Version 1.1 (released 14 April 2021)
http://razorbillinstruments.com
Page 15 of 40
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Use with Andeen-Hagerling Bridges
When used with a capacitance bridge from Andeen-Hagerling,
the USB connection is not required, and noise will be lower if it
is not connected. If it is not connected, the front panel LEDs will
not illuminate.
The bridge should be configured with an average time of 7 or
higher. This triggers a “cold start” which is required if the
measured capacitance changes a lot of if the parasitic capacitance
of the cables changes. In future firmware versions, it is possible
that using the sample switch output will trigger a cold start, in
which case this will no longer be necessary. Contact Andeen-
Hagerling for further details.
TECHNICAL DISCRIPTION
The multiplexer contains two identical relay banks, these are
intended simultaneously switch the high and low measurement
arms of a capacitance bridge, LCR or similar measurement
instrument. Each of these relay banks consists of four BNC
connectors that can be either grounded or connected to the COM
terminal in the corresponding bank. The layout is illustrated in
Figure 3.
Grounding Notes
The analogue grounds for the High and Low relay banks are
internally connected to the case. This arrangement improves
electromagnetic emissions and ensures ground is provided to all
cable shields irrespective of other attached equipment. When
other attached devices also ground the cable shields, there is a
possibility of ground loop noise being introduced. Testing with
an Andeen Hagerling 2550A in a typical lab environment did not
show any reduction in performance with this arrangement, but
the analogue grounds have the potential to be isolated from each
other and from the case ground should this be necessary. To
isolate the analogue grounds, open the upper case and remove the
