TLX temperature drops slowly

It sounds like you may have either a possible vacuum issue or there is a problem with the thermoelectric modules or control assembly. You state that it was previously working properly but now its not. Is there anything different going on with the centrifuge? Any dirt or dust accumulation around the chamber O'Ring that could be causing a vacuum issue. Do you let the centrifuge run for about 30 to 45 minutes with the vacuum pump running prior to an actual sample spin? It may not be in the operator's manual instructions but every service engineer knows that we needed to tell each and every customer to do this.

The vacuum problem is fairly easy to observe if that is indeed the problem. You need to go into the system information on the centrifuge by pushing the following key sequence: [ENTER], 411, [ENTER]. You should see a display that says "Vac" and then some numbers. If the numbers do not go down to 1 or very close to it then you may have a vacuum problem. The only issue with even looking at the vacuum system this way is that I have no way of knowing if or when the last time your vacuum system was checked or calibrated but there was a service memo that was put out that clarified the procedure for the calibration as many service engineers were not setting up the vacuum system and its readout correctly. Even if the readout displays properly you have no way of knowing if it is entirely accurate. Unfortunately, you need a vacuum calibration standard and the correct procedure to get it set up properly and I no longer have access to that procedure.

If the problem is with the Thermoelectric modules (TEM') then you will need to have the centrifuge serviced.

Don

Don,

Thanks a lot for the valuable information.  First, I inherited this unit from one of our colleagues when his lab moved about 6 months ago.  The unit was running fine then and I don’t recall that the temp ramped down slowly below ~8’C.  The description I gave was done with sample run soon after ‘vac’ sign off, ~2 min after door close.  I will try to wait 30-45 min after loading samples and see if it will run better.  

One question: I think I tried [ENTER], 411, [ENTER] a while ago but noting showed.  Did I do anything incorrectly? I was pressing the [Enter/Display] on the keypad, then 4,1,1, [Enter/Display] .  I’ll try again on Monday.

On Friday I tried to ramp the temp up from 10 to 36’C and it went up very quickly, probably about 3 minutes.  It seemed that the thermoelectric part was working reasonably ok.  I was thinking its slow cooling at lower temperature could be related to heat dissipation but my unit was >6” to side and back.   Still puzzled.

Thanks,

LanceH

Don,

I pushed the key sequence [ENTER], 411, [ENTER], but the display only flipped back to the set parameters for a few secs with the [ENTER/Display] key press. Nothing else displayed. Any ideas?

I checked and re-greased the O-ring, and let it sit 45 min after loading samples. The temp rose 1'c with a 50k spin which was better than before. However, the temp stayed there (6.8'C) and hesitate to drop. Any suggestions would be much appreciated.

LanceH

Lance, Sorry but I didn't realize that you don't have the CE version of the TLX. Therefore, the only way to check the vacuum is to remove the top cover. On the circuit board inside the top of the centrifuge, you will see a silver toggle switch that will allow you to get a vacuum reading. In order to remove the top cover, you must also remove the door handle. The two screws are VERY soft aluminum so you want to treat them carefully. Then, after removing the 6 hex screws on the side of the centrifuge, you should be able to slide the top cover forward and off of the centrifuge. If you see a silver interlock switch next to the power switch, pull it all of the way out. Otherwise, the centrifuge will not power up.

Start a test run and let it run for at least 30 minutes and then check the vacuum level by toggling the switch. You will have to hold it closed for around 10 seconds in order to get a valid reading. Continue to do this and by the time 45 minutes has gone by you should have a very low vacuum reading somewhere below 50 microns.

Also, the vacuum light goes out after a vacuum of 450 microns is reached. This is not a deep enough vacuum to provide good temperature control so the temperature readout will still be reflecting the temperature of the air molecules still in the chamber. After the vacuum gets to 50 microns your temperature readings will start to become more accurate. Please understand, the temperature of a rotor precooled to 4C will not change as rapidly as what the temperature readout indicates. It is just not possible for that to happen inside of the centrifuge with the vacuum running and the temperature control active.

Give it a try and get back to me.

Don

Don,

Thanks a lot for the information.  I opened up the unit and there were 3 toggle switches on the top circuit board.  From left to right -- there is a bigger one with red marks, I think it is spin related.  The middle one seems to be temperature control related.  The last one, which is near the back side of the machine, gave some reading at temperature section when toggled.  It seemed to be vacuum reading. 

I started a run without a rotor.  30 min reading was 18.3 (183?).  45 min reading was 16.0 (160).  The temperature reading was 5’C at 45 min.  Perhaps vacuum was not good enough. 

The inside of the machine had small debris of deformed foam from the under side of the cover, but otherwise clean.  I recall seeing a couple of this kind of particles inside the chamber the other day.  Maybe this is related to the vacuum problem.  I vacuumed the debris and cleaned the rails of the door.   I am sure the debris will accumulate over time.  Do you know if it is ok to remove the foam on the underside of the cover completely? 

The foam cover on the air intake side is also deforming.  I sort of want to remove it as well but not sure if it will do anything bad.

One more observation, I noticed that the clear tube on top of the vacuum pump was not connected to the port on the pump.  Didn’t recall if it was connected when I opened the unit.  Connected back anyway.

Thanks.

LanceH

Lance, Sorry that I couldn't recall that there was more than one switch on the circuit board.  It has been awhile since I had one of those opened up.  Your supposition about the vacuum readings is correct as to the vacuum level.  There is no way that 160 is a good enough level to maintain temperature.  What you need to do next is put a test run on the centrifuge and see what happenes with the vacuum level after 45 minutes.  It is perfectly OK to toggle the vacuum sensor switch with a run underway.  Just give it enough time for the reading to stabilize when you toggle the switch.

