HPQ2-IP SP101009.102 – 10 October 2012
MKS Instruments, Spectra Products
28
7.4 Ohmmeter Analyser Checks
There are a number of circumstances when carrying out some simple checks with
an ohmmeter can be well worthwhile. If you suspect a failed filament or want to
check for shorts following some maintenance, a lot of time can be saved by
performing some simple checks.
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 35 for the analyser pin numbers.
7.5 Checking for shorts
1. Attach the first meter lead to pin 1 of the analyser feedthrough.
Connect the second meter lead to the analyser flange, you should have a short
circuit. If not you have a serious problem or more likely a faulty meter.
3. Connect the second meter lead to each of 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 basically 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
than you have an internal short and should contact your local Spectra facility.
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.
4. Attach the first meter lead to pin 2 of the analyser feedthrough. Connect the
second meter lead to each of pins 3 to 12 on the analyser feedthrough in turn. Each
one should give an open circuit. Now attach the first meter lead to pin 3 and check
to pins 4 to 12. Proceed around the feedthrough until all possible connections have
been checked.