Auto exposure time

vas
vas
in Instrumentation and Mass Spectrometry
<p><span>Hi,</span></p><p></p><p><span>I am using acuity uplc with PDA .Recently obseved so many messages in UPLC logs as ''Auto exposure time to low'' some times and ''auto exposure time to high'' some times. what this problem and what is auto exposure time.Please suggested me.</span></p><p></p><p></p><p></p><p><span>Thanks,</span></p><p><span>Vas</span></p>

Answers

  • lizh
    lizh

    Hello:

    The autoexposure time is the time taken to scan the diodes and save a reading. These readings occur in milliseconds and then are averaged to become your data point depending on your data acquisition rate. It is usally the exposure time for the diodes to get enough light to record a signal across the wavelength range.

    A long exposure time would indicate a highly absorbing mobile phase, an old lamp, a dirty flow cell or a long data acquisition rate (set in the instrument method).

    So a short exposure time is usually the one that you want, indicating that the lamp has plenty of energy.

    For a given mobile phase and set of samples the exposure time should not vary. This is a great diagnostic.

    Are you setting exposure time manually, as it is better to allow "autosexposure" to be enabled.

    Can you send a chromatogram and noise measurement associated with one of your messages?

    many TX

    Liz

  • lizh
    lizh

    Hello again:

    Here is further clarification from the support team. They are suspecting that you should note when these messages are occurring, if they happen prior to the system being truly equilibrated they could be less significant. If not let us know.

    Autoexposure is the time in milliseconds that the detector determines is necessary to expose the photodiode array to the light for optimum detection based on the current contents of the flow cell. When the background of what is in the cell is high the auto exposure time increases to compensate for a lack of light to prevent a loss of signal.The opposite occurs when the background of the cell contents becomes less, so the exposure time decreases. The reason the customer is seeing these messages is basically due to changing conditions in the background of the cell contents or the light reaching the photodiode array as a result. This is one of the reasons we suggest starting the flow and reaching a stable condition of background in the cell prior to turning on the detector. By letting the background contents in the cell reach stability before turning the detector on you allow for the detector to establish the correct auto exposure and reduce the frequency of these messages.

    Best regards,

    Liz

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