University of Ottawa NMR Facility Web Site

Please feel free to make suggestions for future posts by emailing Glenn Facey.



Thursday, June 17, 2010

Heat Dissipation in Bruker AVANCE Spectrometers

It is very important that an NMR spectrometer operate within a fixed temperature range. To control the temperature, many units within the console are equipped with cooling fans which must be kept in good working order. Failure to do so will shorten the life of the spectrometer and cause instability or malfunctions. In the Bruker AVANCE series of spectrometers, the SGU (Signal Generation Unit) boards are particularly sensitive to temperature. Each SGU houses a DDS (Direct Digital Synthesizer) containing numerically controlled oscillators which regulate rf frequencies and amplitudes. The DDS is normally temperature regulated at 55° C to insure stability. Both the SGU board temperature and DDS temperature can be measured either with the "UniTool" (AVANCE and AVANCE II) or web based tools (AVANCE III).

After years of service, two of our Bruker AVANCE spectrometers were running very warm. Using "UniTool" to check the temperature of the SGUs revealed that the board temperatures averaged 58° C! The DDS temperatures were all >55° C and not regulated. The air filters in the console doors were removed and cleaned and all eight fans of the AQS unit, housing the SGU's, were replaced on each spectrometer. After a day for the instruments to come to a thermal steady state, the SGU and DDS temperatures were again measured. The SGU board temperatures averaged 49°C. The DDS units in three of the five SGU's were now regulated properly at 55°C. The other two were still > 55°C and unregulated. In an attempt to lower the temperature further, the backs of the spectrometers were removed and again the instruments were allowed to reach a thermal steady state over a 24 hour period. The SGU and DDS temperatures were measured again. This time the SGU board temperatures averaged 38°C and all five DDS units were regulated properly at 55°C. The SGU temperatures in our AVANCE II and III spectrometers (with backs on) did not exceed 40°C and the DDS temperatures were regulated properly.

Although this may not be recommended by Bruker, I now run our AVANCE spectrometers with the back panels removed.

8 comments:

Bernie O'Hare said...

Hi Glenn,

Are there any empty slots in your AQS rack that are open? Meaning that there is an open gap in the AQS rack that is not covered by the panel slots thst fit into the gaps. Sometimes these open gaps can cause these types of heat problems because the cooling air is escaping through these open slots instead of being routed through the AQS appropriately. If there are these open slots you may want to get the covers for them and see if that makes any difference.

Glenn Facey said...

Hi Bernie,

All slots on the AQS racks are full and the airflow seems good. On our two bay AVANCE the back panel has only one fan to help vent air. I wonder if maybe this is not enough. On our one bay AVANCE the back panel has no fans.

Glenn

Anonymous said...

we always keep the back panels removed. So don't be afraid Bruker doesn't recommend it ;)
Moreover, the fans tend to die after a few months due to the constant operation of a spectrometer. So you better keep an eye on them ;)

Thierry said...

On previous generations of instruments (Bruker already, some 30 years ago), my dad used to take the electronic components out of the frame and align them on a separate open shelf, with a fan blowing on them. It was a weird looking setup, but it worked.

Anonymous said...

Hi! Glenn:

How do you clean the air filters, it cost hundred of dollars to buy them from Bruker.

Glenn Facey said...

Dear Anonymous,

I use a vacuum cleaner. I do believe however that replacing the filters would be a better option.

Glenn

Guang said...

Hi Glenn,

What about the temperature regulation of the older PTS Quartz Oscillator driven frequency synthesizer? How do I know the temperature inside it?

Glenn Facey said...

Guang,

I'm not sure how to monitor the temperature in an older PTS synthesizer or indeed if it is important to do so.

Glenn