e-Vision and e- LP101013.100 – 01 January 2004
MKS Instruments, Spectra Products
25
7.2 Ohmmeter analyser checks
There are a number of circumstances when carrying out some simple checks with
an ohmmeter can be worthwhile. If you suspect a failed filament or want to check
for shorts following some maintenance, performing some simple checks can save a
great deal of time.
In carrying out these checks, we can legitimately accept two ranges of meter
readings as possibly acceptable and anything outside these ranges as being a
definite fail. Any readings less than 1 ohm we can take as a short and any reading
above 5 Meg Ohm (5x10
6
ohms) as being open circuit. The following assumes that
the analyser is still on the vacuum system and goes through all the possible tests.
Tools required:
Ohmmeter with leads
Please refer to Page 31 for analyser pin numbers.
1. Attach a meter lead to pin 1 of the analyser feedthrough.
2. Connect the other lead to the analyser flange, you should read a short circuit. If
not, you have either a serious problem, or more likely a faulty meter/meter leads. If
after checking your meter, an open circuit still exists, contact your nearest MKS
Spectra service center for advice.
3. Move the lead from the flange and connect to pins 2 to 12 on the analyser
feedthrough in turn. Each one should give an open circuit. If not, you have a short
to earth.
There are two types of short to earth, an internal short between one part of the
analyser and an earthed part of the analyser, or more commonly, a short between
part of the analyser and the vacuum chamber.
In either case, remove the analyser from the vacuum chamber and repeat the test.
If the result is the same, then you have an internal short and should contact your
local MKS Spectra facility for advice.
Otherwise, you have a short to the vacuum chamber, check the dimensions of the
vacuum chamber around the quadrupole analyser, or try refitting the analyser in a
slightly different orientation.
Repeat the ohmmeter test before pumping down the vacuum chamber. Remember
that the ion source gets very hot during operation and the stainless steel
components will expand slightly. Sometimes a short will only develop when the
analyser has been run for a while and is up to temperature.