The Montana Instruments compressor is a variable speed compressor that is controlled by the software during the cool down. Having variable speeds increases the time between maintenance and allows the user to manipulate the speeds to run experiments optimally. In automatic cool down mode the compressor variably changes speeds as the temperature drops. If the target temperature set point is below what the system can achieve, the system will continuously run in high power mode (25Hz/70Hz). If the target temperature set point is achieved by the system the compressor will switch into the normal power mode which is 22Hz/50Hz. If more optimal settings are outside of the automatic mode, the user can operate the compressor in manual mode by going into Manual Mode in the software interface. Four speeds are discussed below which will optimize your system for various parameters.
- Start-up speed, 14Hz compressor/70Hz cold head – this speed is run when the compressor is starting up. It is important to only start the Cryostation using this speed. Any other speed will trigger an under pressure error, in which the pressure in the helium hoses dips too low. Using this setting is also optimal for getting the highest temperature stability above 6K. If temperature stability at higher temperatures is important for your experiments, utilize this setting.
- Normal Speed, 22Hz compressor/50Hz cold head – this is the speed that the compressor runs at once it is at the target temperature. This is the best setting for achieving the lowest vibrations in the system. Since most customers are concerned about having the lowest vibrations possible, this is the speed that is used in automatic mode at target temperature.
- High Power, 25Hz compressor/70Hz cold head – this speed offers the highest cooling power. If you are trying to get the lowest temperatures possible, continue to run the compressor at 25/70. The compressor only runs at 25/70 during automatic mode while it is actively cooling, but once the target temperature is reached, it switches to a lower cooling power. If your application demands the lowest possible temperature, run the compressor at 25/70 by setting the compressor mode in manual mode or setting the target temperature below what the system can achieve.
- Standby, 14Hz compressor/40Hz cold head – when not actively using the Cryostation, the system can be placed in standby mode. This speed uses the lowest amount of power. There is no PID feedback in standby, but once switched out of standby the PID will turn back on. This setting can be used during times when not actively running experiments, but where a full warm-up and cool down cycle is not desired for sample preservation or time constraints. If operating at higher temperatures, standby/low power is used. Be sure to monitor the pressure to ensure that the pressure does not get too high. Ideally, stage 1 should be below 90K to preserve the vacuum. If the vacuum starts to creep up, a higher cooling power may be needed and more power on the platform or user heater to achieve the higher temperature.
Below is a chart which summarizes the above.