Measurement Computing CIO-DAC08/16 - Manual (Page 11)

3.7 SIGNAL CONNECTION
The analog outputs of the CIO-DAC16/16 and the DAC08/16 are two-wire hook-ups;
a signal, labeled D/A # OUT on the connector diagram after this section, and a Low
Level Ground (LLGND). The low level ground is an analog ground and is the ground
reference which should be used for all analog hook-ups.
Possible analog output ranges are:
Bipolar Ranges ±10V ±5V
and
Unipolar Ranges 0 to 10V
0 to 5V
Each of the DAC outputs are individually buffered through an OP-27 operational
amplifier (OP-AMP). The OP-27s are socketted so that if one goes bad it can be
replaced in the field. The OP-27 for each channel is located just below the calibration
potentiometers for that channel.
Each channel is capable of sinking or sourcing ±5 mA. That means a load of 2K
Ohms can be connected to each channel at the full rated output swing of +10V.
As the load resistance is raised from 2K up to 10 Meg
Ω
or more, the output load on
the DAC decreases. Any resistance greater than 2K is acceptable.
As the load resistance decreases, the output load increases. The OP-27 responds by
producing a lower output voltage. If your DAC board will not produce the output
voltage specified by the code & range combination, check the load with an ohmmeter.
Under normal circumstances you will not damage the OP-27 by connecting the output
to ground. If your connection results in a failure of the OP-27, chances are good that
there was some potential at the connecting point in addition to a load at ground or
between 0 and 2K ohms. Explore the point with a DVM before reconnecting the
CIO-DAC16/16 or DAC08/16 (and after replacing the OP-27 of course). Connect the
negative lead of the DVM to any LLGND pin of the CIO-DAC16/16 or DAC08/16.
7