The "He recondenser" contoller is designed from industrial components and allows to condense as much helium as possible while maintaining the pressure just above the atmospheric pressure in the liquid helium bath of a cryostat or cryomagnet. The pressure in the liquid helium bath is measured relative to the atmosphere pressure with a relative sensors from GE or other companies. The heating power delivered inside the liquid helium bath or to the second stage of the cooler is easily managed with a process controller (Eurotherm model 3504).

Intuitive interface

The unit measures and displays permanently the liquid helium bath pressure with a vertical bar graph and large digits in hPa which are visible quite far away from the cabinet. The output heating power is displayed with a horizontal bar graph in % and a number in mW.

The user can changed the helium bath relative pressure setpoint at anytime and the controller adapts the output heating power automatically. Alarms are set using high and low levels and the unit applies PID parameters to regulate the pressure. In order to display the right heating power delivered to the bath, the user can enter a lead wire compensation in Ohms.

If needed, it is also possible to control manually the ouput heating power in mW.

Easy settings

The He recondenser is calibrated in a very few steps:

• prepare the cryostat with liquid helium
• enter the Settings mode
• check the high and low level values
  
• set the lead wire compensation value
• quit the Settings mode
• enter a pressure setpoint, e.g. 10 hPa
  

The PID parameters can also easily be modified from the Settings menus according to the user wishes.

Full remote control

Computer control via RS-485 and Ethernet is available. All parameters can be read and set, even the lead wire compensation. The communications are based on the Modbus communications protocol which has become a de facto standard in industry. We provide a Modbus XOP and a Procedure for controlling the level monitor with Igor Pro.