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Hot tips for coldheads: five industry professionals share their secrets of success

by Philip F. Jacobus, CEO | September 05, 2015
From the September 2015 issue of HealthCare Business News magazine

9. Clean any strainers or filters in the water circuit regularly to ensure good consistent water flow at the OEM-specified rate
10. Ensure that your compressor is running all the time, 24/7.

Sean Mykleby suggests checking the helium levels along with the magnet pressure, and recording the stats in a log every day. This will help you to track trends and more readily notice any deviation from those trends, thereby potentially getting a warning before serious problems occur. He also suggested that for GE magnets, to take the RUO and re-condenser temps and log them as well. Sean agrees that chilled water temps and water flows are a great indicator of the functionality of the chiller, and a good chiller will extend the operational life of the coldhead and compressor.

Chris Matthews also suggests keeping a log. But he suggests monitoring and logging the compressor and chiller hours. He also suggests checking oil and gas lines for contamination using a black light. According to Chris, it’s a good idea to check the magnet turret for ice or heavy condensation — both indicators of a refrigeration problem. Jim Beier suggested relying on personnel to check the heater duty cycle (HDC) on the magnet. Most magnets have an internal heater.

Without proper control, the coldhead will try to drive the magnet pressure down. The magnet monitoring system will monitor the vessel pressure and send electrical current to the heater whenever the pressure gets too low. The heater will turn on and boil some helium, increasing the vessel pressure. The ratio of on/off of the heater is called the “heater duty cycle.”

Most magnets record the duty cycle. If you download it, you should see a steady state over time. If the system starts to fail (it takes six to eight weeks from the start to a complete failure) the duty cycle will eventually fall to zero. On GE magnets, the duty cycle is anywhere from 20-30 percent. When the system starts to deteriorate, the duty cycle will decrease, and when it hits zero, then the magnet pressure will start to increase. The HDC gives you advance notice, whereas the other, more obvious symptoms show up after the system has failed completely.

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