UG-261 Datasheet, PDF (5/8 Pages) Analog Devices – The EVAL-INAMP-62RZ is designed for evaluation

Evaluation Board User Guide
GUARD DRIVERS
When interference from sources such as power lines must be
reduced to levels below those provided by standard shielded
cables, guard drivers may be effective. A guard equalizes the ac
potential between the in-amp input and the cable shield of the
line, effectively reducing the low frequency interference voltage.
A2 in Figure 3 is a dual op amp AD708 driving the shield(s) of
the input cable(s) from the gain resistor pins of the in-amp. The
voltages at these pins are equal to the input voltages plus 0.6 V
(see the device data sheet).
The EVAL-INAMP-62RZ provides single and differential guards.
Differential guards drive the shields with essentially the same
signals as the inputs, whereas the single guard can be used for
dual conductor cables. In this mode, the +GUARD drives the
shield at ½(VIN DIFF) + 0.6 V.
To activate the guard drivers, +VAUX and −VAUX must be connected.
For shielded cables at both inputs, install the W1, W2, W5,
and W8 jumpers.
Using a Single Guard
When using the AD620, AD622, and AD623 for gains greater
than 1, install Resistors R6 and R11 (which are each half the
calculated resistance of RG) and Jumpers W1, W2, and W10.
For a gain of 1, either Position R6 or Position R11 can be shorted
to enable the guard driver input. Connect the shield to +GUARD.
On the header pins that do not bear the ground symbol, insert a
shunt across Position W1.
The guard drivers can be assembled using the components
listed in Table 6.
UG-261
COMPONENT LOCATIONS
Figure 3 shows the component layout and the location of
connections for the EVAL-INAMP-62RZ board.
POWER
INPUT
OUTPUT
Figure 3. Component Location for the EVAL-INAMP-62
Rev. C | Page 5 of 8