e-Vision and e- LP101013.100 – 01 January 2004
MKS Instruments, Spectra Products
26
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.
7.3 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.
Ensure that the face of the analyser connector housing on the control unit butts up
to the analyser flange.