- 08/24/2018 – Obtained computer housing casing for free for control system build.
- 08/30/2018 – Completed soldering of instrumentation and control boards for cooling control and monitoring.
- 09/10/2018 – Mounted control boards to baseplate and started control system wiring.
- 09/15/2018 – Extended trial version of MegunoLink obtained for preliminary control system development and software qualification.
- 09/24/2018 – MegunoLink software license purchased for full development of the control system.
- 09/28/2018 – Soft interlock relay board functionality tested and verified.
For the high vacuum test stands being built at Applied Ion Systems, monitoring, data logging, remote and local control, as well as interlocking are critical for the safe and reliable operation of the experimental systems. A low-cost control system has been designed and built for handling the control and monitoring of these subsystems. The three primary subsystems that are controlled and monitored during standard operation include the closed loop peltier chilled diffusion pump cooling system, the low vacuum subsystem, and the high vacuum subsystem.
The control system is based around the Arduino Mega microcontroller. Various sensor inputs from each of the subsystems are conditioned through the appropriate circuitry, and sent to the microcontroller. Depending on the subsystem and desired parameters, interlocks are established.
For the closed-loop cooling system, a total of ten inputs are presently employed – six k-type thermocouple probes in critical areas throughout the cooling loop, as well as three flow monitors (one for each loop in the cooling system), and a dual ambient temperature/humidity sensor. The thermocouples provide critical performance feedback of the cooling system during operation, and allow the operator to closely monitor thermal conditions of each of the loops to ensure proper cooling and chilling of the critical water-cooled components is being maintained. System performance can be related to ambient conditions if needed, and effects of ambient temperature and humidity on system performance can be observed for reference. Should the temperature in any part of the system exceed a designated operational limit, power to the high vacuum pump will be shut down.
The flow meters are also used for safety interlocking of power to the diffusion pump, in the event of no-flow or low-flow conditions. In addition, the flow meters also provide feedback necessary for controlling the pumping speeds of the three pumps in the cooling system for adjusting flow rates to the required levels, as well as optimizing thermal response of the system.
The cooling system includes numerous outputs, primarily for engaging and interlocking power to critical subsystems. Outputs are controlled through the 16 channel relay board which switches power on and off to the various pumps, chiller modules, fans, vacuum pump power. This allows for both manual control, as well as automated control for automated cooling and vacuum pumpdown sequences.
The low vacuum subsystem input takes data from the thermocouple vacuum gauge located in the roughing line and uses this for controlling power to the diffusion pump for both safety interlocking and automated pumpdown sequences. Once the rough vacuum has achieved the desired level, power to the diffusion pump through the roughing interlock can be enabled.
The high vacuum subsystem input takes data from the HPT-100 wide range pressure transducer located in the high vacuum chamber and uses this for critical interlocking of power to the high vacuum diffusion pump, as well as general process monitoring. Should the vacuum level exceed a critical point where operation of the diffusion pump becomes unsafe, power is disconnected from the diffusion pump through the relay board.
Hardwired interlocks are employed in the control system that run completely independent of the user interface software. DC and AC current sensors are used for every powered devices in the system (such as water pumps, fans, peltiers, vacuum pumps, etc.) These allow for automatic control of a separate set of several series relays used for protecting critical equipment such as the diffusion pump, and will automatically engage with detected current parameters to each part are outside of nominal operating conditions. This ensures that the system as well as the user are protected in the event of individual component failure. Signals from the current monitoring sensors are also sent back to the control system in parallel with the hardwired interlocks to provide alarm feedback, which is displayed on the user interface.
In addition to the physical control system sensors, circuitry, and microcontroller, a user interface has been developed for remote access, control, and monitoring in real time of the various subsystems. An interface using MegunoLink has been implemented to allow for bidirectional communication between the control system and the user interface. The program allows for easy and rapid development of an advanced user interface, displaying sensor data, data acquisition graphing, system controls, interlocks, and alarms. The system allows for automated data acquisition, as well as manual modes for individual component control and testing, as well as a fully automated mode, allowing for the entire cooling and high vacuum pumping sequences to be initiated with the single pres of a button, while integrating feedback from both hardwired and soft interlocks.
The entire control system, including all low-voltage power supplies for the controller, electronics, sensors, pumps, chiller, and fans, is housed inside of a re-purposed computer casing, which can be mounted to the side of the 80/20 test stand, or placed remotely with extended control cables. For the purposes of safely operating the system with high intensity pulsed power systems, EMF shielding will be employed with the system, which includes careful shielding of the entire structure in a grounded copper shielding mesh, critical controller electronics further shielded internally with proper EMF shielding, and high frequency ferrite chokes used on all inputs and outputs from the casing chassis. Additional shielding of control and monitoring cables may be necessary depending on the peak power and pulse parameters of the device in operation.