Discussion Category: Centrifuge
Beckman Optima TL centrifuge
Does anyone know what the ohm's value of the thermistor ring (temp sensor) should be at room temp or at 0 degrees? The centrifuge I'm working on just shows a horizontal dash where the temperature should be, and the temp diagnostic flashes on the control panel.
I believe that you're looking at the problem incorrectly. If you have dashed line instead of numbers then you probably either have an outright failure of the sensor or more likely, a connection problem. I never actually had a sensor fail but I did experience connection issues from time to time. Check your connections carefully and then please post your results. Remember, all of the molex connectors only had crimps on the wires. Sometimes the pins actually needed to be soldered to the wires to fix some of these problems.
Thanks for your reply.
I will double check the connections.
I compared the ohm's with another thermistor ring from a different optima centrifuge and they are the same, around 900 ohms at room temp.
I believe I have continuity from the two pins where the sensor connects to the thermal electric board, all the way up to pin 4 of chip U27 and ground. U27 is a DG409DY. I also found that pin 7 of that U27 is shorted to ground, which, I don't think it should be. That may be my problem.
You appear to have done all of the necessary check in that you know the thermistor is good and you traced the connection out all the way to an individual chip on the board. I'm not sure what the chip configuration is but if its a 14 pin chip then pin 7 would most likely be ground, unless it's an op amp or other specialty chip. Since I don't know the account, is there any possibility of swapping out the boards? I really don't like doing that but sometimes it's all you have to work with.
I finally received the new DG409DY chip and replaced what I thought was a bad U27, but no change. I still have a horizontal line in the tenths place of the temperature display. Very frustrating without a schematic. Any help would be greatly appreciated from anyone.
To anyone concerned,
I called a local lab instrument service company that is very knowledgeable about Beckman equipment to take a look at the Optima TL centrifuge. The service tech did a calibration on the temp sensor and all is fine now. Without a service manual, I would have no way of getting into the diagnostic/calibration mode. It guess it could be possible that chip U27 was bad, but the centrifuge would still need to get calibrated after replacing. Maybe try calibration first if this problem happens to you.
Lance, I'm pleased that you apparently got your problem resolved. You should remember, however, that ALL Beckman Coulter ultracentrifuges are designed to only MAINTAIN rotor temperatures. They are NOT designed to be the primary means of cooling a rotor down to the temperature that you may want to run the rotor at unless you are cooling it down overnight. This is especially significant with the benchtop ultracentrifuges. Many individuals also do not understand the implicit relationship with having a completely functional vacuum system. By this I mean that the vacuum system is capable of pulling the chamber vacuum down to 1 micron. Anytime the vacuum is greater than 100 microns, there is enough air molecules in the chamber to give erroneous temperature readings and up until about 450 microns you can actually get some thermal heating effects in the chamber.
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