72-030 Neutralizer Current limit procedure

After you replace the filament in the 04-085 or 04-090 neutralizer you may need to readjust the current limit on the 72-030 neutralizer board. The 72-030 provides the filament current and bias voltage to the neutralizer. This procedure shows you how to set the current limit on the 72-030 so that you generate enough electrons to neutralize the sample and also maximize the filament lifetime.

Tools Needed:

HV card rack extender board

Voltmeter with 2 clip leads

Potentiometer adjustment tool

72-030 Calibration procedure

  1. Turn off the card rack power
  2. Extend the 72-030 neutralizer card (located in the card rack)
  3. Connect the DVM across R59 / E6
  4. Make sure that the filament cable is connected to the neutralizer on the system
  5. Turn on the card rack power
  6. Turn on the 147 PC Interface unit
  7. Open AugerScan software
  8. Turn on the neutralizer in AugerScan
  9. Monitor the target current with a picoammeter and a +90V bias
  10. Turn up the Emission in the Augerscan Neutralizer dialog box to 20 to 23 mA while monitoring the DC voltage in millivolts across R59 / E6.
  11. There should be approximately 34 mV across R59 / E6 and you should also be able to see the end of the neutralizer glowing orange to white in the vacuum chamber.
  12. Set the Emission to 25 mA and if necessary adjust R48 / B6 so that you have 2 to 3 uA of target current.   Do not adjust R48 / B6 to exceed 36mV across R59 / E6. 36mV corresponds to 3.6 amps of filament current. The lower the filament current, the longer the filament lifetime.
  13. Turn off the card rack power and reinstall the 72-030 neutralizer card in the card rack.

Ideally, adjusting R48 for a value that provides a few uA of target current and with less than 36mV across R59 / E6 will result in the longest filament lifetime.

72-030 board extended
R59 current sense resistor
Measure voltage across R59 34mV corresponds to 3.4 amps of filament current

72-030 Neutralizer bias voltage notes

There are two revisions of 72-030 neutralizer boards.  The older original 72-030 has a bias voltage range of 0 to -12V.   The newer 72-030s have a bias voltage range of 0 to -24V.

You can tell the difference by two things.  First of all, U6 is a OP07 op amp on the older 72-030s, and it is a LM344H high voltage op amp on the newer 72-030s.  Secondly, there is a 5V to 15V power convertor on the newer boards, the older 72-030s do not have that power converter.

12V bias 72-030
24V bias 72-030