Cirrus SP101013.111 – 10 October 2012
MKS Instruments UK Ltd., Spectra Products
45
8.4 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 34 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.
