Specifications

Recommended Wiring and Noise Reduction Techniques
Unshielded signal wiring is very common in Data Acquisition applications. While
this worked well for low speed integrating A/D measurements and/or for measuring
high level signals, it does not work for high speed sampling A/Ds, particularly
when measuring low level signals like thermocouples or strain gage bridge outputs.
Unshielded wiring will pick up environmental noise, causing measurement errors.
Shielded, twisted pair signal wiring, although it is expensive, is required for these
measurements unless an even more expensive amplifier-at-the-signal-source or
individual A/D at the source is used.
Generally, the shield should be connected to ground at the DUT and left open at the
VT1419A. Floating DUTs or transducers are an exception. Connect the shield to
VT1419A GND or GRD terminals for this case, whichever gives the best
performance. This will usually be the GND terminal. A single point shield to
ground connection is required to prevent ground loops. This point should be as
near to the noise source as possible and this is usually at the DUT.
Wiring Checklist The following lists some recommended wiring techniques.
1. Use individually shielded, twisted-pair wiring for each channel.
2. Connect the shield of each wiring pair to the corresponding Guard (G)
terminal on the Terminal Module .
3. The Terminal Module is shipped with the Ground-Guard (GND-GRD)
shorting jumper installed for each channel. These may be left installed or
removed, dependent on the following conditions:
a.
Grounded Transducer with shield connected to ground at the
transducer: Low frequency ground loops (dc and/or 50/60 Hz) can
result if the shield is also grounded at the Terminal Module end. To
prevent this, remove the GND-GRD jumper for that channel.
b.
Floating Transducer with shield connected to the transducer at the
source: In this case, the best performance will most likely be achieved
by leaving the GND-GRD jumper in place.
4. In general, the GND-GRD jumper can be left in place unless it is necessary
to break low frequency (below 1 kHz) ground loops.
Wiring and Noise Reduction Methods
372 Appendix D
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