You can remove any and all foam from under the top cover of the centrifuge.  It is there for noise abatement but it typically just gets dried out and creates a mess everywhere including inside of the chamber.  Also, the clear tubing MUSt be in place on the vacuum pump because it is used to help remove excess moisture from the vacuum pump oil.  Also, make sure that the vacuum hose attached to the top of the vacuum pump is squarely down on top of the pump assembly.  If it is even slightly skewed it can effect the performance of the vacuum system.  Making sure that there is no debris sitting on top of the cahmber plate is also important as it doesn't take much to prevent the door from seating properly.  By the way, when was the last time that the vacuum pump and diffusion pump oils were changed?  Poor condition of the vacuum pump oil and/ or low levels in the diffusion pump can result in poor overall vacuum performance.

Please let me know how the vacuum performs during a normal test run.

Don

Don,

I started a 50k run at about 10 minutes after closing the door.  The vacuum reading was 220.  It read 186 at 30 min and 180 at 45 min.  It dropped to <170 when the the run stopped and rotor spin =0. 

I found  a piece of paper inside the machine.  The last oil change (shown as vac/diff oil was May 2008.  I don't know the exact history of the machine but it was not used much in the past few years.  I used to maintain X-ray generators so changing rough and diffuse pump oil shoudn't be a big deal, or should I call for a service?  I did try to wipe the underside of the door as far as my fingers can reach with kim wipes. 

In this process I found two things:

1. The rubber tubing going over the clear tube has a small crack.

2. Not sure if this is normal: The chamber was slightly tilted when the door was open.  There was a spacer holding the far side down a few mm.

Two images are attached below.

Thanks,

LanceH

Lance,  The crack with in the clear tygon hose is probably not big of a deal.  The cracks and positioning of the vacuum hoses is more than likely the source of your vacuum problems.  When the thin wall vacuum hose comes up out of either the vacuum pump or the diffusion pump, it must go straight up for at least an inch or two before going over to the other pump.  Otherwise, you get micro leaks around the vacuum hose ends and that will cause the kind of problem you are seeing.

Now, as to the refrigeration can being tilted, that could be indicative of even bigger problems.  The black spacers that are placed around the inside of the vacuum chamber that hold the refrigeration can in place are there by design.  They are used to ensure even contact pressure between the bottom of the can and the thermoelectric modules on the heatsink underneath the can.  If one of those is broken then you will also have problems with cooling as there will be uneven pressure and contact between the two items I mentioned.  If this happens, you could then get uneven heating or cooling from one of the three modules.  In fact, one of them could eventually draw too much current and burn out which will completely shut down the cooling.  The tilt is not a good thing and the fact that the centrifguge hasn't been serviced in over 5 years is also an issue.  If the centrifuge was tipped on its side at all while moving, vacuum pump oil may have moved over into the diffusion pump which will definitely cause serious vacuum issues.  I'm sure that with your previous experience you can handle the maintenance work but getting everything apart and especially servicing the vibration mounts that are part of the drive assembly may be more than you are willing to deal with.  There are more than a few tricks that we were taught during training classes relative to servicing a tabletop ultra centrifuge.

Finally, whether or not you choose to undertake the maintenance is up to you but it sounds as if you might benefit from factory service on it and just kind of watch what the engineer does as part of the process.  Especially about getting the vacuum and diffusion pumps out of the centrifuge easily.  Again, there are some tricks that make the process a little easier than it might appear.  And whatever you do, DO NOT emphsize what kind of background you have as that will tend to put the engineer on his guard as to how much he might share with you so that you might be able to deal with basic maintenance again in the future.

Don

Don,

Thanks much for the comments.  After the test run yesterday, I shut off the machine for ~1.5hrs.  When I turned it back on, the vac light stayed off when everything started.  This is probably an indication that the vacuum chamber was reasonably sealed, and the vacuum being not low enough had more to do with the pumps/pump oil. 

You are right that it'd be a good idea to get a service engineer to check things out. I was only doing the X-ray machines as a senior lab member, not professionally, and that was long time ago.  There is no way I can maintain this machine without clear instructions/manuals.   I know a Beckman service call is going to be very expensive, but we'll probably have to squeeze it out of our already reduced research budget anyway. 

One more question -- regarding the spacer/hook holding the refrigeration can, since I could only see one hook engaged.  Assuming that the other two are still intact, would it be possible to press down the other sides carefully to get them engaged, or the whole thing has to be taken apart.  Just curious.

Thanks,

LanceH

Lance,  You should notice that there are hex screw heads around the top of the chamber coinciding with the positions of the black spacers.  Sometimes, the latching spacers get twisted around such that they are pointing backwards from the chamber.  What you need to do is loosen the set screwto see if the black plastic spacer rotates around into view.  Try it first on the one that you can see so that you see how the tie downs work because that is what the black plastic pieces are, chamber tie downs.  If they are still there, merely resecure them.  Run the set screw down just so it is below the level of the top camber plate.

The overall vacuum issue is probably due to the poor condition of the oils as well as the the positioning and cracks in the vacuum hose(s).  It really doesn't take much vacuum to keep the door closed.  What that is telling you is that the system is relatively tight in that it is holding some vacuum.  There is a check valve inside of the vacuum pump that prevents complete loss of vacuum when it shuts off from loss of power and that's why you still have a vacuum.

The entire service process shouldn't take more than 2 hours or so, at least that's how long itwould normally take me to do a complete preventative maintenance service call.  I don't know what Beckman's current hourly rates are but they were at $320/hr when I retired 18 months ago.  Please feel free to get back to me with any other issues you might have.  The quick way is my cell (717) 450-6954.

Don