Spider DSA User’s Manual
212
Connections between strain gages and the Spider equipment are best made using
26 AWG stranded tinned-copper wire. Choose a jacketed two-wire cable for
Quarter-Bridge installations and three conductors jacketed cable for full and half
bridges. If long cable runs are expected, consider the use of a shielded cable to
reduce induced electrical noise. If extreme accuracy at distance is required, add
two more conductors to your cable and employ Remote Sensing.
The conductors are soldered to the gage solder tabs at the test specimen end. At
the Spider end, the connections are normally made to the screw terminals of an
Input Channel Adaptor (ICA) “breakout” box shown in figure xx2. For a more
permanent installation, you may prefer to solder the leads directly to a dedicated
LEMO connector. It is always good practice to tag or label the cable at the Spider
end, identifying the gage location and specifics of the measurement, the bridge
type, the gage nominal resistance (120or 350 ohm) and the gage factor (GF).
You will make connections to at least two of the seven inputs (IN+, IN-, EXC+,
EXC-, SEN+, SEN- and GND) provided by each Spider-80SG input channel. If a
shielded cable is employed, always connect the shield to GND (and never attach it
to the test structure).
Quarter Bridge Connections
The quarter bridge configuration utilized one strain gage connected to the EXC+
and In- inputs of a Spider-80SG channel. No other connections are required.
Strain gages are not polarized, so it does not matter which side of the gage is
connected to which input. The Spider-80SG provides the other three resistors to
complete the bridge. During software setup, you specify the gage to be either a 120
or 350-ohm unit, and Spider-80SG switches in a matching value resistor to
complete the bridge.
Figure xx7: Quarter Bridge (Type 1) connections
Strictly speaking, this configuration is termed a Type 1 Quarter Bridge. As
previously discussed, the output voltage of this configuration is:
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