A question was recently posed regarding the grounding conditions of a BNC type input. The shield or outer of a BNC cable or connector is not connected to the chassis or ground. What would happen if it was connected to ground?
Would the P8000 be potentially damaged if you were to do this?
There is no issue connecting the BNC or cable outer to ground on any P8000 input card.
If there was some potential source of large voltages or current you may want to use a resistor to make the connection to ground. This would ensure there is less chance of damaging the P8000. But we would suggest it is not necessary.
What is the advantage of connecting the BNC or cable outer to ground?
It is possible that in some circumstances noise can be present on a particular signal, this could be from a number of sources. For instance, poor grounding. In some cases the noise maybe mitigated by connecting the BNC or cable outer to ground.
It is good practise to understand the source of the noise and remove it rather than to try to mitigate its effects. For example if the power supply has a good quality ground then you should not need to make an input single ended.
What is the downside of connecting the cable or BNC outer to ground?
The downside of connecting the BNC or cable outer to ground is that the input is no longer differential, but single ended. Indeed, this is part of the reason that noise can be reduced by performing this action.
To understand the difference between differential and single ended inputs please see:
http://blog.prosig.com/2011/02/15/what-is-the-difference-between-single-ended-differential-inputs/
James Wren
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