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.
HV card rack extender board
Voltmeter with 2 clip leads
Potentiometer adjustment tool
72-030 Calibration procedure
- Turn off the card rack power
- Extend the 72-030 neutralizer card (located in the card rack)
- Connect the DVM across R59 / E6
- Make sure that the filament cable is connected to the neutralizer on the system
- Turn on the card rack power
- Turn on the 147 PC Interface unit
- Open AugerScan software
- Turn on the neutralizer in AugerScan
- Monitor the target current with a picoammeter and a +90V bias
- 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.
- 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.
- 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.
- 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 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.