cabling mystery

[Fritz Oppliger]

To protect an analog signal we replaced plain ribbon cable with shielded
ribbon cable.
The shielding we connected to earth ground on ONE end. Now the humidity
reading is erratic. Switching back to plain unshielded ribbon and the
problem goes away. This defies all the rules in my book - What could I
be overlooking?
--
Fritz Oppliger

 

[John - KD5YI]

Fritz Oppliger wrote:

To protect an analog signal we replaced plain ribbon cable with
shielded ribbon cable.
The shielding we connected to earth ground on ONE end. Now the
humidity reading is erratic. Switching back to plain unshielded ribbon
and the problem goes away. This defies all the rules in my book -
What could I be overlooking?

Earth ground? Try connecting the shield to the circuit ground (common) at
one end. Then try the other end.

Good luck.

John

 

[Art]

Actually you may be inducing a ground loop signal by connecting one end to a
known 'earth ground'. This will tend to skew the information [create noise]
at the receiving end. As posted, try connecting one end to equipment
reference [ground] rather than the true 'earth ground'. Seen a lot of
problems in CCTV systems as a result of earthing the cable shields.
"John - KD5YI" <groups5munge@verizon.net> wrote in message
news:AuDde.8666$nN.7137@trnddc05...

Fritz Oppliger wrote:

To protect an analog signal we replaced plain ribbon cable with shielded
ribbon cable.
The shielding we connected to earth ground on ONE end. Now the humidity
reading is erratic. Switching back to plain unshielded ribbon and the
problem goes away. This defies all the rules in my book - What could I
be overlooking?

Earth ground? Try connecting the shield to the circuit ground (common) at
one end. Then try the other end.

Good luck.

John

 

[Fritz Oppliger]

The aim was to reduce the chance of getting zapped by "tribo-electrics"
inside this dry box with fans and sundry metal mesh trays. Which are
grounded to earth ground, more or less, through steel pins resting on
aluminum rails... I did not want lightning to strike signal ground, nor
any wire in that harness. My fear of these discharges may be overblown but
I'm chasing gremlins & have no clue what to measure where!
This is my introduction to ground loops then. Although I have difficulty
seeing a "loop" in this scenario.
To thicken the plot, how about connecting shield to ANALOG ground? I'd
hate to have the ADC zapped!

Thank you for your insights.


On Tue, 03 May 2005 02:58:15 -0700, Art <plotsligt@comcast.net> wrote:

Actually you may be inducing a ground loop signal by connecting one end
to a
known 'earth ground'. This will tend to skew the information [create
noise]
at the receiving end. As posted, try connecting one end to equipment
reference [ground] rather than the true 'earth ground'. Seen a lot of
problems in CCTV systems as a result of earthing the cable shields.
"John - KD5YI" <groups5munge@verizon.net> wrote in message
news:AuDde.8666$nN.7137@trnddc05...
Fritz Oppliger wrote:

To protect an analog signal we replaced plain ribbon cable with
shielded
ribbon cable.
The shielding we connected to earth ground on ONE end. Now the
humidity
reading is erratic. Switching back to plain unshielded ribbon and the
problem goes away. This defies all the rules in my book - What could
I
be overlooking?

Earth ground? Try connecting the shield to the circuit ground (common)
at
one end. Then try the other end.

Good luck.

John

--
Fritz Oppliger