Measurement Computing PCM-DAC08 - Manual (Page 14)

Devices to be controlled should be connected with the high side to the numbered ana-
log output and the low side to the analog ground.
Digital signals should not be grounded to the analog ground. Use the digital ground
or the cable shield.
4.2 CONNECTING DEVICES TO THE ANALOG OUTPUTS
The PCM-DAC08 analog outputs are single ended. There is an analog ground for
each analog output channel. When connecting multiple channels you must be sure
that pin 1 is the ground for channel 0, pin 2 and that pin 3 is the ground for channel 1,
pin 4. Also, there should be no measurable potential between the grounds at pins 1, 3
7 and chassis ground.
In addition to avoiding potentials between signal grounds, you must also avoid poten-
tials bewteen signal ground and chassis ground on your computer. If you are using a
laptop and are on battery power, the computer is floating with respect to earth ground,
but the laptop is on the charger unit or on wall power, the laptop may be grounded.
Whenever the computer is grounded, you must connect signals so there is no potential
between PC ground and signal ground. If there is a potential, it will be added to the
signal. For example, if your PCM-DAC08 is supplying 3.5 volts and there is a poten-
tial of -1.5V between the PC and the sensor ground, your device under control will be
reading 2.0V instead of 3.5V
4.3 OUTPUT VOLTAGE RANGES
There is one possible output voltage range of ±5V.
4.4 SIGNAL CONNECTION
The outputs of the PCM-DAC08 are two wire voltage. There is a polarity associated
with the two wires and thus the outputs are labled Analog Out Channel # and Ground,
on the connector.
The maximum current supplied by the analog outputs is 2.5mA. Therefore the mini-
mum resistance, or maximum load which the output may drive is 2K Ohms. Loads
greater than 2K Ohms will cause the analog output to droop, meaning that a code of
4095 will not be able to generate a voltage of 5V, but one somewhat less.
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