device that provides a linear voltage output from 1 to 5 volts, corresponding to a gas pressure from 0 to 3.5 MPa (≈500 psig).
Control of the vacuum process is accomplished with a commercial electrically operated solenoid valve. A commercial motor starter is used to control the input power of the compressor. The warm-up heaters are commercial power resistors sized to provide the appropriate power for the thermal mass of the particular system, and typically provide 50 watts of heat.
There are four basic operating modes. “Cool” mode commands the system to cool to normal operating temperature. “Heat” mode is used to warm the device to a set temperature near room temperature. “Pump” mode is a maintenance function that allows the vacuum system to be operated alone to remove accumulated contaminants from the vacuum area. In “Off” mode, no power is applied to the system.
This work was done by Michael J. Britcliffe, Theodore R. Hanson, and Larry E. Fowler of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47246
This Brief includes a Technical Support Package (TSP).
Automated Cryocooler Monitor and Control System
(reference NPO-47246) is currently available for download from the TSP library.
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Overview
The document outlines the development and functionality of an Automated Cryocooler Monitor and Control System created by NASA's Jet Propulsion Laboratory (JPL). This system is specifically designed to enhance the operation of cryogenically cooled low-noise amplifier systems utilized in the NASA Deep Space Network (DSN). The DSN operates over 40 such systems, which are critical for the performance of large aperture antennas.
Traditionally, the operation and maintenance of these cryogenic systems required skilled technicians to manually monitor performance and conduct cooling and warming procedures. The new automated system significantly improves efficiency by allowing remote monitoring and control, thereby reducing the mean time to return to service by a factor of two. This automation is achieved through a single board computer that integrates custom software and hardware for monitoring and controlling the cryogenic operations.
Key features of the system include the ability to monitor operating temperatures, helium pressure, and vacuum pressure, which are crucial for predicting potential failures. The system can detect mechanical wear of seals in the Gifford McMahon (GM) cryocoolers, which is a common failure mode. By monitoring these parameters, maintenance can be scheduled proactively, enhancing system availability.
The system operates in four basic modes: "Cool," "Heat," "Pump," and "Off." In "Cool" mode, the system commands the cooler to reach normal operating temperatures based on real-time data. "Heat" mode warms the device to near room temperature, while "Pump" mode allows for maintenance of the vacuum system. The "Off" mode ensures no power is applied to the system.
The document also highlights the hardware components, including an LCD display, LED indicators, a keypad, and various input/output ports for data acquisition. The software, developed in a C-based programming language, includes algorithms for converting sensor outputs into usable temperature and pressure units, and for controlling the cooler and vacuum systems.
Overall, the Automated Cryocooler Monitor and Control System represents a significant technological advancement in cryogenic cooling applications, with potential uses extending beyond the DSN to areas such as electronic cooling, medical imaging, and cryopumps. This innovation not only streamlines operations but also enhances the reliability and efficiency of critical aerospace systems.
