Cirrus SP101013.111 – 10 October 2012
MKS Instruments UK Ltd., Spectra Products
4. Move the meter lead from pin 1 and attach it to pin 2 of the analyser feedthrough. Connect the
other lead to pins 3 to 12 on the analyser feedthrough in turn. Each one should give an open circuit.
Now move the meter lead from pin 2 to pin 3 and check to pins 4 to 12. Proceed around the
feedthrough until all possible connections have been checked.
All the pins should show an open circuit to all other pins, EXCEPT pin 4 to pin 8 and pin 8 to pin 10,
which should show short-circuit as these are the filament connections.
If any of the pins read short-circuit to another pin, contact your local MKS Spectra service center with
the results of your tests and they will advise you how to proceed.
8.5 Checking filaments
Filament status is constantly monitored by the control unit and the operating software. This is achieved
by measuring the flow of electrons emitted by the hot filament, referred to as the emission current,
flowing to the ion source cage.
This is normally maintained at a fixed value of 1mA. The current flow through the filament is increased
until the value of emission current is reached. If, however, the control electronics reaches the limit of
its filament current supply capability and the emission current has still not reached 1mA, a filament fail
condition will exist.
In the vast majority of cases, this will be due to a blown filament, more correctly described as an open
circuit filament. There are other conditions, such as a heavily contaminated ion source, which will
result in a filament fail condition when the filament is not open circuit.
If you suspect a blown filament, carry out the following test before removing the analyser from the
vacuum system.
Connect meter lead one to analyser feedthrough pin 8, which is the common connection to both the
filaments.
Connect the second meter lead to pin 4 (Filament 1). You should read a short-circuit.
Now connect the second meter lead to pin 10 (Filament 2), again your meter should indicate a short-
circuit.
If either or both filaments are blown, the meter will indicate an open-circuit and the filaments will need
to be replaced.
If the meter reading suggests that the filament is good but the control unit shows a filament fail, the
most likely cause would be a break down in electrical continuity.
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