Tektronix ADA400A Instruction Manual page 26

Adjusting the Offset
Controls
Limiting Bandwidth
Maximum
Single-Ended Input
Figure 11: Input and Offset Range for X 100 Gain
Setups that have a large DC offset, but must measure small changes in DC
voltage or signal voltage below 2 Hz, require that you to adjust the offset
controls of the preamplifier. Typical setups include those with transducers or
setups that measure galvanic potentials.
To compensate for a DC offset, perform the following procedure:
1.
ny
Set the input coupling to GND on both inputs of the preamplifier and switch
offset controls to OFF.
Preset the GAIN switch of the preamplifier and the volts/division switch of
the oscilloscope to the appropriate settings based on the amount of offset you
expect to measure. See Figures 8 through 11. (Select a lower gain setting if
you are unsure of the amount of the offset.)
Center the oscilloscope display using the vertical position control on the
oscilloscope.
Set the offset controls ON and center the display with the COARSE and
FINE offset controls.
Set the input coupling to DC on the signal input(s) and, if necessary,
Center the display using the COARSE and FINE controls and change the
volts/division setting on the oscilloscope to better display the signal.
The ADA4OOA Differential Preamplifier has a selector for limiting the upper
bandwidth. Limiting the bandwidth is desirable in setups where electrical
interference from higher frequency sources is a problem. The ADA400A
ADA4OOA Instruction Manual