Hp E1313/E1413 Guard Connections; Common Mode Voltage Limits; When To Make Shield Connections; Noise Due To Inadequate Card Grounding - HP E1313A Manual

HP E1313/E1413
Guard Connections
Common Mode
Voltage Limits
When to Make
Shield Connections
Note

Noise Due to Inadequate Card Grounding

HP E1313/E1413 Noise Rejection

402 Wiring and Noise Reduction Methods
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The HP E1313/E1413 guard connection provides a 10 KW current limiting
resistor between the guard terminals (G) and HP E1313/E1413 chassis ground
for each 8 channel SCP bank. This is a safety device for the case where the
Device Under Test (DUT) is not actually floating, the shield is connected to the
DUT and also connected to the HP E1313/E1413 guard terminal (G). The 10
KΩ resistor limits the ground loop current, which has been known to burn out
shields. This also provides 20 KΩ isolation between shields and between SCP
banks which helps isolate the noise source.
You must be very careful not to exceed the maximum common mode voltage
referenced to the card chassis ground of æ16 volts (æ60 volts with the
HP E1513A Attenuator SCP). There is an exception to this when high
frequency (1 kHz - 20 kHz) common mode noise is present (see "HP E1313/
E1413 Noise Rejection" later in this appendix). Also, if the DUT is not
grounded, then the shield should be connected to the E1313/E1413 chassis
ground.
It is not always possible to state positively the best shield connection for all
cases. Shield performance depends on the noise coupling mechanism which is
very difficult to determine. The above recommendations are usually the best
wiring method, but if feasible, experiment with shield connections to determine
which provides the best performance for your installation and environment.
For a thorough, rigorous discussion of measurement noise, shielding, and
filtering, see " Noise Reduction Techniques in Electronic Systems" by
Henry W. Ott of Bell Laboratories, published by Wiley & Sons,
ISBN 0-471-85068-3.
If either or both of the HP E1413 and HP E1482 (MXI Extender Modules)
are not securely screwed into the VXIbus mainframe, noise can be
generated. Make sure that both screws (top and bottom) are screwed in tight.
If not, it is possible that CVT data could be more noisy than FIFO data
because the CVT is located in A24 space, the FIFO in A16 space; more
lines moving could cause noisier readings.
See Figure F-1 for the following discussion.
Appendix F