Linear Technology 1979A Manual page 3

appenDix
One especially useful purpose for the DC1979A is to
provide precision measurements in higher voltage cir-
cuits. The usual 10MΩ presented by most instruments
will often unacceptably load such circuits and give highly
erroneous results. For providing a wide-range signal
buffer, the GAIN jumper is set to 1× so that the only
errors are from the V
OS
the LTC6090. With a ±50V reading on a 4½ digit DMM
(i.e., 200V scale), this error is generally less than one
count of the display (10mV), even for a several-GΩ source
resistance signal. If one desires to use the DC1979A as
a permanent high voltage buffer unit, then the following
information will be helpful.
Figure 2. Base Hole and PCB Location
and input leakage current of
DEMO MANUAL DC1979A
THE CONSTRUCTION
The following sketches show the hole placement for the
BNC connectors and an optional toggle switch. The toggle
switch is for use with a 9V battery that can fit inside the
case, or other provisions could be made to provide power
connections to the board as desired (for example, a banana
jack, wall-wart DC jack, etc.).
Figure 2 provides the hole placement for the OUT signal
(on J2). This is to pass the output signal through the
bottom of the case using a back-mounted Connex
112404 vertical BNC connector. Two 4-40-1/4" screws
are needed to mount the PCB to the case.
Figure 3 shows the hole placement for the end panel. It
includes the IN signal on J1 using a Molex SD-73100-0105
right-angle BNC connector on the top side of the board,
and the smaller hole is for the miniature toggle switch,
such as from the manufacturer, C&K.
Figure 3. End Panel Hole Locations
dc1979af
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