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How do I calibrate autonulling?

Download USB Programmer from Software Downloads

To check these values, plug in the USB2000+, startup USB Programmer, then click on the USB2000+ serial number that appears. On the right hand side you will see all the configuration information that is displayed in the EEPROM. Near the bottom there will be a line called “Autonulling Information”. This should read “Disabled, Disabled, xxxxx, 32000” where xxxx is some value in the 10000 – 20000 range. Basically the first value is the numerical baseline value and the next value is the numerical full scale saturation (always from 27000 to 32000 for a USB2000+). Basically the hardware subtracts the baseline value off of every ADC reading.  If that result is greater then the full scale range, it limits it to the full scale range. Thus the values the hardware transmits up are 0 – 27000 to 32000. The application software then scales the values to 0-65535 (full 16 bit).

If your values are “Disabled, Disabled, 65535, 65535” or “Disabled Disabled 0, 65535” then the values are defaulting and need to be reset.

To reset the values, follow these steps:

  1. Press FILE -> UNLOCK FEATURES… and enter UNLOCKALL
  2. Close down and restart the USB Programmer.
  3. Click on the USB2000+ Serial number on the left hand pane Double Click on the Autonulling Information on the right hand pane
  4. Set the baseline to 0 and the full scale range to 65535–Press OK. This effectively disables the autonulling.
  5. Press Save All Values
  6. Start OOIBase32 or SpectraSuite
  7. Create a dark condition for the USB2000+ and set the integration time to 4ms Record the dark level (typically 10000 – 20000 counts)
  8. Close down SpectraSuite
  9. Go back to the USB Programmer Double click on the Autonulling field. Subtract 500 off the value from step 9 and enter it in the baseline field.
  10. Enter 27000 up to 32000 (play with this value) in the Full Scale saturation field.
  11. Press OK Press Save all values Start SpectraSuite and the baeseline should be at ~1000 counts
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